echinococcus species species heinz mehlhorn* institut f€ur zoomorphologie, zellbiologie und...

Echinococcus Species

Heinz Mehlhorn*Institut f€ur Zoomorphologie, Zellbiologie und Parasitologie, Universitätsstraße 1, D€usseldorf, Germany

Name

Greek: echinos = hedgehog; kokkos = spherical; the name refers to appearance of the brood capsule.Latin: granulosus = containing granules = tiny slices; multilocularis = forming many empty hollows.English: tiny dog dwarf worm.

Geographic Distribution/Epidemiology

E. granulosus occurs worldwide in all countries with sheep farming. E. multilocularis occurs from Siberiato West Europe until South France; it is also found in Hokkaido (Japan) and focally in North America.E. vogeli occurs in Uruguay. While worldwide only rather few (several thousands) humans are infectedwith E. multilocularis, hundred thousands of humans become infected by E. granulosus in countries withintense sheep farming.

Morphology/Life Cycle

(a) E. granulosus prefers dogs besides foxes as final hosts. The adult worm reaches a length of 2.5–6 mm(Figs. 1, 2, 3, and 4) and possesses mostly only three proglottids, whereby the last one is mostly longerthan the whole anterior portion. The scolex of this worm attaches itself at the intestinal wall by help ofthe four suckers and a rostellum of hooks (consisting of 30–42 small or large hooks that measure either25–40 40 mm or 19–35 mm). Infected final hosts always contain numerous of these worms. The eggsare of the Taenia-type measuring 30–40 40 mm in diameter. They contain when being set free fromdisrupted proglottids already the infectious larva (oncosphera). Different strains of E. granulosusprefer different intermediate hosts (Fig. 5) and have developed slight differences in the appearance ofthe terminal proglottids. If intermediate hosts (sheep, cattle, other ruminants) or humans ingestinfectious oncosphera larvae inside eggs being excreted by final hosts (dogs, foxes; Fig. 1), formationof so-called hydatids occurs, wherein numerous protoscolices (young tape worms) are formedasexually (▶metagenesis) within brood capsules (Figs. 6, 7, 13, 15).

(b) E. multilocularis: This worm prefers as final host foxes besides dogs, and in rare cases cats are alsoinfected (Figs. 2, 8, 9). As adult worm it reaches in general a length of 1.5–3 mm. The last proglottid,which contains the infectious eggs, does mostly not surmount the common length of the anterior 4–5ones (Fig. 2), when being disrupted and discharged within the feces. The scolex is armed by 4 suckers

*Email: [email protected]

*Email: [email protected]

Encyclopedia of ParasitologyDOI 10.1007/978-3-642-27769-6_979-2# Springer-Verlag Berlin Heidelberg 2015

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http://link.springer.com/SpringerLink:ChapterTarget

Fig. 1 Life cycle of Echinococcus species. Life cycles of Echinococcus granulosus (1–8) and E. multilocularis (1.1–8.1.). 1,1.1 Final hosts may be dog, cat, or fox with clear, species-specific preference. 2–3.1 Adult worms, which live in the smallintestine of the final host, may be differentiated according to the size of their terminal ▶ proglottids (P) and shape of uterus(UE) and according to the size of rostellar hooks. 4, 4.1 Eggs containing an infectious▶ oncosphera larva are released from thedetached drying proglottid in the feces of the host; eggs are indistinguishable from those of▶ Taenia species. 5. 5–1 Eggs areorally ingested by intermediate hosts or man with contaminated food. 6, 6.1 Inside the intestine of the intermediate hosts(including man), the oncosphera hatches, enters the wall, andmaymigrate (via blood) to many organs. Cysts are formedmostlyin the liver and lung. In E. granulosus large unilocular ▶ hydatids occur, which are filled with fluid (containing thousands ofprotoscolices), whereas in E. multilocularis a tubular system infiltrates the whole organ (giving rise to alveolar aspects insections). 7 – 8.1 In▶ brood capsules of both cyst types,▶ protoscolices are formed, which may become evaginated (8) eveninside their cysts. Evaginated or not, protoscolices are fully capable of infecting final hosts when they feed on infected organsof intermediate hosts (BC= in▶ brood capsule; EB=▶ embryophore of the egg; EX= excretory vessels; GP= genital pore;H = hydatid; HO = hooks of oncosphera; IR = invaginated rostellar hooks; P = ▶ proglottid; RH = rostellar hooks;SU = sucker; TU = tubular system; UE = uterus containing eggs)


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Fig. 2 Scanning electron micrograph of adult worms of E. granulosus (left) and E. multilocularis

Fig. 3 Light micrograph of a stained adult worm of E. granulosus showing the typical large last proglottids


