an

liaga, N

Hostparasite interface

cocctedc anch sd ttoong

but subsequently has stimulated much international and collaborative research on Echinococcus. 2014 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.

ause ocance2012;rategiete cont

much of the research that revealed the unique features of the par-asites way of life were undertaken in Australia. This is not a coin-cidence and relates to the impact Echinococcus had on a developing

ical Journaeing unde

debate raging at the time on whether cystic and alveolar hydatiddisease were caused by the same or different species of Echinococ-cus (dualists versus monists) as well as his collaboration withresearchers in Europe such as Flix Dv.

Dew recognised the developmental differences of the twostages in the life cycle and studied the metacestode stage ofthe cystic and alveolar forms (Fig. 1) in depth, both in humancases and animals (Dew, 1922, 1925, 1928, 1935). He thus

Tel.: +61 8 9360 2466; fax: +61 8 9310 4144 (R.C.A. Thompson). Tel./fax: +61 026933 4179 (D.J. Jenkins).

E-mail addresses: a.thompson@murdoch.edu.au (R.C.A. Thompson), djjenkins@csu.edu.au (D.J. Jenkins).

International Journal for Parasitology 44 (2014) 865877

Contents lists availab

International Journa

.e land a unique, cystic larval stage in the tissues of non-carnivorousmammals and omnivores (Thompson, 1995). It is interesting that

on hydatid disease in Australia. This was enhanced by Dews con-tributions in the literature (Dew, 1953) and at conferences to theIt is now well known that Echinococcus has a two-host life cyclewith a sexual stage in the intestine of a carnivore denitive host

the British Journal of Surgery and British Medled to widespread recognition of the research bhttp://dx.doi.org/10.1016/j.ijpara.2014.07.0050020-7519/ 2014 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.uch asl thatrtakenHydatid disease, cystic and alveolar, is a typical cyclozoonosisthat can be perpetuated in nature in wild animal cycles with-out impacting on public health but with human interference(Thompson, 2013), directly or accidentally, with spillover todomestic cycles can lead to severe clinical disease and death. It isalso an important cause of economic losses to livestock industries,particularly Echinococcus granulosus in sheep and cattle (Table 1).

incidence of cystic hydatid disease in Australia, and to a lesserextent alveolar hydatid disease, either contracted in Australia(E. granulosus) or in migrants from endemic areas overseas(E. granulosus and Echinococcus multilocularis) (Dew, 1935). Therewas thus a need for regular surgical intervention. It was surgeonssuch as Harold Dew who had an interest in the basic biology ofthe parasite and who published in international journals sTaxonomyEpidemiologyWildlifeDomestic hosts

1. Introduction

Echinococcus remains a major cpublic health and economic signiBudke et al., 2006; Davidson et al.,2013). Despite advances in control stand vaccine development, the parasitries throughout the world.f zoonotic diseases of(Jenkins et al., 2005b;Hegglin and Deplazes,s, clinical managementinues to thrive in coun-

agricultural society following early European settlement of a con-tinent with huge temperate areas perfect to exploit for raisinglivestock.

It was the upsurge in sheep farming at the end of the 19thcentury, with expanding exports to Europe, that contributed tothe serious and largely undocumented human health problem thatexisted during the late 19th and early 20th centuries (Gemmell,1990). During the rst half of the 20th century, there was a highDevelopmentCytodifferentiation

biology, gene regulation, strain variation, wildlife diseases and models of transmission dynamics. Wedescribe the development, nature and diversity of this research, and how it was initiated in AustraliaInvited Review

Echinococcus as a model system: biology

R.C.A. Thompson a,, D.J. Jenkins b,a School of Veterinary and Life Sciences, Murdoch University, Murdoch, WA 6150, AustrabAnimal and Veterinary Sciences, Charles Sturt University, Locked Bag 588, Wagga Wag

a r t i c l e i n f o

Article history:Received 11 June 2014Received in revised form 19 July 2014Accepted 21 July 2014Available online 11 August 2014

Keywords:Echinococcus

a b s t r a c t

The introduction of Echinoareas of the country inican investment in both basiof Echinococcus. This researtal biology and ecology, anfrom fundamental biologyinternational, diverse and

journal homepage: wwwd epidemiology

SW 2678, Australia

us to Australia over 200 years ago and its establishment in sheep rearinga serious medical and economic burden on the country. This resulted ind applied research aimed at learning more about the biology and life cycleerved to illustrate the uniqueness of the parasite in terms of developmen-he value of Echinococcus as a model system in a broad range of research,theoretical control systems. These studies formed the foundation for anoing research effort on the hydatid organisms encompassing stem cell

le at ScienceDirect

l for Parasitology

sevier .com/locate / i jpara

Known denitive hosts Infectivity tohumans

ts, macropods) Dog, fox, dingo, jackal and hyena YesDog, fox YesDog YesDog Probably notDog YesWolves, dog YesDog Yes

beest,ope, giraffe,

Lion Uncertain

g, dog, monkey Fox, dog, cat, wolf, racoon-dog,coyote

Yes

Tibetan fox UncertainBush dog YesWild felids Yes

2005b), Thompson (2008), and Carmena and Cardona (2014).

host tissue

adventitial layer

laminated layer

germinal layer

a

b

c

d

d

e

vesicles

E. granulosus

A

B

l Joucomplemented much of Dvs research undertaken in rodents(Dv, 1919, 1946) and built on this. Dew demonstrated that anintact laminated layer was a fundamental and unique componentof the healthy hydatid cyst and considered this layer to be of hostorigin, and demonstrated that elements of the cyst wall (germinallayer) could regenerate (Dew, 1935). He realised that the cystenclosed a sterile environment and was under intracystic pressure,and speculated on the reasons for this being indicative of viabilityand a function of the germinal layer. In observations of what wenow know to be the metacestode of E. multilocularis, Dewdescribed naked prolongations of the nucleated germinal mem-brane (layer) in direct contact with host tissues (Dew, 1935), a fun-damental feature of the inltrating metastatic metacestode of E.multilocularis (Fig. 1) subsequently described using electronmicroscopy 60 years later (Mehlhorn et al., 1983; and see Sec-tion 2.4). Thus it was Harold Dew that led to Australia beingreferred to as the home of hydatids in terms of research. He pavedthe way for other researchers and did much to establish Echinococ-cus as a model organism. In this country of Australia we all haveunrivalled opportunities to investigate this disease, both in manand in animals, and it is our duty to contribute our share to futureadvances in its study (Dew, 1935).

The economic impact and public health signicance of cystic

Table 1Current taxonomy of Echinococcus spp.

