NUTRITION AND EXCRETION/SECRETION IN PARASITESPart 2: Nematodes

PART 2: NUTRITION IN NEMATODES

Nematoda possess a recognizable and complete alimentary system

Digestive system of nematodes comprised of 3 components

1) Stomodaeum 2) Intestine3) Proctodaeum In a small number of insect parasitic nematodes,

the alimentary canal can be lost completely, under which conditions the exposed hypodermis of the cuticle becomes the site for nutrient acquisition le.g. Mermis, Bradynema).

MORPHOLOGY OF A TYPICAL NEMATODEMALE AND FEMALE

STOMODAEUM

Comprised of mouth, labium, buccal cavity and pharynx

The mouth is usually a circular opening surrounded by a maximum of six lips.

Few parasitic nematodes possess as many as six lips; in some nematodes lips fuse in pairs to form three.

In many species lips are absent altogether,

A buccal cavity lies between the mouth and esophagus of most nematodes.

The size and shape of this area vary among species and are important taxonomic characters.

Food ingested by a nematode moves into a esophagus, or pharynx.

This is a pumping organ that sucks food into the alimentary canal and forces it into the intestine.

Such an arrangement is necessary because of high pressure in the surrounding pseudocoel.

The esophagus a variety of shapes, depending on the order and species of nematode, and for this reason it is an important taxonomic character.

It is highly muscular and cylindrical and often has one or more enlargements (bulbs).

The lumen of the esophagus is lined with cuticle,

Food particles, small enough to pass through the buccal cavity, are drawn into the lumen of the metacorpus by sudden dilation of the procorpus and metacorpus (a). Closure of the lumen of the esophagus in these regions expels excess water (b), and the mass of food particles is passed backward along the isthmus (b, c).Food is drawn between the bulb flaps of the posterior bulb by dilation of the haustrulum, which inverts the bulb flaps (a) and is passed to the intestine by closure of the haustrulum and by dilation, followed by closure of the pharyngeal-intestinal valve (b). Bulb flaps contribute to the closure of the valve in the posterior bulb and, when they invert (a), also crush food particles.

VARIATIONS IN ESOPHAGI IN SPECIES OF ASCARIDOID NEMATODES

Nematodes shown are of genera (a) Crossophorus, (b) Angusticaecum, (c) Toxocara, (d) Porrocaecum, (e) Paradujardinia, ( f ) Multicaecum,(g) Anisakis, (h) Raphidascaris, (i) Contracaecum. v, ventriculus.

INTESTINE

The intestine is a simple, tube like structure extending from esophagus to proctodaeum.

Constructed of a single layer of intestinal cells.

In females a short, terminal, cuticle-lined rectum runs between anus and intestine.

In males the rectum receives products of the reproductive system into its terminal portion cloaca.

The intestine is nonmuscular.

Its contents are forced posteriorly by action of the esophagus as it adds more food to the front end of the system and perhaps by locomotor activity of the worm.

Internal pressure in the pseudocoel flattens the intestine when empty.

Between the dorsal wall of the cloaca and the body wall is a powerful muscle bundle called depressor ani.

When it contracts, the anus is opened;

Hydrostatic pressure surrounding the intestine causes defecation when the anus is opened.

Hydrostatic pressure expels feces with some force

The wall of the intestine consists of microvilli

Several digestive enzymes have been identified in intestinal lumen,

Intestinal digestion is probably of minor importance in most forms because of rapid rate of food movement through the intestine

The intestine functions by digesting, absorbing water and nutrients, and eliminating the residues of digestion.

Cross section of intestine showing microvilli (M) of dorsal and ventral sides.Cellular debris fills the lumen (L)

PROCTODAEUM

Comprised of rectum and anus Covered by a layer of cuticle The proctodaeum serves as the anus and is where waste is

excreted

STRUCTURE AND FUNCTION OF THE FEEDING APPARATUS

Feeding apparatus has been a widely used term for the stoma or mouth in describing nematode feeding mechanisms

A feeding apparatus may be classified into four types:

1. Engulfing2. Piercing3. Cutting4. Sucking

ENGULFING

Only mononchid predators possess this type of feeding apparatus

Engulf and swallow their prey whole, although they may also feed by first shredding prey

The engulfing type consists of two sets of three plates each located in the buccal cavity

A. Feeding apparatus of Anatonchus tridentatus. B. A. tridentatus engulfing Panagrellus redivivus. C. Prionchulus punctatus engulfing an entire prey. D. A. tridentatus ingesting body contents of P. redivivus.

PIERCING

Species with this type of feeding apparatus are known as stylet-bearing nematodes.

