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10.1.1.1 Terms Used in Relation to Nematodes
Cuticle\(Cuticula)
The external non-cellular hyaline layer covering the nematode.
Alae
Ridge like extensions of the cuticle. In the anterior region they are known as cervical alae, in the posterior region as the caudal alae.
Papillae
Protuberances on the cuticle. As in the case of alae, these may be cervical or caudal.
Buccal capsule
Is the mouth cavity of the nematode.
Hypodermis (Epidermis)
Alayer between the cuticle and the somatic musculature.
Bacillary band
Arow of longitudinal cells formed by the hypodermis. Seen inTrichinelloidea.
Coelomyarina
Somatic muscle cells in which the muscle fibers extend along the sides of the cell in addition to lying perpendicular to the hypodermis.
Platymyarian
Somatic cells in which the muscle fibers lie only perpendicular to the hypodermis.
Meromyarian
Anematode in which few muscle cells are seen between chords; e.g., Enterobius and hookworms.
Polymyarian
A nematode in which many muscle cells are seen between chords; e.g., Ascaris, filarial worms and Dracunculus.
Amphid
Sensory receptors situate near the posterior end of the nematode.
Phasmid
Sensory receptors situated near the posterior end of the nematode.
Spicule
The male copulatory organ which is elongated and protrusible. Its length, shape and number vary in different species.
Copulatory bursa
A membranous expansion of cuticle at the posterior end of certain nematodes. It is supported by rib-like structures known as rays and is used for holding the female during copulation.
Gubernaculum
A protuberance on the wall of cloaca. It apparently guides the spicule during copulation.
Cloaca
Common opening for the rectum and the genital tract.
Stichosome
Glandular cells (stichocytes) arranged in a row along the esophagus. Seen in Trichinelloidea.
Pseudocelom (Pseudocoel)
Body cavity of nematode which is filled with fluid and in which the internal organs are suspended.
Oesophagus (Pharynx)
The part connecting the buccal capsule to the intestinal tract.
Corpus
Anterior portion of the oesophagus. In Rhabditis type it is divisible into procorpus and metacorpus.
Isthmus
Middle portion of the oesophagus.
Bulb
Posterior portion of the oesophagus.
Didelphic (bicornate)
Having a double set of reproductive system.
Monodelphic
Having a single set of reproductive system in the female nematode.
Viviparous (Larviparous)
Aspecies which discharges larvae instead of eggs.
Ovoviviparous
Discharge larvated eggs
Oviparous
A species which discharges eggs in one cell or morula stages.
Parthenogenesis
Reproduction without fertilization of the ovum by the sperms.
Autoinfection
Self infection with the parasite.
Retroinfection
A form of autoinfection in which the larvae hatch out near the anus and migrate back into the large intestine to develop into adults.
Rhabditiform larva
Is a larva with a short oesophagus, which has a bulb at its posterior end.
Filariform larva
Is a larva with an elongated oesophagus which does not have a bulb at its posterior end.
Paratenic host
Is a transport host in which the particular parasitic stage does not grow, but remains viable.
Periodicity
Term used to denote the presence or absence of microfilariae in blood.
Nocturnal periodicity
When microfilariae show a pronounced peak during nighttime. The rest of the period they are absent or scanty.
Diurnal periodicity
When microfilariae show a pronounced peak during daytime. The rest of the period they are absent or scanty.
Subperiodicity
When microfilariae are present in appreciable numbers throughout the 24-hour period.
Innen-Korper (Inner body)
And elongated structure seen in the mid region of microfilaria. This along with the pharyngeal thread is regard as the modified intestine of the later developing larval stages.
R cells
Embryonic rectal cells seen in microfilaria.
G cell (GI or RI cell)
A large cell close to innenkorper seen in microfilaria. A part of the future intestine.
10.1.1.2.1 Phylum: (Nemathelminthes)
Include all round-bodied worms, commonly referred to as roundworms, or nematodes. Usually cylindrical and elongate in shape. An alimentary canal is present. With few exceptions, the sexes are separate. Body unseqmented. Life cycle may be direct and/or indirect.
