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27 Cards in this Set
- Front
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Basic nematode characteristics |
•Cylindrical bodies •Have external non-living cuticle •Pseudocoelomate body cavity •As a group, very diverse living habits (parasites, predators, savengers, herbivores) •Occupy virtually all habitats on earth that have been colonized by living organisms •Often incredibly abundant •About 10,000 described species and many thousands more undiscovered |
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Integument |
•Nematodes have a cuticle that is based primarily on the fibrous protein collagen •It is secreted by the epidermis •The cuticle is resistant to physical and chemical degradation •Epicuticle of lipoproteins covers the cuticle •Cortical zone - cuticulin protein layer above a layer of collagen fibers; a tough resistant layer •Basal zone - two or three criss-crossed layers of collagen fibers (gives strength, but allows for streching) •Basement membrane |
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Skeletal system |
•There are no skeletal structures in nematodes •They do have a hydrostatic skeleton, based on fluid pressure in their pseudocoel body cavity ▪maintaining the fluid under pressure gives the body firmness and provides an antagonistic force for the muscles in the body wall to work against |
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Muscular system |
•Nematodes have only longitudinal muscles in their body wall (there are no circular muscles) •As a result, they are capable of only side-to-side "swimming" movements •Muscles work against the fluid pressure of the pseudocoel during their contractions |
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Feeding and digestion |
•Nematodes are mostly liquid feeders. They may be predators, savengers, herbivores, or parasites •The mouth is commonly armed with piercing structures, such as stylets, jaws, or cutting blades •The mouth leads into a short or long pharynx (or esophagus), which may have a muscular bulb to provide suction. Its lumen is triradiate •Beyond the pharynx is a long intestine, which ends in a subterminal and ventral anus |
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Excretion |
•Nematodes have specialized renette cells, which provide for excretory function ▪the renette cell is sac-like, with a duct that leads to the excretory pore •Wastes and water enter the renette cell from the pseudocoelomic fluid, and is emptied through the excretory pore •More advanced nematodes have done away with the sac-like portion, and have only tubules (often in an H-shaped configuration) connected to the excretory pore |
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Reproduction |
•Nematodes are dioecious (separate sexs), and a small degree of sexual dimorphism occurs (body size, male spicules, etc.) •Reproductive systems are variable, although basic components are present in all ▪male system: testes, vas deferens, seminal vesicle, ejaculatory duct, copulatory spicules, cloaca ▪female system: ovaries, oviducts, uterus, vagina, genital pore |
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Life cycle |
•Nematodes have a basic life cycle: ▪egg -> larva1 -> larva2 -> larva3 -> larva4 -> adult ▪larval stages are referred to as instars •Strategies for reproduction: ▪oviparity - egg-laying ▪ovoviviparity - eggs hatch in the female's uterus and larva1 emerges from the female pore. Or the larva hatch as the eggs leave the pore •Change from one larval stage to the next is brought about by molting •Molting is not necessarily accomplished by a great deal of growth |
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Order Trichiurata Family Trichiuridae Trichuris trichiura Human whipworm |
•The name "Trichuris" actually means "thread-tail", which is a misnomer •The head is at the tip of the whip, rather than the tail.
