11. Nematodes (infective eggs) Flashcards
which nematodes are infective in the egg stage?
Trichuris truchiura
Ascaris lumbricoides
Enterobius vermicularis
what is the comon name for Trichuris truchiura?
Human whip worm
what is important to remember in terms of morphology about Trichuris trichiura?
- the adult worm shape: looks like a whip
- the egg hallmark character: bipolar plugs
what rank is Trichuris trichiura in terms of occurence?
third most common nematode of humans
where is T. truchiura found globally? and among who?
- around the world
- more frequent in tropical whether-zones with poor sanitation practices
- children are more prone because they play in dirt and the eggs are found in dirt
how did they know about coevolution with T. trichiura and that it was in prehistoric humans?
they found petrified eggs in prehistoric humans
what is the cat whipworm?
Trichuris campanula
what is the pig whipworm?
Trichuris suis
what is the mouse whipworm?
Trichuris muris
what is the dog whipworm?
Trichuris vulpis
describe the body type of the adult Trichuris trichiura
Adult worm has a narrow anterior esophageal end and shorter and thicker posterior anus
how are male and female Trichuris worms differentiated?
- Females are larger than males; approximately 35-50mm long compared to 30-45mm
- males have a curled posterior
are eggs in feces embryonated for T. truchiura?
NO - they become embryonated in the soil before becoming infectious
where does the entire life cycle take place in T. trichiura?
in the human small intestine
give a description of the egg of T. truchiura?
- Eggs appear barrel-shaped
- unembryonated
- bipolar plugs
- smooth shell
what is the first intestinal stage after embryonated egg of T. trichiura?
- L1 larvae hatch in the small intestine
what is rectal prolapse?
the rectal area comes out of the anus if you have very high infection - Caused by the weakening of the ligaments and muscles that hold the rectum in place
describe the pathology of T. trichiura infection
- Most infections for humans are asymptomatic
- In some cases:
Heavy infection, especially in small children, can cause gastrointestinal problems (abdominal pain, diarrhea, rectal prolapse) and possibly growth retardation (stunting)
Malnutrition in children with heavy infection
how is T. trichiura infection treated?
Mebendazole is the drug of choice, with albendazole as an alternative
what is the treatment of T. trichiura (by mebendazole) effective against?
only the adult worm
never any of the larval stages or eggs
what stage does pinworm infect?
the egg stage
what is an inherited parasite?
it is a host‐specific parasite that has a long history of co‐ evolution with ancient human ancestors dating back to Africa before human dispersion across the continents.
what is a synonym for pinworm?
Enterobius vermicularis
Seatworm
what age is common to catch pinworm?
school-aged children
what is the ONLY natural host of pinworm?
humans
what is a reservoir host?
parasite can complete its life cycle but not the host of choice
what is the morphology of the adult worms of Enterobius vermicularis?
- The worms are small, white, and threadlike (females 8‐13 mm x 0.3‐0.5 mm and males 2‐5 mm x 0.1‐0.2 mm).
- Females have a long, pin‐shaped posterior end from which the parasite’s name is derived
where in the GI tract do pinworms dwell?
primarily in the cecum of the large intestine, from where the gravid females migrate at night to lay up to 15,000 eggs.
describe the morphology of pinworm eggs
Pinworm eggs are flattened assymetrically on one side, ovoid, 55µm x 25µm in size, and embryonate in four to six hours
how many molts do E. vermicularis undergo?
4
where do the adult worms mature?
in the cecum before copulating to complete the cycle (6 weeks)
where does the entire life cycle of E. vermicularis occur?
The entire life cycle – from egg to adult – takes place in the human GI tract
what is the pathology of infection of E. vermicularis?
- The majority of infections with this nematode are asymptomatic.
- In some cases, the emerging females and the sticky masses of eggs that they lay may causes irritation of the perianal region, which in some cases may be severe.
- As the females emerge at night this may give rise to sleep disturbances, and scratching of the affected perianal area transfers eggs to the fingers and under the finger nails, which aids the transmission of the eggs, both back to the original host (autoinfection), and to other hosts.
- Depending on how much sticky mass – you can get irritated and possibly get a secondary infection
how are E. vermicularis diagnosed?
Tape test
what does mebendazole target in E. vermicularis?
the adult worms ONLY
the curly tail if for which sex?
male
what is the most common intestinal nematode of humans?