10.1.1.2.2 Morphology
The body is covered with a thin cuticle which is secreted by a noncellular hypodermis. The cuticle may be smooth with fine transverse striations or with other adornments. These includes cuticular blebs or wart-like elevations, longitudinal ridges along the sides, epaulets and condons, lateral expansions (either anterior or posterior alae), and various kinds of papillae, spines and, hooks. Beneath the hypodermis are muscle cells. Within the hypodermis are 4 longitudinal thickening, the chords which are called dorsal lateral and ventral chords. They contain the nuclei of the cells which make up the hypodermis. Several fiber layers above the hypodermis have been described which travel in many directions. Muscles are of two types. Somatic or unspecialized and specialized somato esophagus muscle and somato-intestinal muscles. Corpulatory muscles are present (in males): Bursal muscles, spicular muscle, (female) vulvar muscles etc.
The alimentary canal consists of a simple tube (mouth, esophagus, Intestine and anus). The mouth in some species may be well to poorly developed and in some genera provided with teeth, cutting plates or external and/or internal crowns.
The Reproductive system is usually will developed. In the male it consists of a muscular ejaculatory duct followed in succession by the seminal vesicle, sperm duct and filamentous testes. In most species the males are provided with a posterior cuticular expansion supported by rays (two web-like hands) to grasp the female during copulation. This group (strongylina) is the bursate type. The posterior end of other males are blunt or pointed and are provided with finger-like papillae for tactile purposes etc. as well as caudal alae. The posterior end of the female is pointed or near blunt. The female is much larger than the male. The female reproduction organs are as follows: The ventrally located vulva opens into the vagina which gives rise to 1 or 2 uteri, occasionally four. These may arise directly from the vagina and extend posteriorly, or there may be an anterior and a posterior uterus followed in each case by oviduct and a filamentous ovary.
10.1.1.2.3 Reproduction
Reproduction is by means of eggs from the female which are fertilized by amoeboid sperms from the male during copulation. After eggs are fertilized a membrane is formed on its outer surface. This membrane forms the shell proper and thickens as the egg pass down to the uterus. This inner-most layer is termed the viteline or lipid layer which contains some protein and lipids. The middle layer is termed the "chitinous" layer and is composed or chitin, protein and lipids. It is transparent and smooth. The outer-most layer is the Protein layer lipoprotein). It may be thick, smooth, granular, mamillated (bumpy lumpy) or rough depending, upon the amount of protein present, (typically ascarid type). The three layers mentioned above are easily recognized in ascarid eggs in which the protein layer is greatly thickened, however, sometimes this may be lost or missing ("decorticated") exposing the smooth chitinous layer. Only one group of parasitic nematode ova may continue their development without being fertilized by the sperm of the male (Strongloides). All eggs eggs begin their development as, unicellular forms (one-cell stage) from the germinal layers of ovaries and remain in this stage after fertilization in the female worm and gut of the host only in ascaridina and Trichuridae. Further cell division (strongylina) or larvae development within the female worm after fertilization. The stage of embryonic development of parasite ova found in fresh fecal specimens varies among nematode species; thereby constituting an important criterion in diagnosis.
10.1.1.2.4 Helminth larvae: (First stages)
- 1. Tapeworm: hexacanth embryo, Onchosphere - Coracidium
- 2. Flukes: miracidium
- 3. Acathocephals: acanthor
- 4. Nematodes
10.1.1.2.5 Categories
Categories of nematodes based on the stage of development of eggs at the time they are layed by the female worm.
1. Oviparous
Those worms which lay undeveloped eggs (eggs perhaps by to morula stage).
2. Ovoviviparous
Those worms which lay eggs containing fully or near fully developed larvae. Such eggs are said to be "larvated" or "fully embryonated" when layed. Such eggs may even hatch while still in the body of the host - thus larvated eggs or hatched larvae may pass in the stool of the host eggs with vermiform larva.
