Parasites Flashcards
What are the two types of parasites and their distinguishing characteristics?
- Protozoa, unicellular (intracellular or extracellular)
2. Helminths (worms), up to meters long
What is African trypanosomiasis caused by?
Trypanosoma brucei - motile, vibrating parasites in the blood of livestock
Is trypanosomiasis a zoonosis?
Yes, from cows/horses
How is trypanosomiasis spread?
Tsetse fly transmission to humans causing “sleeping sickness”
What is the immune response to trypanosomes?
If parasites live extracellularly in the bloodstream, the infection is normally controlled by antibodies that eliminate the parasites.
If the parasite is able to escape the antibodies, it can spread to the brain and cause severe disease symptoms.
What is giardia?
Giardia infection is an intestinal infection marked by abdominal cramps, bloating, nausea and bouts of watery diarrhea. Giardia infection is caused by a microscopic parasite that is found worldwide, especially in areas with poor sanitation and unsafe water.
Tell me about the giardia parasite.
- Parasites attach to mucosal epithelium and can survive for weeks in the host.
- Prophozoite form is replicating form in intestine.
- Cyst form passed in feces.
What is the animal reservoir for giardia?
Beaver
What is toxoplasmosis?
Zoonosis caused by Toxoplasma gondii parasite commonly found in contaminated food or rat feces.
How is toxoplasmosis spread?
T. gondii forms cysts in muscle tissue and oocysts in fecal tissue. Oocysts in fecal tissue are ingested by mice or humans (smell) and form tissue cysts in muscle or nerve muscles. Ingesting undercooked meat from animals with cysts in tissue also spread the disease.
Tell me the prevalence in the United States, Canada, France, and Brazil.
US: 9-11%
Canada: 17%
France: 47%
Brazil: 50%
What is a definitive host?
Hosts in which the adult form matures. This is usually host where sexual reproduction takes place.
What is an intermediate host?
Those which may have larval forms or cysts form. For many parasites, the cyst form in the intermediate host must be eaten (and digested out of cyst) to pass onto a definitive host.
What is a dead-end host? What’s an example of one?
An intermediate host that does not allow transmission to a new definitive host. For example, a dead-end host could be tapeworm cysts in humans where the flesh is unlikely to be eaten by carnivores.
What is the definitive host, intermediate host, and dead of Toxoplasma gondii?
Intermediate: rat
Definitive: cat
Dead-end: human
What are is the most common infection worldwide?
Parasitic worms
Most worms do not cause great ___ but can result in ___ for infected individuals?
mortality, morbidity (disease effects)
Why does helminth size matter in terms of immune response?
The large size of helminths (large enough to be seen with the naked eye) makes it difficult to eliminate by normal immune function. Worms are often “ignored” by the immune system rather than causing disease in attempts to eliminate the worms.
Where can worms live?
- Most extracellular worms live in the intestine.
- Schistosoma worms are blood flukes that reside in blood vessels.
- Guinea worms live in peripheral tissues.
- Intestinal worms traffic through lungs or other tissues as part of life cycle.
- Worms can be found in intracellular cyst form (which enhances transmission).
What is the most common worm infection in the United States?
Nematode
What is pinworm?
An urban pathogen caused by the worm Enterobium vermicularis.
Prevalence of pinworm infection in children can be as high as __%.
50
Is there an animal reservoir for pinworm?
No
How are pinworms spread?
Small segmented roundworms transmitted through fecal/oral route. People are infected by ingesting eggs from fingers, clothing, and other surfaces.
Adult pinworms can achieve what length?
1 cm
What are the most common sites of outbreaks of pinworm?
Childcare centers
How can pinworm be diagnosed?
Itching and examining for eggs by tape test
What is ascaris?
Large round worms that live in humans’ small intenstines (although another species infects pigs!).
More than __ billion people are thought to be infected with ascaris at any given time.
1
Adult female ascaris can reach up to __ cm long, whereas males are ____.
30, smaller
Detail the ascaris lifecycle.
Ingested egg hatches in small intestine. → Larvae penetrate the intestine, travel through lymph and blood to liver, heart, and lungs. → Larvae mature in liver and then travel out capillaries into lungs where larvae are coughed up and swallowed to enter intestine (9 days after initial infection). → They mature over next 8-12 week into sexually mature adults.
Ascaris is highly endemic in many ___ and ___ areas where as many as __% of some communities will be passing Ascari eggs.
tropical, subtropical, 85
What is the primary preventive issue of Ascari?
