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75 Cards in this Set
- Front
- Back
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Do parasites kill their hosts?
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NO
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What is a major difference between protozoa and helminths?
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Protozoa multiply within their hosts. The expression of disease is dependent on the parasite virulence factors and the host defense.
Helminths do not multiply within their hosts. The severity of disease depends on the parasite burden and immunologic response to parasites. It is more dependent on the number of individual events in which a person acquires the parasites. Expatriate infections and native infections (constant exposure to parasite) present differently. |
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What are the forms helminth can take?
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They begin as eggs that can become larva or cysts. As larva if they are presented with the correct environment they will become male and female adults. Some worms become male and female worms such as tapeworms (each section of the worm is either a male or female). If the eggs become cyst, which grow inside of tissue, they form a germinal membrane that sprouts the head of an adult worm. This cyst can then become an adult worm if put in the right conditions.
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What are the 3 ways helminth's can enter humans?
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Ingestion of eggs or tissue cysts
Arthropod bites transmitting larvae Penetration of intact skin or the mucous membranes by the larvae |
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Once inside a human, what is necessary for parasites to do to complete their life cycle?
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They must migrate to the correct location within the host. Non-human parasites that infect humans are unable to do this since they lack those human-specific signals telling them where to go. These parasites result in dead-end infections in humans and end up dying and not propagating (the infection causes different manifestations that what might be expected). These parasites can haphazardly travel throughout the body going through viscera and resulting in huge inflammatory responses but they eventually go away.
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What is an example of the symptoms from an animal parasite that infected a human?
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The animal hookworm that infects the human skin causes cuteanous larvae migrans in which the larvae just migrates within the superficial skin because it is unable to get to to the blood to complete its life cycle. This larvae will eventually die off in 2-3 weeks and thus is a self-limiting disease.
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What are the consequences of and responses of hosts to parasite infection?
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It is rare for a hemolinth infection to cause direct tissue damage
Hypersensitivity reactions of the host to the parasite are COMMON and causes the majority of the symptoms seen with these infections Eosinophilia is also a common response that occurs with helminth infections (NOT protozoa infections). It occurs due to the migration of the helminths throughout the tissue (thus is doesn't occur with helminths that stay in one location inside the body). It is induced due to the presence of objects too large for PMNs to consume. The eosinophils do not try to ingest the objects by line up and degranulate against it. |
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What are the 2 classifications of helminths and what are the subclasses within them?
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Nematodes (roundworms)
Platyhelminthes (flatworms) - Trematodes- flukes; they do not move much and are flat and sessile - Cestodes- tapeworms; they are segmented and each worm is essentially a colony of worms; each segment of the worm is an individual worm with the germinal center at the head of the worm |
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What are 6 common helminths that cause intestinal disease?
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Strongyloides- it is able to complete its life-cycle prior to leaving the host; it has an autoinfection cycle; it is a roundworm
Trichiuris- roundworm Enterobius- pinworm; roundworm Ascaris- roundworm Strongyloides- roundworm Hookworm- roundworm |
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What are the 5 common helminths that cause invasive diseases?
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Trichinosis- roundworm; causes muscle pain; transmitted by consumption of uncooked meat
Filaria- roundworm; the worms are found in the lymphatics or under the skin Schistosomiasis- fluke; the worms are found in the liver or urinary tract and cause granulomas and fibrosis Cysticercosis- tapeworm; the worms cause cysts in the brain that can result in seizures Echinococcus- tapework; the worm causes massive cysts in the liver or lung |
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What is the life-cycle of the nematodes (roundworms) Trichiuris and Enterobius (pinworm)?
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An individual is infected with adult nematodes in their infection. The eggs of the nematode are excreted into the soil via feces. The eggs then can be ingested by an unsuspecting human (fecal-oral transmission). Upon ingestion the eggs hatch and become adult worms in the intestine of the human again.
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What is the life-cycle of the nematode (roundworm) ascaris?
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An individual is infected with adult nematodes in their infection. The eggs of the nematode are excreted into the soil via feces. The eggs then can be ingested by an unsuspecting human (fecal-oral transmission). Upon ingestion the eggs turn into larvae that enter the bloodstream. In the blood stream the larvae go up the lungs and pass through it. They then migrate upwards and are swallowed resulting in infection of the human in the intestine.
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What is the life-cycle of the nematodes (roundworms) Strongyloides and Hookworm?
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An individual is infected with adult nematodes in their infection. The eggs of the nematode are excreted into the soil via feces. Larvae hatch from these eggs within the soil. The larvae penetrates intact skin exposed to this soil. It enters into the blood stream and makes its way to the lungs. They pass through the lungs and then migrate upwards and are swallowed resulting in infection of the human in the intestine.
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What are some common symptoms associated with ascaris infection of the intestines in healthy hosts?
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Diarrhea is NOT common
Possibly cramping or indigestion Obstruction of the intestine is common This is a BIG parasite. |
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What are some common symptoms associated with hookworm infection of the intestines in healthy hosts?