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and by a rostellum of 26–36 hooks, which includes larger ones (25–29 mm) as well as smallerones (19–24 mm). Intermediate hosts are mainly rodents (e.g., mice, rats; Fig. 1). In these hosts(but unfortunately also in humans), a so-called alveolar cyst is developed from each ingested egg ofthis tapeworm. Inside this cyst (with hollow channels and cancer-like growing undifferentiated cells;

Fig. 4 Macrophoto of an open intestine of a dog containing numerous adult E. granulosus worms

Fig. 5 Diagrammatic representation of the developing terminal proglottids of three strains of E. granulosus from differentintermediate hosts: Kamel = camel; Rind = cattle; Schwein= pig; EL = longitudinal excretion channel; EQ = cross runningexcretion channel; GÖ = genital opening; HO = testis; OT = ootype plus Mehlis’ gland; OV = ovary (germarium);UT = uterus; VO = vas deferens; VI = vitellarium


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Figs. 10, 11, 12, 15), finally young tapeworms (protoscolices) are developed which become sexuallymature, if they are ingested by the final host (fox, dog, cat).

(c) Echinococcus vogeli: This species parasitizes as adult worms in forest dogs (e.g., Speothos venaticus)in Central and South America reaching a size of 2.2–2.9 mm. Intermediate hosts are rodents (Agoutisspecies), cotton rats (Pacas species), and occasionally humans. In the case of humans, a polycysticechinococcosis is introduced.

(d) Echinococcus shiguicus occurs in so-called Tibet foxes (Vulpes ferrilata) in Tibet. Intermediate hostsare pika (Ochotona curzoniae).

(e) Echinococcus oligarthrus occurs in wild cats (jaguar, puma) in Central and South America. Inter-mediate hosts are cotton rats.

Fig. 6 Macrophoto of three closely attached hydatid bladders of E. granulosus from the uterus of a woman

Fig. 7 Macrophoto of sheep liver containing many hydatids of E. granulosus


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Symptoms of Disease (Echinococciasis)

Final hosts mostly show only low-graded symptoms, if at all, so that the danger of human infectionsremains mostly hidden. Only in cases with huge numbers of worms all three species induce catarrhalis orhemorrhagic reactions. In contrast to these low-graded symptoms in final hosts, intermediate hosts areseverely affected and infections may also end fatal, since the liver, brain, lung, and other organs maybecome completely destroyed.

Fig. 8 Scanning electron micrograph of the scolex of E. multilocularis

Fig. 9 Light micrograph of a longitudinal section through an adult worm of E. multilocularis inside the intestinal wall of a fox


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Diagnosis

In infected humans it is needed to detect and define the different cyst types in the infected tissues, sinceonly the hydatids (formed by E. granulosus) can be removed by surgical processes. The detection of allcyst types can be done by computer tomography or sonography or even by help of X-rays. Serological

Fig. 10 Macrophoto of a human liver with an alveococcus of E. multilocularis

Fig. 11 Light micrograph of a section through two protoscolices in a brood capsule in an alveococcus of E. multilocularis


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methods (ELISA, PCR) allow a species determination, which is important, since small cysts may appearrather similar in optic methods. Other serological methods are only successful in 50–60% of lungechinococcosis. The relevant titer in IIFT is 1:320, in IHAT 1:16,000, while ELISA is positive atvalues 1:80.

Infection

Oral uptake of eggs from feces of infected final hosts.

Prophylaxis

Avoid of contact with foxes or foreign stray cats and dogs. Family dogs and cats should be treated withanthelmintics in intervals of about 2 months, in case feed on mice which might be intermediate hosts.

Incubation Period

In humans it takes often years, until tissue cysts are grown up. In final hosts incubation periods are short:4–5 weeks.

Prepatent Period

In final hosts, depending on the species, the prepatent period of E. multilocularis is about 36–38 days andE. granulosus, 35–42 days; in humans, at least 1–2 years.

Fig. 12 Light micrograph of an extruded protoscolex (young worm) of E. multilocularis


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Fig. 13 (a–h) Diagrammatic representation of the asexual development of brood capsules and protoscolices in tissue cystsformed by Echinococcus granulosus. (a) Cyst wall at the beginning of the development (muscle cells are omitted). (b)Invagination of the laminary layer and of parts of the▶ tegument (arrow). (c) Detachment of the invaginated parts. Inside thisnewly formed brood capsule, the laminary material is dissolved, leading to a lumen (DL). (d) Growth of the brood capsule anddivisions of the undifferentiated cells at 2 or 3 sites (only 1 is drawn). (e) Undifferentiated cells protrude into the interior of thebrood capsules. (f) The protrusion starts a lateral growth (arrows). (g) Growth occurs in the direction of arrows withsimultaneous occlusion at the posterior pole. (h) Detached ▶ protoscolex may start evaginating growth (arrow) even withinthe degenerating brood capsule. This process again brings the tegument again onto the outer side of the worm as is required inadult worms (follow the position of the ▶microtriches). AU accumulation of undifferentiated cells, C connective tissue layer,DL developing lumen of the brood capsules, HK rostellar hooks, LL laminary layer, LU lumen of the brood capsule, MTmicrotriches, N nucleus, NU ▶ nucleolus, PA parenchymal cell, PS protoscolex, ST subtegumental cell, SU sucker, TGtegument, TGI tegument interrupted in drawing, UN ▶ undifferentiated cell