Distribution: •Cosmopolitan in distribution ▪anywhere climate is warm with high rainfall and humidity, lots of shade ▪The eggs are susceptible to dessication •It is estimated that 900 million people in the world are infected •2nd most common nematode parasite in humans in the USA (20-50% infection rates in the southeast) |
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Trichuris trichiura Morphology |
•Adults 30-50mm long, with a long thin anterior region and a thicker posterior end •Males are smaller than females, and usually have a coiled posterior end with a single spicule •The intestine is long and appears beaded (owing to presence of flanking unicellular glands called stichocytes) •The egg (from stool samples) is diagnostic ▪elongate oval 50-54x23u, with a thick, yellowish shell and apical plugs |
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Trichuris trichiura Life cycle |
•Adults live in the lower ileum, caecum, appendix, colon, and rectum, where they burrow into the mucosal lining •After copulation, females produce up to 7000 eggs. •Eggs deposited with the feces into the soil •Eggs contain uncleaved zygotes, and undergo embryonation for 3 weeks in the soil •Two molts occur inside the egg -> produces infective third stage (unhatched) larva •Egg at this stage ingested by the human -> infection •Eggs usually ingested in contaminated food or water, or from contaminated fingers •Eggs hatch in the intestine •Third stage larvae emerge to burrow into the intestinal lining •As they become adults (2 molts), they migrate to the more posterior regions of the gut •The worms are known to live for 4-6 years (one report up to 8 years) |
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Trichuris trichiura Symptomatology |
•Fewer than 100 worms are present, generally no symptoms. •The worms burrow into intestinal lining -> hemorrhages and ulcerations in heavy infections •Symptoms: ▪Nausea, bloody stools, pain in the abdomen, diarrhea, weight loss ▪Rectal prolapse ▪Anemia (probably the result of the worms feeding on blood and/or the hemorrhaging of the mucosa) •Secondary bacterial infections can result. In very heavy infections, it can be fatal |
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Other species of Trichuris |
•T. felis - cats •T. opaca - muskrats •T. discolor - cattle •T. leporis - rabbits •T. vulpis - dogs •T. ovis - cattle and sheep |
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Capillaria spp. Capillaria hepatica |
•Cosmopolitan parasite of rodents and other mammals, that occasionally enters humans
•Rodents ingests the eggs, which hatch in the intestine; the larvae migrate to the liver, the definitive site
•Eggs are deposited in the liver as the female worms wander, and the liver accumulates massed of these eggs
•Humans get infected when they ingest embryonation eggs from contaminated soil, food, or water ▪source of contaminated is the feces of carnivores ▪when carnivores eat infected rodents (livers), the eggs pass through the carnivore's gut without generating infection in the carnivore
•Wandering of the worms in the human liver produces destruction of the liver cells which can lead to death
•The symptoms resemble hepatitis or eosinophilia
•Diagnosis can only be made with liver biopsies. Humans may pass eggs in the feces, but only do so when they eat the livers of infected animals. |
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Capillaria philippinensis |
•An intestinal form found in the Orient
•Its biology is not well known, but human infection may result from eating infected fish and certainly by fecal contamination
•The worms burrow into the intestinal mucosa
•Can produce significant degeneration of the mucosal lining in heavy infections ▪worms can severely affect absorption of nutrients, and can cause emaciation of the host
•Violent diarrhea is also common in heavy infections. It can be fatal
•Eggs of the worm can hatch in the intestine, leading to heavy infections |
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Family Trichinellidae Trichinella spiralis Trichina worm |
•Causes trichinosis (Trichinellosis) in humans •Adults are intestinal parasites of humans and other carnivorous mammals •Unusual life cycle in which the infection is passed among carnivorous mammals Distribution •Most common in temperate regions, in some tropical locations (e.g., Mexico, South American, Africa, Southern Asia) •In the USA, the incidence of trichinosis in adult humans is 4.2%, based on a study in 1973 by Zimmerman, they examined 8000 human diaphragms from 48 states and D.C. |
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Trichinella spiralis Morphology |
•Males 1.4-1.6mm, females about 3mm •Body tapers towards the anterior end; flanking the anus at the posterior end is flanked by papillae •The esophagus is flanked by stichocytes •Males lack copulatory spicules, and the female gential pore is anterior (approx. At a position 1/4 the length of the worm, at the level of the esophagus) •Females have a single uterus |
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Trichinella spiralis Life cycle |
•The life cycle is unusual in that a given host serves both as an intermediate host and definitive host at the same time
•Typical hosts: wild and domestic carnivores, rodents, humans, pigs, etc.