Species Strain/genotype Known intermediate hosts

Echinococcus granulosus Sheep/G1 Sheep (cattle, pigs, camels, goaTasmanian sheep/G2 SheepBuffalo/G3 Buffalo

Echinococcus equinus Horse/G4 Horses and other equinesEchinococcus ortleppi Cattle/G5 CattleEchinococcus canadensis Cervids/G8,G10 CervidsEchinococcus intermedius Camel/Pig/G6/G7 Camels, pigs, sheepEchinococcus felidis Lion/ Warthog (possibly zebra, wilde

bushpig, buffalo, various antelhippopotamus)

Echinococcusmultilocularis

Some isolatevariation

Rodents, domestic and wild pi

Echinococcus shiquicus / PikaEchinococcus vogeli None reported RodentsEchinococcus oligarthrus None reported Rodents

Data from: Thompson et al. (1995), Thompson and McManus (2002), Jenkins et al. (

866 R.C.A. Thompson, D.J. Jenkins / Internationahydatid disease in Australia worsened over the next 30 years,which provided an opportunity for obtaining research fundsfrom organisations supporting health and livestock research. J.D.Smyth obtained funds from these sources and took a physiologicalapproach in his research aimed at increasing understanding of thedevelopmental biology of Echinococcus. Having forged an interestin developing in vitro cultivation procedures for Schistocephaluswith success in establishing much of the life cycle of this cestodein culture (Smyth, 1946, 1950), he turned his attention to Echino-coccus (see Smyth, 1990) for which the ability to study and main-tain the parasite in vitro would provide a great research tool forinvestigating methods of control.

The practical and ethical difculties of undertaking in vivostudies in the canid or felid denitive hosts of Echinococcus furtherreinforced the need to develop in vitro systems. It was these pio-neering studies of Smyth (Smyth et al., 1966 and reviewed inSmyth and Davies, 1974a; Howell and Smyth, 1995) that demon-strated the potential of Echinococcus as a model for studyingprinciples of developmental biology, differentiation, hostparasiterelationships and evolutionary biology (Smyth, 1969; Smyth et al.,1966), and which have inuenced research and theoretical under-standing far beyond parasitology (Thompson and Lymbery, 2013).Smyth saw the potential of exploiting Echinococcus as a novelrnal for Parasitology 44 (2014) 865877model system for studying parasitism as distinct from a modelfor studies on evaluating anthelmintic or other anti-parasitic drugs(Smyth, 1969). He thus expanded the denition of a model toembrace studies on all the biological activities that supported the

distantmetastaticfoci

circulation

protrusions of germinal layer

E. multilocularis

Fig. 1. Diagrams illustrating the structural differences between the metacestodes of(A) Echinococcus granulosus (ad, stages in development of protoscoleces and broodcapsule; e, daughter cyst) and (B) Echinococcus multilocularis (redrawn fromThompson, 1995).

in the gut of the denitive host that strobilate development wasobtained (Smyth et al., 1966). Smyth took a physiological approach

l Jouto this research, with the cyst as a starting point. Its sterile environ-ment provided the perfect entry point if accessed aseptically tocarefully remove essentially dormant invaginated protoscolecesand then expose them to appropriate physiochemical conditions(Smyth and Davies, 1974a). Of particular signicance was theprovision, in addition to the liquid medium, of a solid proteina-ceous base in the culture ask (diphasic medium) which was foundto be important in stimulating proglottisation and segmentation inE. granulosus with maturation to the pre-fertilisation stage(reviewed in Smyth and Davies, 1974a; Howell and Smyth,1995). Similar results were obtained with E. multilocularis butproglottisation without segmentation will take place without asolid proteinaceous base (Smyth and Davies, 1975; Smyth, 1979;Thompson et al., 1990). This and other developmental abnormali-ties observed in E. multiloculariswere considered to reect a differ-ence in gene expression between the two species (Howell andSmyth, 1995 and see Section 2.3). Although the conditions devel-oped supported reproducible strobilate development, fertilisationparasite life style of Echinococcus, as well as the potential of thismodel system for broader studies of a more fundamental naturein biology, for example stem cells (Smyth, 1969, 1987). As suchthe promotion of such a eukaryotic, metazoan model was at thetime somewhat of a rst.

Smyth worked closely with his Australasian colleague MichaelGemmell, who also had an interest in Echinococcus but who waskeen to understand the epidemiology of hydatid disease, its eco-nomic impacts and impediments to control (Gemmell, 1990). Assuch, he was the rst to apply mathematical models to Echinococ-cus and the concept of the basic reproductive rate (R0) in order todene the conditions under which transmission of Echinococcusand other taeniids occur, and the regulatory role of immunity(Gemmell, 1990; Gemmell and Roberts, 1995).

In this review, we describe the research, particularly thatundertaken in Australia, which has demonstrated the value of Echi-nococcus as a model system inuencing advances in biology andepidemiology of parasites and parasitic infections.

2. Developmental biology

2.1. Growth and maturation

Echinococcus has two developmental stages in its life cycle; theadult tapeworm, which is the sexual stage, and the cystic or inl-trative larval metacestode that reproduces asexually (Fig. 1). Themetacestode of E. granulosus, which was easily accessible frominfected livestock in the abattoir or from human surgical cases,was the logical starting point for experimental manipulations. Ini-tially, these were undertaken in rodents where the asexual prolif-erative nature of the parasite was rst observed, a phenomenonthat was subsequently exploited with the development of rodentmodels of secondary hydatidosis (Dv, 1919). These provided ameans to maintain the parasite virtually indenitely in vivo byserial passage (e.g., Thompson, 1976; Whiteld and Evans, 1983;Kamiya et al., 1985).

Although a number of workers had reported vesicular/cysticdevelopment and proliferation of protoscoleces in vitro, a majorgoal was to provide appropriate conditions to stimulate and sup-port development in an adult (strobilate) direction. It was not untilSmyth and his colleagues rened procedures with the aim toreproduce the conditions that protoscoleces would be exposed to

R.C.A. Thompson, D.J. Jenkins / Internationaand egg production eluded Smyth and other workers. However,they served to emphasise the complexity of the process and tosupport observations made from in vivo and population geneticstudies of the importance of the host intestinal ecosystem inproviding the correct physical and physiochemical conditionsnecessary to support fertilisation (Smyth, 1982; Smyth andDavies, 1974a; Lymbery and Thompson, 1988, 2012; Lymberyet al., 1989; Howell and Smyth, 1995).

The success with cultivating Echinococcus and the elucidation ofconditions that would support maturation stimulated studies onother taeniids including Taenia pisiformis and Taenia crassiceps(Esch and Smyth, 1976; Osuna-Carrillo and Mascar-Lazcano,1982), as well as Mesocestoides corti (Barrett et al., 1982;Thompson et al., 1982). These largely supported the observationsmade with Echinococcus but also served to illustrate the unique-ness of the Echinococcus model system.

During the 25 years Smyth and his colleagues spent studyingand optimising strobilate development and maturation of Echino-coccus in vitro, many valuable observations were made that haveserved to establish Echinococcus as a model system not only interms of developmental biology, but also for cytodifferentiationand the hostparasite interface.