The main feature of the feeding apparatus is a protrusible stylet or spear, which is pointed and needle-like with a narrow lumen connected with the oesophagus.

Used to pierce plant or fungal cells and suck fluids, but is also found in some predators, as well as insect and animal parasites.

A. Second-stage juvenile of Heterodera schachtii feeding from the initial syncytial cell in the root of Brassica napus.

B. Xiphinema diversicaudatum penetrating meristematic cells at

the root tip of Ficus carica seedlings. Arrows show feeding site

CUTTING This type of feeding apparatus is present in diplogasterid,

actinolaim and enoplid predators and some animal parasites (e.g. Haemonchus).

Consists of a buccal cavity armed with a tooth or teeth of variable sizes located at different positions on the dorsal and ventral walls.

Cutting and shredding food into pieces or ripping off tissues depends upon the size and number of teeth.

There may be one (e.g. Haemonchus contortus), three (e.g. Ternidens deminutus) or six teeth (e.g. Streptopharagus pigmentatus) with sharply pointed (e.g. Triodontophorus) or rounded tips (e.g. Strongylus vulgaris) or with elaborate ridges (Strongylus asini).

Strongylus vulgaris

SUCKING

The sucking type of feeding is characteristic of bacterial and carrion feeders.

Included in this category are Thelastoma, Mermis, Steinernema and Heterorhabditis (insect-parasitic nematodes) and Chromodora (marine nematode).

The ingestion of nutrients depends upon the concentration and flow of nutrients, turgor pressure at the food resource and suction generated by the median oesophageal bulb.

E.g Ascaris – suck the contents in the lumen.

The mouth opening is surrounded by three lips as shown in this scanning electron micrograph. There is one dorsal lip (A) and two ventro-lateral lips (B) The yellow arrows point to rows of tiny denticles on the inner surface of each lip.

Ascaris mouth opening

NEMATODES GROUPS BASED ON FEEDING

Fungal Bacterial Predacious Unicellular eukaryote Insect Omnivorous Animal Plant

ANIMALS

Food of nematodes parasitic in animals includes blood, tissue cells and fluids, intestinal contents, or some combination of these.

Some species parasitic in the intestine feed only on tissue and not on blood or host ingesta.

Can be classified into several different groups:1) Eats up whatever is present in the intestine2) Eats up liquid tissues/ blood

EATS UP WHATEVER IS PRESENT IN THE INTESTINE

Family Ascarididae - e.g – Ascaris sp. - its main food is liquid contents of the intestinal

lumen - e.g Toxocara canis - Three lips are present

SCANNING ELECTRON MICROGRAPH OF TOXOCARA CATI

Note the three lips with sensory papillae and broad alae at each side.

EATS UP LIQUID TISSUES/ BLOOD

Family Trichuridae- e.g Trichuris trichiura

- The mouth is a simple opening, lacking lips. - The buccal cavity is tiny and is provided with a

minute spear. - The esophagus is very long, occupying about

two-thirds of the body length, and consists of a thin-walled tube surrounded by large, unicellular glands, or stichocytes.

- With their anterior ends buried in mucosa, worms feed on cell contents and blood

Family Capillariidae - e.g Capillaria hepatica - parasite of the liver - causes loss of liver cells Family Trichinellidae - e.g Trichinella sp. - a short muscular esophagus - Adults are intramulticellular parasites in intestinal

epithelium - juveniles reside in nurse cells - juveniles absorb

their nutrients from their enclosing nurse cell

SCHEMATIC DRAWING OF AN INTACT NURSE CELL-PARASITE COMPLEX, SHOWING THE SURROUNDING CIRCULATORY RETE

Family Ancylostomidae - Members of this family are commonly known as

hookworms - They live in their host’s intestine, attaching to the

mucosa and feeding on blood and tissue fluids sucked from it.

- The buccal capsule is large and usually is armed with cutting plates, teeth, lancets, or a dorsal cone.

- Lips are reduced or absent - They have a multi-protease cascade to digest host

hemoglobin. - e.g Ancylostoma caninum, Necator americanus,

Ancylostoma duodenale

Note the two broad cutting plates in the ventrolateral margins (top).

The mouth of Necator americanus.Ancylostoma duodenale,

* Patients with heavy infections may lose up to 200 ml of blood per day

HOOKWORM ATTACHED TO INTESTINAL MUCOSA.

Notice how the ventral tooth in the depth of the buccal capsule lacerates the host tissue.

Family Trichostrongylidae - Are small, very slender worms, with a

rudimentary buccal cavity in most cases. - Lips are reduced or absent, and teeth rarely are

present. - The cuticle of the head may be inflated. - e.g Haemonchus contortus, Ostertagia spp,

Trichostrongylus spp.