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Patency

In final hosts, the patency of E. granulosus is ~7 months and E. multilocularis, 5–6 months; in humans,several years.

Therapy

E. granulosus cysts in humans can be surgically removed. E. multilocularis cysts are mostly inoperable,and thus the patient must be treated for the rest of his/her life by albendazole (12–15 mg/kg bodyweight/daily) or mebendazole (50–60 mg/kg bodyweight/daily). After 2 years it should be tested, whetherparasites have been killed, otherwise treatment has to go on.

Dogs and cats can rather easily be dewormed by application of praziquantel (1� 5mg/kg bodyweight).Their feces should be thoroughly discharged.

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Fig. 14 Diagrammatic representation of the development of the tubelike protrusions of the ▶ alveolar cyst of Echinococcusmultilocularis in tissues of the intermediate hosts in three phases (a–c). (a) At the end of solid strands, undifferentiated cells(UT) fuse with the tegument and thus protrude the strand. At some distance from the tip, hollows (CA) occur inside the strandwhich becomes lined outside by eosinophilic granulocytes (EO) from the host defense system. Arrows indicate direction ofgrowth. (b, c) The hollows (CA) in the strand become larger at the periphery undifferentiated cells (UT) that initiate formationof brood capsules. AS amorphous substance = laminated layer, CA cavity, CN connective tissue, CO ▶ collagen, DCdeveloping cavity, DG degenerating defense cells, DI division of undifferentiated cells, EG eosinophilic granules, EOeosinophilic granulocytes, GR granules, IF infiltration zone of hosts’ defense system. IT intact tissue,Mmembranes of fusingUT,MImitochondrion,MTmicrotriches of the tegument, N nucleus, NH nucleus of the host cell, NU nucleolus, PT protrusionof tegumental surface, TG tegument, U undifferentiated cells, UT undifferentiated cells when fused with the tegument,V vacuole


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Fig. 15 (a–c) Echinococcus protoscolices within brood capsules of ▶ tissue cyst (hydatid, tubular system). (a) Lightmicrograph of a semithin longitudinal section through an inverted protoscolex of E. granulosus. During growth, which maystart to occur inside the brood capsule, the rostellar anlage (RA) protrudes (arrow).�1,000. (b) Scanning electron micrographof already protruded protoscolices of E. multilocularis found inside a brood capsule. �500. (c) Transmission electronmicrograph of an obliquely sectioned inverted protoscolex of E. granulosus. Note the typical tegument lining the surfaceand the invagination through which the ▶ rostellum finally protrudes. �3,000. CA ▶ calcareous corpuscles, E excretorychannel, HK hooks of ▶ scolex, IN invagination, LU lumen of brood capsules, R rostellum, RA rostellar anlage, RE retractedhooks, TG tegument, UN undifferentiated cells, WB wall of brood capsule


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Further Reading

Deplazes P, Eckert J (2001) Veterinary aspects of alveolar echinococcosis: a zoonosis of public healthimportance. Vet Parasitol P8:654–687

Eckert J, Deplazes P (2004) Biological; epidemiological and clinical aspects of echinococcosis: azoonosis of increasing concern. Clin Microbiol Rev 17:107–135

Eckert J et al (1983) Proliferation and metastases formation of larval Echinococcus multilocularis.1. Animal model, macroscopical and histological findings. Parasitol Res 68:737–748

Eckert J et al (2008) Lehrbuch der Parasitologie f€ur die Tiermedizin, 2nd edn. Enke, StuttgartMehlhorn H et al (1981) On the nature of proglottids in cestodes. Parasitol Res 65:243–259Mehlhorn H et al (1983) Proliferation and metastases formation of larval Echinococcus multilocularis.

2. Ultrastructural investigations. Parasitol Res 68:749–763Schweiger A et al (2007) Human alveolar echinococcosis after fox increase in Switzerland. Emerg Infect

Dis 13:878–882Stefanic S et al (2004) PCR for detection of patent infections of Echinococcus granulosus in naturally

infected dogs. Parasitol Res 92:347–351


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echinococcus species species heinz mehlhorn* institut f€ur zoomorphologie, zellbiologie und...

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