3. Viviparous
Actually means giving birth to living young (and technically implies the presence of a placentas). Of course, worms do not have a placenta but for some worms the eggs become larvated and actually hatch while retained in the female worm's body. Thus the worm expels living active larvae and the term viviparous, though not completely correct, is applied to these worms. The term larviparous is also used.
10.1.1.2.6 Basic Development
Basic Development Cycle for Nematode larvae:
The original egg divides in two, then four, then eight, etc. It passes through a morula stage and then a "tadpole stage" and eventually becomes a fully formed larva ready to hatch.
If the infective stage for a nematode is a larva, it is usually the third stage (L3) larva. If the infective stage is an egg, the larva within the egg is the second stage (L2) larva.
Nematodes may or may not have an intermediate host. If there is no intermediate host, the life cycle is said to be direct. (For example, L3 hookworm larvae enter the host via skin penetration. There is no intermediate host). If there is an intermediate host, the life cycle is indirect. (For example, Dirofilaria immitis larvae develop within a mosquito. The mosquito is an intermediate host.)
10.1.1.3.1 Order: Rhabditida
Nematodes with rhabditiform esophagus - many are free - living or parasites of lower animals? Only the following genera are important (Numbered in accordance to importance):
- 1) Strongyloides include very important species - females are parthenogenic,
- 2) Micronema - has been identified in nasal tumors, maxillary granulomas, brain and kidney of horses, brain of child, and
- 3) Rhabditis - mostly in sea water, fresh water, or soil, one species cause skin lesions in dogs.
1. Suborder: Strongylata
Males with caudal, usually large, copulatory bursa supported by rays. Produce mostly strongyle types eggs. Have direct life cycle.
a. Superfamily: Trichostrongyloidea
Mostly in the gastrointestinal tract of ruminants; have poorly developed mouth cavity.
Genera:
Trichostrongylus, Ostertagia, Haemonchus, Mecistocirrus Cooperia, Nematodirus, Ollulanus, Dictyocaulus all are fairly to very important. Many are very small.
b. Superfamily: Strongyloidea
large stout bodies with well developed mouth cavity.
1) Family Strongylidae
a) Subfamily Strongylinae
- Buccal capsule large with leafcrowns around opening/bursa large.
Genera:
- 1. Strongylus - large strongyles
- 2. Triodontophorus
- 3. Oesophagodontus Small strongyles
- 4. Craterostomum
b) Subfamily Cyathostominae
Buccal capsule smaller than above group, but similar (small strongyles)
Genus: 1. Cyathostoma
c) Subfamily:
Oesophagostominae - with transverse cervical groove and with cephalic inflation reduced buccal cavity in large intestine of ruminants.
Genera:
- 1. Oesophagostomum
- 2. Chabertia
c. Superfamily: Ancylostomatidea
"Hookworms"-stoma guarded with teeth or cutting plates. Buccal capsule well developed - small intestine.
1) Subfamily: Ancylostominae - with teeth
2) Subfamily: Bunostominae - with cutting plates instead of teeth.
Genera:
- 1. Bunostomum
- 2. Necator
- 3. Globocephalus
- 4. Bathmostomum
- 5. Grammocephalus (in elephants and rhinoceroses).
3) Family: Stephanuridae
With cup-shaped buccal cavity directed straight forward - in renal tissues.Genus: Stephanurus
4) Family: Syngamidae
Large cup-shaped buccal capsule in upper respiratory tract-in permanent copula*Genera:
- 1.*Syngamus
- 2.*Mammomonogamus
- 3. Cyathostoma
d. Superfamily:
Metastrongyloidea - In respiratory vascular and nervous systems of mammals - snails act as intermediate host for all except genus metastrongylus in swine in which earthworms serve in this capacity. Filaroides has direct life cycle.