Sanitary disposal of feces
The majority of infections are people with low ___ ___ and are usually ___.
worm burden, asymptomatic
Why are people with heavy worm burden still rarely diagnosed with Ascaris?
Because symptoms like stomach problems or pneumonitis are not specific to Ascaris
What does definitive diagnosis of Ascaris require?
Finding eggs in stool
What is the most life-threatening complication of Ascaris infection?
Blockage of intestine or bile ducts (with heavy worm burden)
Only in extreme cases do adult Ascaris worms…
exit the nose, mouth, or anus.
How is hookworm (a nematode) transmitted?
Contaminated feces or from contact with larval form in soil
What do hookworms ingest for nutrition?
Red blood cells
Hookworms hook onto ___ ___ with their “teeth.”
intestinal wall
Describe the hookworm lifecycle.
Larval form in soil enter through unbroken skin → Travel to intestine to mature into an adults → Find mate and produce eggs to pass in feces
Is trinchinella intracellular or extracellular?
Intracellular
Trichinella causes what and how?
Trinchinosis, by making cysts in muscle which can be transmitted to humans when they eat undercooked pork
Where to Trichinella live?
Intestine
How long are adult Trichinella?
1-2 mm
Detail the trichinella life cycle.
Ingestion of meat scraps or animal scraps by a pig → Ingestion of undercooked pork by a human → Larva released in small intestine → Larvae grow into adults → Larva deposited in mucosa → Encysted larva in striated muscle
What is Filariasis?
A parasitic disease caused by an infection with roundworms of the Filarioidea type.
For filarial worms, humans are what kind of host?
Definitive
Are filarial worms a zoonosis?
No, it has a mosquito vector
Detail the filarial worm lifecycle.
Mosquito takes blood meal and larvae enter skin → Worms become adults → Adults produce sheathed microfilariae that migrate into lymph and blood channels → Mosquito takes a blood meal and ingests microfilariae → Microfilariae shed sheaths, penetrate mosquito’s midgut and migrate to thoracic muscles → L1 larvae → L3 larvae → Migrate to head and mosquito’s proboscis where mosquito can then allow larvae to enter skin
What do filarial worms cause?
Lymphatic filariasis, or elephantiasis
Filarial worms are high on list of ___ ___ ___.
neglected tropical diseases
How many are estimated to be infected by filarial worms?
120 million
The Carter Center has provided targeted elimination with what? (2)
- Drugs donated by Merck and GlaxoSmith Kline
2. Insect treated bednets
What is another word for “guinea worm”?
Dracunculiasis
What causes guinea worm?
Ingestion of drinking water with infected small crustaceans (copepods)
Female Guinea worm forms painful lesions up to __ year after infection.
1
When exposed to water, the female releases ___ into water.
larvae
Guinea worm extends its ___ through the skin.
Anterior end
How do you remove guinea worm?
Gradual twisting
What is the key to limit transmission of guinea worm?
Education
Is there a vaccine or drug treatment to prevent guinea worm?
No
What are cestodes?
Flat segmented worms, primarily intestinal dweeling tapeworms
Why are cestodes true parasites?
They lack a mouth, alimentary tract, circulatory system, body cavity, and major metabolic pathways. These worms absorb their nutrient molecules through their body surface.
Tell me about tapeworm anatomy. (3)
- The scolex is the anterior-most portion of the adult worm and is armed with large hooks that alternate with small ones.
- The base of the scolex forms a neck which contains germinal cells that give rise to proceeding segments.
- The neck is followed by a chain of flat, ribbon-like segments referred to as the proglottids.
What do tapeworm infections cause?
Taeniasis
What are the harmful effects of taeniasis?
Cysts in muscle or liver may lead to muscle aches or inflammation; cysts in the eye might lead to blindness; cysts in teh brain may lead to neurological damage
What are trematodes?
Commonly known as flukes
What is schistosome? How long do they live?
A trematode blood fluke. These worms can be extremely long-lived in hosts, usually 4 years but can live up to 20.
How many people worldwide does schistosomiasis affect?
Over 200 million people
Schistosomiasis is endemic to __ developing countries throughout the tropics.
76
Detail the schistosome life cycle.
Eggs are released in urine or stool of infected individuals into fresh water where they hatch and infect the intermediate host, a freshwater snail. → After infection, asexual proliferation occurs in snail and thousands of new larval parasites (cercariae) emerge to swim and ultimately penetrate skin.
How is the schistosome couple configured?
The female worm is inside of the canal of the male worm