2.2. Developmental plasticity

Studies on the in vitro cultivation of Echinococcus from thelarval protoscolex to the adult worm demonstrated the inherentplasticity of the parasite a phenomenon eloquently describedas heterogeneous morphogenesis (Smyth et al., 1967; Smyth,1987), unique in most metazoan organisms apart from coelenter-ates such as Hydra, and making Echinococcus an unusual modelfor differentiation studies. Depending upon the culture conditions,protoscoleces can either develop in a cystic or adult direction. Cys-tic development itself may take a variety of paths, again inuencedby environmental conditions. These alternative developmentalpathways have been described in detail by Howell and Smyth(1995). Protoscoleces can also develop into an adult tapewormunder different conditions to those supporting cystic development,most importantly the need for a diphasic medium incorporating asolid supporting substrate thought to provide nutrients and/or acontact stimulus (see Section 2.1). However, observations on thedevelopment of adult E. granulosus and E. multilocularis demon-strated that in addition to normal worms, cultures often con-tained worms that had matured but not segmented (monozoic)and worms with more than one scolex and other malformations(reviewed in Howell and Smyth, 1995). Interestingly, adult wormsthat have developed from protoscoleces can de-differentiate in acystic direction under adverse conditions (see Sections 2.3 and2.4; Smyth, 1969; Thompson and Lymbery, 1990; Thompsonet al., 1990). These observations raised two important and funda-mental questions: how is this complex and plastic developmentcontrolled and what cells have the potential to develop in such amyriad of different routes?

2.3. Developmental control

Smyth developed a hypothetical yet logical model to explainhow genes regulate differentiation and developmental shifts inEchinococcus (Smyth, 1969). This was based on the JacobMonodmodel of genetic expression and showed the complex interactionsand regulatory switches that may be involved in controlling devel-opment and differentiation in Echinococcus. Since then a number ofstudies have isolated and characterised regulatory genes from Echi-nococcus (reviewed in Thompson, 1995 and Parkinson et al., 2012)but how they t together in a control network has yet to be deter-mined. Recently, Parkinson et al. (2012) identied long non-coding

rnal for Parasitology 44 (2014) 865877 867(nc)RNAs that may be involved in the regulation of gene expressionin response to environmental cues in the host. They also identieda number of genes reecting specicities of particular stages,

coccus germinal cells has now been achieved for both species(Yamashita et al., 1997; Spiliotis and Brehm, 2009; Spiliotis et al.,

l Jou2008; Albani et al., 2010). The germinal cells behave similarly toclassical stem cells with the formation of cell aggregates and clus-ters with cavity formation, and there is cytological evidence oftransformation (Spiliotis et al., 2008; Albani et al., 2013).

Galindo et al. (2003) found evidence of the regionalisation ofDNA and protein synthesis in developing stages of Echinococcus,although no morphological evidence has been found of differentprimitive or germinal cell lines to explain the concept of heteroge-including those whose expression is up-regulated by pepsin-acidactivation. It is to be hoped that Smyths models will help to pro-vide functionality to the genomic data that is now available forboth E. granulosus and E. multilocularis (Tsai et al., 2013; Zhenget al., 2013). However, differences in development between E.granulosus and E. multilocularis highlighted by studies in vitro areconsidered to reect differences in the control of gene expression(Howell and Smyth, 1995).

2.4. Cytodifferentiation

Slais (1973) demonstrated that the post-oncospheral develop-ment of Echinococcus was initiated by the growth and division ofprimary germinal cells, and Swiderski (1983) described ve pairsof these cells in the posterior pole of the oncosphere. Observationson the development of Echinococcus in vitro demonstrated that thefundamental processes of germinal and somatic differentiation,comprising cystic development, proglottisation, maturation,growth and segmentation (strobilisation), can take place indepen-dently. This not only illustrated the complexity of cytodifferentia-tion but also the possible existence of several primitive cell lines.However, to date all the evidence suggests that only one primitivemorphological cell type exists as a pool of uncommitted, undiffer-entiated multipotent germinal, or stem, cells in both the adult andmetacestode (Smyth, 1969; Gustafsson, 1976; Thompson et al.,1990; Thompson, 1995; Koziol et al., 2014). The undifferentiatedgerminal cells are a component of the syncytial germinal layer ofthe metacestode and neck region of the adult cestode. Ultrastruc-tural studies reveal unremarkable rounded cells of variable sizeof approximately 4 lm diameter (Gustafsson, 1976; Mehlhornet al., 1983; Albani et al., 2010). Cell proliferation derives fromthe continuous replicative activity of these dividing stem cellslocated in the germinal layer or neck region of the adult tapeworm(Gustafsson, 1976; Galindo et al., 2003). They have considerableproliferative potential (Eckert et al., 1983; Mehlhorn et al., 1983;Galindo et al., 2003; Martnez et al., 2005), and are the only prolif-erating cells in Echinococcus (Koziol et al., 2014). This is particularlywell illustrated by the capacity of the parasite for indenite perpet-uation in the larval stage by passage of protoscoleces or germinallayer material in rodents (secondary hydatidosis; Howell andSmyth, 1995). In alveolar hydatid disease caused by the metaces-tode of E. multilocularis, the proliferating larval parasite has aninltrative capacity to establish distant foci of infection due tothe distribution via blood or lymph of detached germinal cells(Ali-Khan et al., 1983; Eckert et al., 1983; Mehlhorn et al., 1983;Fig. 1).

Problems with host cell contamination dogged early attemptsto establish germinal cell lines of E. granulosus and E. multilocularis(reviewed in Howell and Smyth, 1995). In addition, their isolationfrom the germinal layer, and their in vitro propagation, could havebeen hampered by the fact that the germinal layer is a syncytium.However, the establishment and long-term perpetuation of Echino-

868 R.C.A. Thompson, D.J. Jenkins / Internationaneous morphogenesis (Smyth, 1969). However, such heterogeneityhas now been conrmed at the molecular level. Germinal cells arein fact heterogeneous, with the existence of subpopulations withdifferent gene expression patterns (Koziol et al., 2014), thus con-rming Smyths predictions.

2.5. Hostparasite interface

2.5.1. Denitive hostObservations that contact of the scolex with a proteinaceous

base stimulated strobilate development in E. granulosus led tostudies on the nature of the interface both in vitro and in vivo,and the discovery of the rostellar gland which comprises a modi-ed group of tegumental cells situated in the apical rostellum(Smyth, 1964; Smyth et al., 1969; Thompson et al., 1979;Thompson and Eckert, 1983; Fig. 2). The rostellar gland releasessecretory material by a holocrine process into the interfacebetween parasite and host (Thompson et al., 1979). The originand site of synthesis of the secretion has still to be determined,although large amounts occur in both the perinuclear and distalcytoplasm of the tegument as well as in the tegumental nuclei(Thompson et al., 1979; Herbaut et al., 1988). The secretion is pro-teinaceous, containing cystine and lipid. It is not known if there areone or more proteins secreted but Siles-Lucas et al. (2000) demon-strated that the secretion contains a regulatory protein (14-3-3)that is released into the hostparasite interface.

The rostellar gland of Echinococcus is seemingly unique toEchinococcus. Although rostellar secretions have been describedin larval T. crassiceps (Krasnoshchekov and Pluzhnnikov, 1981),no gland has been described. Rostellar glands have been describedin other adult cestodes, particularly proteocephalids, but theirfunction is also unclear and structurally they are different to therostellar gland in Echinococcus (McCullough and Fairweather,1989; Zdrsk and Nebesrov, 2003). There is clearly a need formore studies on the interface of attached adult cyclophyllideancestodes (Pospekhova and Bondarenko, 2014).