Scanning electron micrograph of Ostertagia ostertagia

Family Onchocercidae - live in tissues of amphibians, reptiles, birds, and

mammals. - e.g - Wuchereria bancrofti, Brugia malayi,

Onchocerca volvulus, Loa loa, Dirofilaria immitis, Mansonella perstans

Wuchereria bancrofti

PLANTS

Nematodes feeding on plants are stylet-bearing, obligate parasites obtaining nutrients from living cells of roots, stems or leaves.

Variations in nematode feeding habits occur for their adaptive needs.

Nutrients from living cells and tissues are sucked into the oesophagus through the stylet lumen

Some species, stylet is a tooth that lacks a lumen and is used only to puncture the plant cells

Can be divided into several groups:1) ectoparasitic - Ectoparasitic plant feeders obtain nutrition from

epidermal (e.g. Tylenchorhynchus) or endodermal cells (e.g. Trichodorus, Xiphinema); Psilenchus, Tylenchus and Atylenchus feed only on root hairs

- Ectoparasites, such as the root lesion nematode Pratylenchus, feeds on epidermal cells or on root hairs.

ii) migratory ectoparasiticiii) migratory endoparasitic - Pratylenchus, Anguina, Radopholus and other migratory

endoparasitic species obtain nutrition from cortical cells through periodical intercellular migration within the root.

iv) sedentary ectoparasitic - The sedentary ectoparasite Criconemella xenoplax feeds at a

single feeding site on epidermal cells for long durations, causing little tissue damage, although terminal galls are induced when feeding occurs at the root tip.

v) sedentary endoparasitic; - The sedentary endoparasites, such as Heterodera, Globodera,

Meloidogyne or Sphaeronema, establish complex feeding relationships with their host by modifying host endodermal cells into specialized feeding structures, such as giant cells, syncytia or nurse cells.

vi) semi-endoparasitic nematode categories. - Hoplolaimus and Telotylenchus are semi-endoparasites feeding

internally and externally on plant root tissues.

A. Paratrichodorus anemones feeding on the root hairs of Nicotiana tabacum.B. P. anemones feeding on epidermal cell of N. tabacum. C. Cross-section of root showingfeeding by Meloidogyne incognita on a giant cell. D. Cross-section of tomato root showing gravid M. incognita female feeding on a giant cell. E. Pinewood nematode, Bursaphelenchusxylophilus, feeding on fungal hyphae. F. Lesion nematode, Pratylenchus penetrans,ectoparasitic feeding behaviour on the root hair of tobacco. Arrows show site of feeding

SECRETORY-EXCRETORY SYSTEM

So-called excretory systems have been observed in all nematodes except Trichinellida and Dioctophymatida, but an excretory function was assigned to the systems in various nematodes solely on a morphological basis; that is, the systems simply looked like excretory systems.

The actual functions of these systems vary according to the species of nematode and its stage of development

There are no flame cells or nephridia

The two basic types are glandular and tubular

The glandular type is typical of free-living groups and may be involved in secretion of enzymes, proteins, or mucoproteins.

Several varieties of tubular excretory systems occur.

EXCRETORY SYSTEMS

(a) Single renette in a dorylaimid; (b) two celled renette in Rhabdias spp.; (c) larval Ancylostoma spp.; (d) rhabditoid type; (e) oxyuroid type; ( f ) Ascaris spp.; (g) Anisakis spp.; (h) Cephalobus spp.; (i) Tylenchus spp.

Basically, two long canals in the lateral hypodermis connect to each other by a transverse canal near the anterior end.

This transverse canal opens to the exterior by means of a median ventral duct and pore, the excretory pore.

This pore location is fairly constant within a species and therefore is a useful taxonomic character.

Ultrastructure of the gland cells clearly suggests secretory function.

Enzymes responsible for exsheathment (shedding the old cuticle at ecdysis) are produced there by various strongyle juveniles.

A variety of nematodes excrete substances antigenic for their hosts through the S-E pores.

In Nippostrongylus brasiliensis digestive enzymes were secreted by adult to act in conjunction with the abrading action of the cuticle.

The major nitrogenous waste product of nematodes is ammonia

E.g In normal saline, A. suum excretes 69% of the total nitrogen excreted as ammonia and 7% as urea.

- Under conditions of osmotic stress, these proportions can be changed to 27% ammonia and 52% urea.

Amino acids, peptides, and amines may be excreted by nematodes.

Other excretory products include carbon dioxide and a variety of fatty acids.

The fatty acids are end products of energy metabolism