Ascaris lumbricoides
what is the largest intestinal nematode of humans?
Ascaris lumbricoides
what is the disease caused by Ascaris lumbricoides?
ascariasis
why are children more likely to be infected?
because the eggs are found in soil and children play in dirt
who is the only DH of A. lumbricoides?
humans
why is A. lumbricoides male tail curles?
the presence of spicules
what is seen at the anterior end of the adult worm A. lumbricoides?
three lips - the margin of each lip is lined with minuscule teeth
are the eggs of A. lumbricoides embryonated in the feces?
NO - they embryonate in the soil
what is the infectious stage of A. lumbricoides?
eggs
do A. lumbricoides have a thick or thin shell?
thick
what is the path taken by A. lumbricoides in the host?
- The L1 larvae hatch, burrow through the intestine, reach the lungs, and finally migrate up the respiratory tract.
- From there they are then re‐swallowed and mature into the adult worm in the intestine.
describe the life cycle of A. lumbricoides
- Adult worms live in the lumen of the small intestine. Eggs are passed with the feces. Unfertilized eggs may be ingested but are not infective.
- Fertile eggs embryonate and become infective after 18 days to several weeks, depending on the environmental conditions (optimum: moist, warm, shaded soil).
- After infective eggs are swallowed, the L1 larvae hatch, invade the intestinal mucosa, and are carried via the portal, then systemic circulation to the lungs.
- The larvae (L3) mature further in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed. Upon reaching the small intestine, they develop into adult worms.
- Between 2 and 3 months are required from ingestion of the infective eggs to oviposition by the adult female.
- Adult worms can live 1 to 2 years.
describe the pathology of infection of A. lumbricoides in the lungs
- L3 Larvae cause problems in the lungs when they break through the lung capillaries to enter the respiratory tree.
1) small hemorrhages are produced causing plasma to enter alveoli
2) inflammatory response to this damage occurs resulting in pneumonia‐like symptoms. The symptoms of the pneumonia are low fever, cough, blood‐tinged sputum, asthma. - The more eggs ingested, the more migrating larvae and the greater the patholog
describe the pathology of infection of A. lumbricoides in the intestine
- The presence of a few adult worms in the lumen of the small intestine usually produces no symptoms, but may give rise to vague abdominal pains or intermittent colic, especially in
- children. A heavy worm burden can result in malnutrition.
- Wandering adults may block the appendicle lumen or the common bile duct and even perforate the intestinal wall. Thus complications of ascariasis, such as intestinal obstruction, appendicitis, biliary ascariasis, perforation of the intestine, pancreatitis, etc., may occur.
How is A. lumbricoides diagnosed?
eggs in feces - the eggs have a thick, rough outer shell
no way to diagnose with micgrating larvae
what is the treatment of A. lumbricoides?
- The drugs of choice for treatment of ascariasis are albendazole with mebendazole, and ivermectin as alternatives (all target the adult worm)
- no treatment against migrating larvae
what is the racoon roundworm?
Baylisascaris procyonis
where is Baylisascaris procyonis common?
NA
what are the infection rates of Baylisascaris procyonis?
as high as 70% in adult raccoons and exceeding 90% in juvenile raccoons
how are humans infected with Baylisascaris procyonis?
accidental ingestion of the eggs from the environment
what happens to humans when they are infected with Baylisascaris procyonis?
- Migration of the larvae through a wide variety of tissues (liver, heart, lungs, brain, eyes) results in visceral larva migrans (VLM), neural larval migrans (NLM) or ocular larva migrans (OLM) syndromes.
- Baylisascaris larvae continue to grow during their time in the human host.
- Tissue damage and the signs and symptoms of baylisascariasis are often severe because of the size of Baylisascaris larvae, their tendency to wander widely, and the fact that they do not readily die.
how is racoon roundworm diagnosed in humans?
serology, or by identifying larvae in biopsy or autopsy specimens - often not diagnosed initially due to lack of consistent diagnostic methods
what is the treatment for racoon roundworm?
no drugs have been demonstrated to be totally effective for the treatment of baylisascariasis
why are there no effective treatments for baylisascariasis?
the drugs only are effective against adult worms - NOT the eggs or larval stages
what are the different kinds of larval migrans of Baylisascaris procyonis?
- visceral larva migrans (VLM)
- neural larva migrans (NLM)
- occular larva migrans (OLM)