This intimate association of the rostellar gland and itssecretions suggests a role(s) that enhances the hostparasiterelationship in favour of the parasite, which may be regulatory,nutritional and/or protective. The relationship between rostellargland activity and localised humoral and cellular reactions(Deplazes et al., 1993) is not known but such localised reactionsdemonstrate stimulation of host immune effector mechanisms.The secretory molecules would seem to be obvious candidatesfor exploitation in vaccine studies since a focus on prophylaxis ofthe denitive host may be more attractive than the intermediatehost, particularly for the control of E. multilocularis, from both com-mercial and practical perspectives. As pointed out by Heath (1995)the scolex is in intimate contact with the systemic circulation evenin the Peyers patches and would appear to maintain its privilegedintegrity by suppression of cytotoxic and effector cell activity inthe region of the scolex.

The few studies on denitive host vaccines do not seem to havetargeted rostellar gland secretions and have produced resultswhich are controversial and open to contrasting interpretation(Zhang et al., 2006; Petavy et al., 2008; Torgerson, 2009;Kouguchi et al., 2013). The studies by Petavy et al. (2008) demon-strated a strong inammatory response in the intestine of vacci-nated compared with infected controls but did not show if thiswas localised to where worms were situated. More recently,Kouguchi et al. (2013) used a surface glycoprotein from E. multiloc-ularis as a vaccine in dogs which induced signicant protectionwhen administered via a mucosal route and demonstrated anti-bodies raised by their vaccine on the surface of the suckers, rostellaand hooks. These results emphasise the importance of characteris-ing the secretions produced by the rostellar gland of Echinococcus

rnal for Parasitology 44 (2014) 865877which will contribute to the further development of vaccinesagainst the adult parasite. Unfortunately in vivo studies requireresearch on the denitive host, usually dogs, which is ethically

immune-regulatory role of the laminated layer, probably in associ-

n thown

l Jouchallenging and hazardous if patent infections are maintained.Thus reports of successful patent infections in experimentallyinfected immunosuppressed rodents (Kamiya and Sato, 1990a,b)were regarded as an important breakthrough (Howell and Smyth,1995; Thompson, 1995). Unfortunately, these results have notbeen further exploited and should perhaps form the basis forA

Fig. 2. Diagram illustrating adult Echinococcus in situ in the intestine, with suckers ointo a crypt of Lieberkhn (A, B) and extensibility of the apical rostellar region is sh

R.C.A. Thompson, D.J. Jenkins / Internationafuture research.

2.5.2. Intermediate hostA unique interface is also found in the intermediate host where

the laminated layer presents a physiochemical barrier with appar-ent multifunctionality and a structure whose biosynthesis hasbecome a model system for carbohydrate chemistry (Diaz et al.,2011a,b; Parkinson et al., 2012). The laminated layer is a specia-lised extracellular matrix unique to Echinococcus (Fig. 1), whosesynthesis is a major metabolic activity of the much thinner germi-nal layer (Diaz et al., 2011a; Lin et al., 2012; Parkinson et al., 2012).The origin of the laminated layer was controversial for some time,i.e. whether it is entirely of parasite origin or if there is a host con-tribution. Holcman and Heath (1997) demonstrated that it isentirely of parasite (germinal layer) origin by studying the earlystages of cyst development from oncospheres in vitro.

Considerable metabolic activity in the germinal layer isrequired to synthesise and maintain the interfacial barrier of thelaminated layer (Parkinson et al., 2012). The role of the laminatedlayer would appear to be one of protection since cyst survival isdependent upon its integrity (Gottstein et al., 2002). Whether thisis purely physical or if there is selective permeability is not known.Monteiro et al. (2010) identied several molecules in hydatid cystuid that could play a role in host evasion. Smyth commented onthe signicance of the presence of a human blood group P-like sub-stance in the laminated layer of Echinococcus and its signicance asa model system in better understanding the immunological basisof the host-parasite relationship. This P1 blood-antigen motif hassince attracted much attention and has been further characterisedas a protein-carbohydrate, trisaccharide/mucin complex contain-ing galactosamine, yet no biological function has been describedation with the immuno-modulatory activities of the glycoproteinsknown as Antigen 5 and Antigen B (Diaz et al., 2011b).

2.6. Taxonomy and speciationto date (Lin et al., 2012). There is also increasing evidence of the

B

e scolex grasping the epithelium at the base of the villi. Rostellum is deeply insertedin B. Rostellar gland with secretory material is anterior to the rostellar pad (r).

rnal for Parasitology 44 (2014) 865877 869One of the most important observations made as a result ofstudies on the in vitro cultivation of Echinococcus was the failureof protoscoleces collected from hydatid cysts in horses to developin the same way as those of sheep origin. Protoscoleces from horsesevaginated and increased in length but failed to undergo proglotti-sation or segmentation, even though they were grown in exactlythe same diphasic medium (Smyth and Davies, 1974b). This fairlysimple observation resulted in radical shifts in our understandingof the epidemiology of hydatid disease and transmission of theaetiological agents as well as their taxonomy and phylogeneticrelationships. The results demonstrated that there were funda-mental physiological differences between E. granulosus of sheepand horse origin and the coining of the term physiological straindifferences (Smyth and Davies, 1974b; Smyth, 1982). This had abroad inuence beyond Echinococcus, and in particular the impor-tance of combining phenotypic and genetic differences in the char-acterisation and description of parasites at the intraspecic level(Thompson and Lymbery, 1990, 1996; Lymbery and Thompson,2012).

In terms of Echinococcus, the observation of physiologicaldifferences between the two parasites of sheep and horse origincomplemented earlier epidemiological and taxonomic studies onEchinococcus of horse origin (Williams and Sweatman, 1963). Thesedemonstrated morphological differences between the two formswhich were considered to be taxonomically signicant, and toreect differences in host specicity and the life cycles whichmaintained the two parasites. This was subsequently shown tobe correct with the sympatric occurrence of distinct sheep- andhorse-dog cycles in several European countries (Thompson andSmyth, 1975; Thompson, 2001; Gonzalez et al., 2002). In addition,

Much of the basic knowledge regarding the epidemiology and

l Joucontrol of E. granulosus in Australia was generated by MichaelGemmell. His contribution to the eld has been immense; thebreadth of his studies were wide, covering the impact of climateon egg longevity, immune responses against the parasite in den-itive and intermediate hosts, prevalence in domestic dogs and live-stock, studies on infection in wildlife and mathematical modellingof transmission as an aid to more effective control (Gemmell andLawson, 1986). Gemmells work has provided a solid platform formany of the current studies reviewed below. However, probablyhis greatest legacy was his contribution to the development ofstrategies for the control of E. granulosus transmission. Neverthe-less, in the Australian situation, although control of E. granulosus,domestically, has largely been achieved (Jenkins et al., 2014), thepresence of an extensive wildlife reservoir on mainland Australiaensures the compete eradication of E. granulosus is unlikely to everbecome a reality. Further, unlike the situation with E. multilocularisand Echinococcus canadensis which are maintained in natural wild-life cycles, the wildlife cycle in Australia is an articial one estab-lished as a result of anthropogenic activities and spillover fromdomestic cycles (Thompson, 2013).