•Predator-prey relationships and cannibalism are important for life cycle
•Pigs, the primary intermediate host in human transmission, get the worms by eating infected rats, pork scraps, or by cannibalism
•The adult worms live in the intestine
•Copulation occurs about a day after infection
•Males die after copulation, and the females burrow into the intestinal mucosa
•The eggs hatch in utero, and the young are released from the female's genital pore (=ovoviviparity) into the mucosa
•The female can produce about 1500 larvae in 4-16 weeks, after which she dies
•The larvae burrow out of the intestine and enter the bloodstream
•They encyst in many tissues, but prefer muscle (especially the muscles of the eye, tongue, masseter, diaphragm and intercostals, and the muscles of the limbs)
•Each larva (first instar?) actually bores into a muscle fibers and causes its degeneration
•The muscle cell becomes a nurse cells
•The cysts are apperently not infective until about 4-8 weeks post-encystment
•Cysts are long-lived -- one report suggests 30yrs
•Life cycle is continued when the host is eaten by a predatory or cannibalistic animal, placing the cysts in that animals intestine
•The worms emerge from then cysts, complete 4 molts (?), and start reproducing after a little more than a day in the host |
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Trichinosis- a zoonosis |
•Trichinosis is regarded as a zoonosis •Humans get the disease primarily from eating raw or poorly cooked infected pork ▪a heavily infected pig can have as many as 100,000 encysted worms/ounce of meat ▪this translates to a meal of pork giving a person a million juveniles that can encyst in the body •Cysts can be killed by thoroughly cooking the meat (pork) -- until no traces of pink meat can be seen |
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Trichinella spiralis Symptomatology |
In severe infections: •Penetration of young adult females into the mucosa -> inflammation and secondary bacterial infection of the intestinal lining, which results in nausea, vomiting, diarrhea, headaches, abdominal pain •Migration of larvae into the bloodstream and to the striated muscles -> periorbital endemia, conjunctivitis, photophobia, fever, chills, sweating, muscle pain and spams, etc. •Depending on where the larvae go, the patient may suffer pleurisy, pneumonia, peritonitis, myocarditis (fatal) •Penetration of muscle fibers -> sharp muscular pains, difficulty in breathing (diaphragm) or swallowing, swelling of the masseter (stimulates mumps) •Eosinophilia is very common and can be helpful in diagnosis, given a history of eating pork •Neurological disorders (when the larvae end up in the nervous system): ▪supraorbital headaches, delirium, stupor, loss of reflexes, mental apathy (stimulates encephalitis, meningitis) •People can die of trichinosis in as little as 2-3 weeks, but usually it requires about 4-8 weeks ▪fatalities result from cardiac or cerebral involvement, pneumonia, pulmonary embolism, kidney failure, or exhaustion |
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Trichinella spiralis Diagnosis and treatment |
•Diagnosis is somewhat more difficult because the worms are small, and they do not pass eggs in the feces •Immunological tests are fairly good, but most cases are probably undetected •Biopsies of muscle tissue can be done, and are effective for demonstrating encysted larvae. •There is no really satisfactory treatment for trichinosis ▪Typically, people are treated with corticosteroids and analgesics to relieve symptoms |
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Trichinella spiralis Other comments |
•Humans can and do get the disease from eating other carnivorous mammals, such as bears •The André expedition to the Arctic in 1897 failed because the men died of trichinosis acquired from eating an infected polar bear that they had killed. •There is some recent evidence that Mozart may have died of trichinosis |
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Order Dioctophymata Dioctophyme renale Kidney worm |
•Large worms that live in the kidneys of carnivorous mammals •Known from Europe, North and South America, China. One text reports it to be common in dogs from North Carolina |
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Dioctophyme renale Morphology |
•These worms are very large ▪Males: 14-40cm long and 4-6cm thick ▪Females: 20-100cm long and 5-12cm thick •The worms are blood-red in color; the cuticle is transversely striated •Males have a small cup-shaped copulatory bursa with slender, straight spicule •The female's posterior end is rounded; the vulva is anteriorly located •The eggs are barrel-shaped, with a pitted shell surface and polar plugs. The measure 66x42u |
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Dioctophyme renale Life cycle |
•Hosts are any carnivorous mammal that eats fish, including dogs, raccoons, mink, etc. •The adults live coiled up inside the kidney (usually the right one, probably because it is the easiest to rechargeable from the stomach and liver) •Sometimes they occur in the body cavity •Eggs are passed in the urine, enter water, and hatch into first instar larvae •The larvae are eaten by a freshwater oligochaete annelid. The annelid may subsequently be eaten by a frog or fish, in which it will encyst •Fish/frogs are eaten by a carnivore and the juvenile excysts in the stomach, penetrates its wall and moves into the liver •From the liver (after about 50 days), goes to the kidney •Other animals (e.g., horses, cattle) can get the infection by eating the annelids in their drinking water |
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Dioctophyme renale Symptomatology and pathology |
•The worms in the kidney destroy the internal structure of the kidney, so that the kidney becomes an empty sac containing the worm •They are usually found only in one kidney (if in both kidneys, the host would quickly die) •They can be removed only surgically •Eggs in the urine, as well as signs of blood and pus in the urine, are diagnostic; however the rarity of the worm makes it unlikely that a doctor would suspect it. |
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Dioctophyme renale Epidemiology |
Infection rates: •2 out of 100 stray dogs in eastern and southeastern USA were found to be infected on a 1965 study •1 in 320 raccoons in SE USA •2of 27 timber wolves in Minnesota were found with the worms |