1) Family: Metastrongylidae
In air passages of swine- eggs larvated.Genus: Metastrongylus
2) Family: Protostrongylidae
Oviparous - eggs developed and hatch before passing in feces.Genera:
1. Protostrongylus
Sheep and goats in bronchioles
2. Muellerius
In parenchymal nodule in sheep and goat
3. Parelaphostrongylus
In meninges of deer
3) Family: Filaroididae
In lungs of canine and feline - much reduced copulatory bursal lobes to papillae. Thin-shelled larvated eggs hatch in host - life cycle direct.Genus: Filaroides in canine.
4) Family: Crenosomatidae
Life cycle involve snails and slugs/well developed bursa. The shell larvated eggs hatch in host.Genera:
- 1. Crenosoma - in canine
- 2. Troglostrongylus - in cats
5) Family: Angiostrongylidae
Bursa reduced, typical strongyle typeGenera:
1. Aelurostrongylus
Oviparous females lay unsegmented eggs in parenchyma of lungs that develop to larvae here - The nest cause inflammation and nodule (in cats).
2. Angiostrongylus
In lung and blood vessels
3. Gurltia
In leptominegeal vein of S. American cats
10.1.1.3.2 Order: Ascaridida
Possess three large lips; caudal alae when present are laterally placed.
1. Superfamily: Oxyuroidea
Are "pinworms" - inhabit the rectum and anus - 3 lips- bulb-like hour-glass esophagus - most are small.Genera:
- a. Oxyuris is equine - long tapering females - asymmetrical single operculated egg-adult females up to 6" long.
- b. Enterobius in man - great apes
- c. Skrajabinema in sheep - eggs fully embryonated when deposited by females.
- d. Passalurus in cecum and colon of rodents - (rabbits hares)
2. Superfamily: Ascaroidea
Mostly large nematodes of the intestine - with 3 lips. No buccal capsule - Tail of female blunt, of male often bent; life cycle, most direct - few indirect.a. Family: Ascaridae
"Ascarids" all large - eggs unicellular and thick-shelled-life cycle direct in most species affecting the usual host of veterinary importance - found in small intestine.
Genera:
- 1) Toxascaris with cervical alae in canine and feline
- 2) Parascaris in equine
- 3) Ascaris in pig, man, raccoon 41 cm long
3. Superfamily: Anisakoidea
With either of the following structures at base of esophagus: Posterior granular ventricles (Neoascaris Now Toxocara) Posterior granular ventriculus and anterior caecum (Porrocaecum-contracaecum).Genera:
- 1) Toxocara in canine feline cow-with cervical alae
- 2) Porroceacum in ducks indirect life cycle
- 3) Contracaecum in water fowl indirect life cycle
4. Superfamily: Neterakidae - parasites of birds
Genera:
- a. Ascaridia in small intestine of fowl with preanal sucker eggs ovoid-shell not as thick as those of above genera ("ascarids" of fowl 72-116mm long).
- b. Heterakis in cecum of fowl similar to ascaridia of fowl but smaller, 10-15mm long.
10.1.1.3.3 Order: Spirurida
1. Superfamily: Dracunculoidea
a. Family: Dracunculidae
In subcutis of man, especially in Africa and Asia; crustacean intermediate host - species in dogs in USA of little importance.
Genus:
Dracunculus - 60-80 mm females, ovoviparous
2. Superfamily: Spiruroidea
Stomas well developed - eggs fully embryonated when laid.a. Family:
Thelaziidae - under eye lids of birds and mammals.
Genera:
- 1) Oxyspirura in eyes of poultry - cockroach is intermediate host
- 2) Thelazia in eyes of livestock and other mammals flies (Fannia, musca) serve as intermediate hosts.
- 3) Spirocerca in nodules of stomach and esophagus canine red in color. During beetle intermediate host.
- 4) Ascarops in stomach of swine Dung beetles intermediate host
- 5) Physocephalus in stomach of swine life cycle involve Dung beetle.
- 6) Simondsia - in pigs in Europe-Posterior past of worm globular
- 7) Gongylonema in esophagus stomach of ruminants fowl-cuticle with blebs.
b. Family: Spiruidae
In esophagus stomach and intestine of vertebrates; Ovoviviparous.