The work of Gemmell had broad ramications internationally interms of the epidemiological principles of hydatid control. Manysubsequent hydatid control programmes world-wide looked atGemmells critical analysis of the epidemiology in Australia andNew Zealand and based their programmes on his data. Theseserved as a foundation for the development of control programmesin many countries, and the epidemiological principles he devel-oped similarly have been used as a model (Eckert et al., 2001).epidemiological evidence has not only demonstrated distinct dif-ferences in intermediate host specicity but also that, unlike thesheep strain (E. granulosus), the horse strain (Echinococcus equinus)(Table 1) does not appear to be infective to humans (Thompsonand Lymbery, 1988, 1991).

The concept of host-adapted strains of E. granulosus led to stud-ies on other forms of the parasite in other species of intermediatehosts such as cattle, pigs, camels and cervids. These studies notonly conrmed the existence of a number of host-adapted lifecycles in different parts of the world but also provided additionaldata on developmental differences between strains which mayimpact on control (reviewed in Thompson and Lymbery, 1988;Thompson et al., 1995; Thompson, 2008).

Subsequent molecular characterisation of host-adapted strainsof Echinococcus, coupled with molecular epidemiological studies inendemic areas, has conrmed their genetic and morphological dis-tinctness and revealed phylogenetic relationships which support arobust, meaningful taxonomy based on a previously suggestednomenclature (Table 1; Bowles et al., 1994; Thompson et al., 1995,2006; Cruz-Reyes et al., 2007; Harandi et al., 2002; Thompson andMcManus, 2002; Lavikainen et al., 2003; Jenkins et al., 2005a;Romig et al., 2006; Moks et al., 2008; Thompson, 2008; Huttneret al., 2009; Saarma et al., 2009; Nakao et al., 2013). Interestingly,the nomenclature used for these species conforms to that proposedby observational parasitologists in the 1920s1960s, before molec-ular tools were available to conrm their morphological descrip-tions and epidemiological observations (Thompson et al., 1995;Thompson and McManus, 2002; Thompson, 2008).

3. Epidemiology of E. granulosus in Australia

3.1. Introduction

870 R.C.A. Thompson, D.J. Jenkins / InternationaEchinococcus granulosus is the only member of the genus tooccur in Australia, having been introduced with domestic dogsand livestock, mainly sheep, during European settlement(Gemmell, 1990). Domestically, the parasite spread rapidlythrough sheep and dog populations (Gemmell, 1990), due mainlyto a complete lack of understanding of the association betweentaeniid tapeworms in dogs and cysts in sheep. It was not until1851, (63 years after the rst European settlers and their animalsarrived in Australia) that infection experiments were undertaken,demonstrating the relationship between cysts and tapeworms.Kchenmeister, working in Germany, fed metacestodes of T. pisi-formis to foxes and obtained tapeworms (Kchenmeister, 1851)and in 1853 fed tapeworm eggs to sheep and obtained metaces-todes. In the next few years von Siebold and Kchenmeister, work-ing independently, fed protoscoleces of Echinococcus to dogs andobtained tapeworms (von Siebold, 1853; Kchenmeister, 1855).An additional important infection experiment, also undertaken inGermany, was that of Naunyn in 1863 who fed protoscoleces froma human cyst to dogs and obtained adult E. granulosus, reportinghis results the same year. This experiment demonstrated for therst time the association between hydatid cysts of sheep andhumans and the role of dogs in the life cycle of human hydatidosis.However it was not until 1876 that Leuckart demonstrated eggs ofEchinococcus when fed to intermediate hosts (pigs) led to thedevelopment of hydatid cysts (Leuckart, 1876). A detailed reviewof the elucidation of the Taenia and Echinococcus life cycles canbe found in Grove (1990). Word of these discoveries took time toreach Australia but it was not long before experimental studieswere undertaken in Australia that conrmed Naunyns data(Thomas, 1884).

Hydatid disease soon became a major public health problem inthe growing population of new Australians (Gemmell, 1990) caus-ing serious illness and leading to the deaths of many colonists.

3.2. Wildlife hosts of E. granulosus in Australia

Data generated in studies on wildlife in Australia have world-wide relevance, an example being the work of Barnes (Barneset al., 2007a,b, 2008, 2011) investigating the health impacts andgrowth rate of hydatid cysts in macropodids. Barnes showed thathydatid cysts have a major impact on respiration capacity in mac-ropods, indicating infected animals to be more susceptible to pre-dation by wild dogs. This work complements and validates thestudies of Mech (1966) and Jolly and Messier (2004) in the USAwith respect to the impact of hydatid disease on moose (Alcesalces), rendering infected animals more susceptible to predationby wolves (Canis lupus). Another good example is the study onthe encroachment of E. granulosus-infected foxes (Vulpes vulpes)and wild dogs into urban areas in Australia and associated publichealth implications (Jenkins and Craig, 1992; Jenkins et al.,2008). These studies complement and support work undertakenin Europe with the encroachment into urban centres of foxesinfected with E. multilocularis (Deplazes et al., 2004) and studiesin Alberta, Canada on E. multilocularis in urban coyotes (Canislatrans) (Catalano et al., 2012).

Australian native wildlife species evolved in isolation fromE. granulosus; consequently, they were highly susceptible to infec-tion with this new parasite and wildlife species were soon acting asa major sylvatic reservoir for the perpetuation of E. granulosus inAustralia (Durie and Riek, 1952), a situation that prevails today(Jenkins and Morris, 2003).

Initially, transmission of E. granulosus to macropodids occurredthrough accidental consumption of eggs spread in the environmentby the dogs of colonists. Infection in dingoes eventuated throughpredation of sheep on the recently established sheep farms. How-ever, it would not have been long before the dingoes themselves

rnal for Parasitology 44 (2014) 865877began to spread eggs throughout their territories, exposing an everincreasing population of macropodids to infection with hydatiddisease. Transmission of E. granulosus to wildlife from domestic

Infection with adult E. granulosus has never been reported from

Macropodid marsupials are highly susceptible to infection with

l Jouanimals in the more remote areas of Australia was likely to havebeen enhanced through transhumance grazing (King, 1959). Trans-humance grazing was undertaken for over 100 years in the statesof New South Wales and Victoria, with the last Snow Lease inNew South Wales being revoked in 1972. In this process hundredsof thousands of sheep (and tens of thousands of cattle), accompa-nied by drovers and their dogs, were moved to the higher altitudesof the Great Dividing Range each summer to graze the alpine pas-tures. This was a highly organised process where families leaseddened areas of pasture for their animals to graze for 3 - 4 monthseach year. Therefore, annually these pastures would have becomecontaminated with eggs from infected sheep dogs acting as asource of infection of both sheep and macropodids. Dingoes wouldhave been infected through predating on sheep and opportunistscavenging of dead sheep and offal discarded by the drovers whenthey killed a sheep to eat whilst staying on the lease.

3.2.1. DingoesThe Australian wildlife top-order predator coincidentally was a

placental canid, the dingo (Canis lupus dingo), introduced fromsouth-eastern Asia by visiting seafarers (Corbett, 1995). Dingoeswere medium sized wild dogs (1117 kg) capable of killing sheep.

Settlers moving to Australia also brought their domestic dogsand it soon became evident that dingoes were able to breed withdomestic dogs and produce fertile hybrid offspring. The resulthas been that currently in most areas of remaining suitable habitatin south-eastern and eastern Australia the resident top order pred-ator populations no longer consist of pure-bred dingoes but mainlydingo/domestic dog hybrids with occasional pure-bred dingoes(Claridge et al., in press). Animals in these populations are referredto as wild dogs. Pure-bred dingoes are mostly restricted to remoteareas, especially in northern parts of Western Australia. Neverthe-less, there is no indication that hybrid dingoes are any more or lesssusceptible to infection with E. granulosus than pure-bred animalssince no difference in the range of worm burdens has been notedbetween hybrid and pure-bred dingoes (Jenkins and Morris,2003; Jenkins et al., 2008). The hunting and pack behaviours ofdingo hybrids compared with dingoes also appear to be similar(Claridge et al., in press). The one important physiological differ-ence between dogs and dingoes is breeding capacity; femaledomestic dogs come into oestrus twice each year whilst for din-goes it is only once. Data collected on the breeding behaviour ofdingo hybrids does not indicate they are having more litters peryear than pure-bred dingoes, but there have been reports that littersizes in hybrids are larger than those of pure-bred dingoes and thesize of wild dogs has increased approximately 20% during the last40 years (Claridge et al., in press).

Anecdotally, in many areas wild dog population numbersappear to be increasing, a likely combination of increased litter sizeand increased food resources due to environment modication.Provision of more pasture and watering points for livestock hasled to major increases in macropodid populations in many areas,providing increased food supply for wild dogs. With increased wilddog populations it is reasonable to assume that the biomass andrate of transmission of E. granulosus in wildlife is also increasing.

3.3. Echinococcus granulosus-infected wild dog encroachment intourban areas

With increasing wild dog numbers and the spread of urbanisa-tion into areas of hitherto wild dog habitat has displaced youngand old animals seeking new uncontested habitat. These animalsare encroaching into outer urban areas and bringing E. granulosus

R.C.A. Thompson, D.J. Jenkins / Internationawith them (Brown and Copeman, 2003; Jenkins et al., 2008).Reports of E. granulosus-infected wild dog encroachment into

outer suburban areas have begun to appear; Townsville (Brownthe intermediate stage of E. granulosus (Jenkins and Morris, 2003;Banks, 2006), often carrying multiple large metacestodes (hydatidcysts). This is especially the case in a number of wallaby species,namely swamp wallabies (Wallabia bicolor) in south-eastern Aus-tralia (Jenkins and Morris, 2003). Swamp wallabies are commonlyinfected with E. granulosus (Jenkins and Morris, 2003) and are alsoa favourite dietary item for wild dogs (Claridge et al., in press),making them pivotal in the transmission of E. granulosus in wildlifein south-eastern Australia. Other wallaby species appear to be ofsimilar importance in other parts of Australia (Banks et al., 2006a).

Curiously, on the island state of Tasmania macropodid marsupi-als never become infected with E. granulosus (Howkins, 1966),despite there having been high levels of transmission in domesticanimals. This may have been associated with the absence ofdingoes and the presence of a dasyurid top order predator, thethylacine (Thylacine cynocephalus), refractory to infection withE. granulosus (see Section 3.4). Nevertheless, human hydatidosisbecame such a major public health problem in Tasmania that aprogram of intense control was introduced that continued for30 years (Beard et al., 2001).

Other species of native wildlife susceptible to infection with E.granulosus are wombats (Wombatus ursinus). However, hydatidAustralian native marsupial carnivores. In 2005, Jenkins et al.undertook a small study investigating the faeces from wild-caughtspotted-tailed quolls (Dasyurus maculatus) for coproantigens of E.granulosus and reviewed the literature regarding experimentalinfection of dasyurids with E. granulosus. None of the quoll faecestested were found to be positive for coproantigens of E. granulosus(Jenkins et al., 2005a) and in none of the attempted experimentalinfections of several species of dasyurid have E. granulosus beenrecovered. From these data, Jenkins et al. (2005a) concluded thatdasyurids are refractory to infection with E. granulosus.

3.5. Wildlife intermediate hostsand Copeman, 2003), Maroochy Shire (Jenkins et al., 2008), thenorth-western suburbs of Brisbane in the Pine River Shire, Queens-land and the outer suburbs of Katoomba in New South Wales (D.J.Jenkins, unpublished data). In a number of urban areas, wild dogshave become numerous and a public nuisance raiding garbagebins, killing domestic pets and menacing residents. They havebecome such a problem in a number of places that local authoritieshave employed professional wild dog controllers to remove themusing lethal methods. Examination of the intestines of some ofthese euthanised wild dogs from several locations has revealedhigh prevalences and heavy worm burdens of E. granulosus(Brown and Copeman, 2003; Jenkins et al., 2008). The establish-ment of peri-urban transmission cycles are unlikely, but regularencroachment of E. granulosus-infected wildlife denitive hostsinto outer suburbs of urban centres has been demonstrated(Brown and Copeman, 2003; Jenkins et al., 2008), which is difcultto control and likely to be an ongoing issue for local councils tomanage.

Hitherto, it was supposed urban human populations in Australiawere insulated from exposure to E. granulosus, and clearly, with theencroachment of E. granulosus-infected wild dogs (and foxes, seeSection 3.7.1) into urban areas this is no longer the case.

3.4. Australian native carnivores as denitive hosts for E. granulosus

rnal for Parasitology 44 (2014) 865877 871infection in wombats has only been reported once (Grainger andJenkins, 1996). Wombats are consumed periodically by wild dogsbut appear to only be an occasional host for E. granulosus, therefore

l Jouthey cannot be regarded as an important component of the E. gran-ulosus life cycle in Australia.