Genera:
Habronema - in stomach of equine - flies (musca, stomoxys) as intermediate host (Draschia).
c. Family:
Acuraidae - anterior part of body ornamented with "condons" cuticular ridges or grooves or epaulette-like thickenings. In gizzard, proventriculus, esophagus or crop of birds.
Genus:
Acuria - in gizzard of foal.
d. Family:
Tetrameridae - related to acuria but have no condoms marked sexual dimorphism, males being while and filiform and tail end of female globular or coiled.
Genus:
Tetrameres in proventriculus of fowl - female blood red color.
e. Family: Physalopteridae
Cuticle usually forms a collar- like projection around anterior extremity; Larvated eggs; beetles are intermediate host.
Genus:
Physaloptera - in stomach of canine and feline.
f. Family: Gnathostomatidae
With large trilobed lips; looks look ridges on inner surface interlock with those opposite lip.
Genus:
Gnathostoma with above characteristics and head - bulb around lips (donut-like) which is armed with 6-11 transverse rows of hooks flat cuticular spines on anterior part of body - in stomach of dogs, cat mink.
3. Suborder: Filariata
a. Superfamily: Filaroidea
1) Family: Fillariidae
long and relatively thin worms which inhabit body cavities, blood, lymph vessels, and connective tissues of their hosts; viviparous females produce microfilaria which utilize vectors as intermediate hosts.
Genera:
- a) Dirofilaria in heart - subcutis eyes in dog, cats, raccoon most important species in dogs.
- b) Dipetalonema - in subcutis of canine and peritoneal cavity.
- c) Stephanofilaria in skin of cattle where it causes a dermatitis
- d) Setaria - in peritoneal cavity of cattle, equine.
- e) Elaeophora in arteries of sheep cattle, deer, zebu-large microfilaria block terminal capillaries causing dermatitis in pole and face region of sheep in USA.
- f) Onchocerca - in connective tissue where the species cause nodule formation.
- g) Brugia - in lymphatics of man monkey - cats - dogs.
- h) Wuchereria well known species causes elephantiasis in man - in lymphatics.
- i) Parafilaria - worms cause connective tissue nodules in equine of eastern countries - nodules frequently bleed.
- j) Mansonella - Peritoneal membranes of man in South American
- k) Sulifilaria - in pig of S. Africa - subcutis
10.1.1.3.4 Order: Trichocephalida Enoplida
1. Suborder: Trichurata
Nematodes with muscular tissue of the esophagus much reduced - stichostome esophagus which consist of a capillary tube surrounded by bodies of single file column of gland cells; one or no spicule in males. Important families are follows:
a. Family: Trichinellidae
Viviparous - host may serve also as an intermediate host - no spicules or copulatory bursa only one genus of importance.
Trichinella - in small intestine of man pig rat and other mammals - larvae in muscle of hosts.
b. Family Trichuridae
Anterior part of worm greatly reduced - long and slender - "whipworms" medium size - ceca, hind end of males coiled-spicule single with protrusible sheath.
Genus:
Trichuris in man, pig, dog, ruminants. Double plugged eggs.
c. Family: Capillariidae
Trichurata in which the anterior and posterior part of body of equal thickness.
Genera:
- 1. Capillaria - species in intestine, liver, lungs and bladder- double plug - eggs.
- 2. Trichosomoides in urinary bladder of rats - double plug eggs male lives inside uterus of female.
- 3. Anatrichosoma in nasal mucosa of African monkeys.
2. Suborder: Dioctophymata
a. Family: Dioctophymidae
Alimentary canal attached to abdominal wall by suspensory muscles - tail of male bears terminal cup-shaped bursa out rays and single spicule - eggs have thick pitted shell except at pole.
Genera:
- 1) Dioctophyma - largest nematode known - 1 meter - red in color and kidneys and peritoneal cavity of canine pole cat, mink, other, beech martin, pin martin and weasel.
- 2) Hystrichis - aquatic birds in glands of proventriculus - cause nodules.
- 3) Eustrongylides in intestine of anatine birds of Europe.