3.6. Factors contributing to the transmission success of E. granulosus inAustralian wildlife

Hydatid disease of macropodids is almost exclusively connedto the lungs, causing major respiratory impairment (Jenkins andMorris, 2003; Barnes et al., 2007a,b, 2008, 2011) that may lead tothe death of the host (Johnson et al., 1998; Barnes et al., 2008).Why hydatid infection in macropods should be mainly connedto the lungs is unclear, however, this is also seen with hydatidinfection in cervids (Schantz et al., 1995). Hydatid-infected macro-podids are rendered highly susceptible to predation by dingoes, asimilar situation to that with the interaction of wolves and hyda-tid-infected moose (A. alces) in the USA (Mech, 1966; Jolly andMessier, 2004). In addition, cysts in macropodids develop quickly,becoming fertile (containing protoscoleces) in 89 months (Barneset al., 2007a), compared with sheep where the earliest time to fer-tility is approximately 2 years (Slias, 1980). The increased suscep-tibility of hydatid-infected macropodids to predation by wild dogsmeans that wild dogs are catching and consuming a disproportion-ately large number of infected animals which is likely to be a majorcontribution to the high worm burdens seen in many wild dogs.Within all wild dog populations surveyed, a proportion of thesample has been wild dogs with worm burdens in excess of100,000 E. granulosus (Jenkins and Morris, 1991, 2003; Jenkinset al., 2008). These animals are the super spreaders of the popu-lation (Gemmell and Lawson, 1986), ensuring large numbers ofeggs being released into the environment. The home range of wilddogs varies depending on the sex of the animal and availability offood and water; in eastern Australia home ranges average approx-imately 100 km2 (Claridge et al., in press). Therefore large areas canbecome contaminated with eggs from a single animal, but sincepacks of wild dogs consisting of several animals usually occupythese spaces (Claridge et al., in press), contamination of the envi-ronment with faeces can become heavy in areas used commonlyby a resident pack.

The longevity of eggs of E. granulosus in the environment isthought to be several months to perhaps approximately 1 year,so long as the environment is not too hot and dry (Eckert andDeplazes, 2004). However, in a study in Argentina (Thevenetet al., 2005), E. granulosus egg-laden dog faeces were left in theenvironment for 41 months. After this time eggs were separatedfrom the faeces and fed to each of four sheep. Hydatid cysts devel-oped in each of the sheep, suggesting that the longevity of eggs ofE. granulosus in Australia under optimal conditions may be longerthan 12 months. Studies reported in Gemmell (1958) revealedthe most important environmental conditions required for trans-mission for E. granulosus in Australia to be at least 25 mm of rainfor 6 months of the year with temperatures up to 30 C. Conse-quently, E. granulosus has become more prevalent in eastern Aus-tralia, in areas associated with the Great Dividing Range, and inan elevated area of Western Australia (Thompson et al., 1988;Jenkins and Macpherson, 2003) (Fig. 3).

3.7. Echinococcus granulosus in introduced wildlife species

3.7.1. FoxesThe rst creditable report of E. granulosus infection in foxes in

Australia was by Gemmell (1959a) where a single terminalsegment was recovered from the intestine of one of 41 animalscollected in New South Wales. Nevertheless, based on the available

872 R.C.A. Thompson, D.J. Jenkins / Internationaexperimental infection and survey data, Gemmell (1959a) felt thatAustralian foxes were not acting as a denitive host for E. granulo-sus. More recently, E. granulosus have been recovered from anumber of naturally infected foxes in various studies (Thompsonet al., 1985; Obendorf et al., 1989; Jenkins and Craig, 1992;Reichel et al., 1994; Jenkins and Morris, 2003). Almost exclusively,worm burdens have been small, usually less than 50 tapeworms/fox. However, in one study (Reichel et al., 1994) several thousandE. granulosus in each of two foxes from Victoria were reported.These data are so at odds with all other existing fox E. granulosusworm burden data that they should be regarded cautiously. How-ever, if corroborated then the role of foxes in the transmission of E.granulosus may have to be re-evaluated. The current consensus isthat foxes act as denitive hosts for E. granulosus but are of minorimportance in the transmission of the parasite in rural areas ofAustralia. However, foxes infected with E. granulosus are of poten-tial public health importance when infected animals encroach intourban areas (Jenkins and Craig, 1992).

3.7.2. Feral catsInfection of Australian feral cats with adult E. granulosus has

never been reported. Jenkins and Morris (2003) examined theintestines of 23 feral cats collected in an area of high E. granulosustransmission in the local wildlife and none was found infected. Jen-kins also fed protoscoleces recovered from a wallaby to two catsand two fox cubs, and small numbers of E. granulosus were recov-ered from both foxes but nothing was found in the cats (D.J. Jen-kins, unpublished data). It is generally considered that feral catsin Australia are not denitive hosts for E. granulosus.

3.7.3. Feral pigs, goats, deer, horses and rabbitsHydatid disease occurs in Australian feral pigs (Jenkins and

Morris, 2003; Lidetu and Hutchinson, 2007). The study of Jenkinsand Morris (2003) was conducted in south-eastern New SouthWales; 204 pigs were examined, 22.5% contained hydatid cystsand depending on the survey area between 15 and 22% of the cystswere fertile. In contrast, the study of Lidetu and Hutchinson (2007)was conducted in tropical northern Queensland; 74 pigs wereexamined and 31.1% contained hydatid cysts, but the rate of fertilitywas almost three times that of the pigs collected in New SouthWales. The reason for this difference in cyst fertility is unclear. Thereis no doubt feral pigs could contribute to transmission of E. granulo-sus in wildlife but the degree to which they contribute is debatable.Adult feral pigs (the animals most likely to harbour fertile cysts) arebig and strong and difcult for wild dogs to catch and kill; conse-quently, wild dogs mainly predate on piglets, animals least likelyto contain fertile cysts. Inevitably, adult pigs eventually die andtheir carcasses become available for scavenging by wild dogs andfoxes. However, particularly in summer, scavengers would need tond the carcass soon after death before fertile cysts became non-infective due to putrefaction. Therefore, the role of pigs in the trans-mission of E. granulosus in Australian is likely to be minor.

Hydatid infection in goats has never been reported except for ananecdotal report fromWestern Australia (R.C.A. Thompson, unpub-lished data). Periodically, one of the current authors (D.J. Jenkins)has examined small numbers of feral goats, collected from variousareas of south-eastern New South Wales, and has never found anyinfected with hydatid cysts (D.J. Jenkins, unpublished data). Theabsence of hydatid infection in Australian feral goats is curiousbecause in many countries goats are important intermediate hosts(Schantz et al., 1993).

Hydatid cysts have never been reported from feral horses ordeer in Australia. Therefore, until data to the contrary are available,feral goats, deer and horses appear not to be part of the lifecycle ofE. granulosus in Australia.

Rabbits naturally infected with hydatid disease have rarely

rnal for Parasitology 44 (2014) 865877been reported. The two reports, (cited in Gemmell, 1959b) arethought to be a mis-identication of metacestodes of Taeniaserialis. Wild Australian rabbits have been shown to be susceptible

l JouR.C.A. Thompson, D.J. Jenkins / Internationato experimental infection with hydatid disease (Jenkins andThompson, 1995). The cysts established in the lungs and appearedto be developing normally. However, the rabbits were given a largedose of eggs, far higher than anything they would normally beexposed to in the wild, which may have been the reason theybecame infected.

3.8. Current prevalence of E. granulosus in Australian domestic dogs,sheep and cattle on mainland Australia and the island state ofTasmania

3.8.1. DogsThe most recently published study on intestinal helminths in

Australian mainland dogs is that of Palmer et al. (2008) where1400 faecal samples collected in vet clinics were sent to the authorsfor testing. These samples were from urban dog owners with a closeinterest in the health of their pets; unsurprisingly, no taeniidcestodes were identied in any of the samples collected. The mostrecent study of intestinal helminths in rural dogs (Jenkins et al.,2014) screened faeces from 1425 rural dogs living in eastern Aus-tralia (1119 mainland; 306 Tasmania) with faecal otation, molec-ular methods and the E. granulosus coproantigen test (Jenkins et al.,2000). Surprisingly, taeniid eggs in faeces were also uncommon,being recovered from the faeces of only 11 dogs. This is likely tobe because more than 98% of owners reported feeding dry commer-cial dog food exclusively or as a major component of their dogs dietand approximately 50% of owners either de-wormed their dog(s)2 monthly or 4 monthlywith a de-wormer containing praziquantel.Nevertheless, an additional 45 dogs were positive in the E. granulo-sus coproantigen test (1.9% of mainland samples and 7.8% ofTasmanian samples). Some coproantigen-positive faecal sampleswere also positive in an E. granulosus coproPCR (Jenkins et al., 2014).

Fig. 3. Map depicting areas of high, low, rare and no transmission of Echinococcus gratransmission; grey, no transmission). (Modied version of the map published by Jenkinrnal for Parasitology 44 (2014) 865877 8733.8.2. SheepHydatid disease prevalence data are not collected in Australian

abattoirs, but in Tasmania occurrence of infection in livestock ismonitored and traced back to the property of origin. Hydatiddisease still occurs periodically in Australian sheep, howeverthe prevalence has declined steadily during the last 30 years (D.J.Jenkins, personal observations), no doubt a reection of the declineof E. granulosus infection in rural domestic dogs (Jenkins et al.,2014). Sheep populations now most at risk of contracting hydatiddisease are those grazed on pasture abutting national and stateparks and forests containing populations of wild dogs (Graingerand Jenkins, 1996). These wild dogs periodically enter pastures topredate on the sheep but whilst there also defecate, contaminatingthe pasture with eggs of E. granulosus. Nothing recent has beenpublished regarding the prevalence of hydatid disease in mainlandsheep. The most up-to-date data have been collected by theNational Sheep Health Monitoring Program (Animal Health Austra-lia, 2011, http://www.animalhealthaustralia.com.au/programs/dis-ease-surveillance/the-national-sheep-health-monitoring-project/).

Routine monitoring of slaughtered sheep for hydatid infection isstill undertaken in Tasmania. Since the declaration of provisionaleradication in 1996, there have been two reports of infection insheep; one in 2011 in sheep sent to a mainland abattoir forslaughter (Jenkins et al., 2014) the other, more recently in 2013(D.J. Jenkins, unpublished data) in a single animal, resident on aproperty in the midlands area of Tasmania. Investigations haveshown this sheep was imported from South Australia so could havebecome infected before arrival in Tasmania.

3.8.3. CattleHigh levels of hydatid disease in slaughtered cattle have been

reported, anecdotally, from abattoirs in south-eastern Queensland,

nulosus in Australia (red, high transmission; orange, low transmission; beige, rares and Macpherson (2003)).

the northern Queensland beef industry of $6 million per year due

The 24 Tasmanian domestic dogs that tested positive in the E.

l Jougranulosus coproantigen ELISA and the hydatid-infection data fromsheep and cattle found since declaration of provisional freedom in1996 indicate that hydatid disease has not been completely eradi-cated from the island as was previously thought but continues tobe transmitted at low levels (Jenkins et al., 2014).

3.9. Human prevalence

The prevalence of human hydatidosis on mainland Australia isunknown, because in most jurisdictions human hydatid diseasehas ceased to be notiable. The last published data on humanhydatid disease on mainland Australia was that of Jenkins andPower (1996) but these data were only collected in New SouthWales and the Australian Capital Territory and are now out of date.Nevertheless, new cases continue to be identied annually onmainland Australia. A proportion of these new cases are in recentlyarrived immigrants from a range of countries who were infected intheir country of origin. In the study of Jenkins and Power (1996),60% of cases diagnosed in residents living in major urban centreswere recent immigrants. There has been a recent publication onhuman hydatid disease in Tasmania (OHern and Cooley, 2013).The authors described human hydatid disease in Tasmania sincethe declaration of provisional freedom in 1996. Transmission ofhydatid disease to humans in Tasmania has now ceased, althoughone or two new cases are diagnosed annually. However, all of thesenew cases are in elderly people who were thought to have beeninfected pre-1996.

4. Conclusions

Australia has a long history of research on hydatid disease andthe causative agent Echinococcus. Much of this was borne fromnecessity, given the impact the parasite had on public health and

th thto hydatid-infected offal was reported for 2004, with prevalencelevels ranging between 2051% in cattle from coastal areas and3% in those from inland areas (Banks et al., 2006b). The source ofinfection in these cattle is likely from wildlife since cattle are com-monly grazed in areas inhabited by wild dogs because predationimpacts are less severe than if sheep were grazed in the sameareas.

As with sheep, hydatid disease is monitored in slaughtered cat-tle in Tasmania. Since declaration of provisional eradication in1996, over 200 hydatid-infected cattle have been identied. Mostof these animals proved to be imports from the mainland, mainlyGippsland in Victoria, an area where hydatid infection in cattle iscommon. However, 31 were animals less than 3 years old andhad never left Tasmania (Jenkins et al., 2014). DNA was extractedand sequenced from cysts removed from four of the infected cattle;their infections proved to be the G1 sheep strain of E. granulosus(Jenkins et al., unpublished data). The G1 sheep strain not onlyinfects sheep but can also infect cattle, pigs, goats and macropodidmarsupials. Less than 5% of G1 hydatid cysts in Australian cattleare fertile (Kumaratilake and Thompson, 1982), therefore cystsfrom infected cattle, if consumed by dogs, dingoes or their hybrids,commonly do not contribute to transmission of E. granulosus.north-eastern New South Wales and eastern Victoria. No recentdata have been published regarding hydatid disease prevalencein Australian cattle, but according to abattoir management preva-lence is high enough to be causing substantial nancial losses tothe abattoirs through condemnation of offal. An estimated loss to

874 R.C.A. Thompson, D.J. Jenkins / Internationathe agricultural economy in the late 19 and early 20 centuriesin Australia. However, the research that has been conducted inAustralia has contributed much to the international research efforton Echinococcus and hydatid disease, in particular the value of theorganism as a model in studies on developmental biology andepidemiology, not just concerned with Echinococcus but morebroad-ranging in terms of basic biology and theoretical models oftransmission dynamics. We hope that Australia will continue tocontribute to research on Echinococcus and that this will have animpact internationally and sustain the collaborations that havedeveloped with research groups and centres world-wide.

Acknowledgements

We are very grateful to Mark Preston (Graphic Designer, Mur-doch University, Australia) for producing the graphical imagesand to Craig Poynter (Spacial Analysis Unit, Charles Sturt Univer-sity, Australia) for preparing the map. Image of dingo and kangarooincluded on the front cover of this Special Issue is courtesy of theInvasive Animals Cooperative Research Centre, Australia.

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