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Anemia- these worms are able to latch onto the intestinal wall and feed on RBCs; they bury into the outer mucosa and consumes blood.
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What are some common symptoms associated with pinworm infection of the intestines in healthy hosts?
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Anal itching; this is how pinworm is transmitted too
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Which intestinal nematodes can cause Loeffler's pneumonia as a result of infection and what part of the life-cycle is this associated with?
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Ascaris
Strongyloides Hookworm This is associated with the larvae passing through the lungs via the blood. It can result in a cough or asthma-like symptoms. There is a stage of larva development that occurs in the lungs. |
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Which intestinal nematodes can cause rash as a result of infection and what part of the life-cycle is this associated with?
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Strongyloides
Hookworm This is associated with the larvae penetrating through the intact skin to initially infect the host. |
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What is one way to identify pinworm eggs on a child's butt?
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Use scotch tape and peel it off and you will see the eggs.
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What time do the female pinworms lay their eggs and thus when you are most likely to see it?
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NIGHT
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What happens if a child is infected with ascaris and spikes a temperature?
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These parasites do not like high temperatures so they will try to get out of the body.
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What is the life-cycle of the Strongyloides worm?
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You have adult worms in the intestine (they can live there for about 6 months-1 year). They result in the production of eggs. These eggs hatch in the intestine into Rhabtidiform larvae. These larvae then are either excreted into the soil or remain in the intestine. They molt twice to form filariform larvae. These filariform larvae, if in the soil, can penetrate through intact skin and get into the bloodstream. If the filariform larvae are still in the intestine they can re-penetrate through the intestine and get into the blood stream, starting the cycle over again within that individual (AUTOINFECTION). Once the larvae are in the bloodstream they are able to pass through the lungs, get swallowed and end up back in the intestine re-starting the cycle.
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What is unique about the strongyloides life-cycle and do you have to treat it?
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The Strongyloides life cycle can be completed in the host. It MUST be treated. You can carry this parasite asymptomatically for DECADES due to this autoinfection.
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What happens if an individual with a Strongyloides infection becomes immunosuppressed?
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They have a much higher level of recycling of the parasites (hyperinfection) and resulting manifestations of disease at various parts of the life-cycle.
-Larva currens: a rash around the anus can occur where the larvae penetrate through the end of the colon to re-enter the bloodstream - Recurrent gram negative bacteremia and meningitis can occur when the larvae is present in the blood -Loeffler's pneumonia (looks like asthma) or broncospasms can occur when the larvae pass through the lungs. - GI distress and diarrhea can occur with the adult worms in the intestine. |
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What worm causes Trichonosis and what are some common clinical manifestations at 2-4 weeks after exposure and 4-8 weeks after exposure?
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Trichonosis is caused by Trichinella spiralis.
2-4 weeks after exposure: -Severe myaliga and weakness (masseter, extraocular and neck muscles) -Muscle tenderness - Fever +/- chills - Facial or periorbital edema - Conjunctival and nail hemorrhages - eosinophilia - Increased muscle enzymes 4-8 weeks after exposure: - Neurologic and cardiac symptoms - Mortality of 2% Most people get better by themselves after being very sick. |
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What is the life-cycle of Trichinella spiralis (helminth roundworm)?
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This pathogen is passed on via a cycle of carnivorism among hogs and rats. Humans ingest the cysts in infected, undercooked pork. the cysts become larvae in the stomach and burrow into the small intestinal mucosa. They can re-emerge as adult males and females and produce larvae which are capable of penetrating the intestine and circulating in the blood stream. These larvae then enter skeletal muscle cells and become cysts that remain in the muscle. Eventually these cysts will die and this is what causes all of the muscle pain associated with this infection (humans are dead end hosts).
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How do you diagnose Trichonosis?
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Muscle biopsy
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What is the major product associated with Trichinosis?
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Pork products! Other meat products can also pass along this parasite but it is less common.
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How do you treat trichinosis?
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Antihelminthic (Albendazole) is used to kill any adult worms within the intestine. This stops the production of larvae.
Steroids can be given to relieve the inflammatory reactions occuring. Antipyretics can be used to reduce any fever that might be present. NOTHING can be done about he larvae that have already formed cysts in the muscle. The pain from these cysts will take about 2-3 weeks to go away. |
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How do you prevent Trichinosis?
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Feed only SPECIFIC SANITIZED food to pigs
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What is the life-cycle of the lymph-dwelling Filaria?
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Filaria is transmitted to humans via a mosquito vector that deposits the pathogen into the blood. The parasite travels to and lives as adult worms within the peripheral lymphatics. they form a coil of male and female parasites in the lymph nodes. This mating generates eggs which hatch into larvae within the females body. The larvae (microfilariae) circulate in the bloodstream.
An example of Filaria that causes this is Wuchereria bancroftii. The main feature of this disease is lymphatic obstruction. The larvae are produced by the females and circulate in the blood during the middle of the night. |
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What is a long-term consequences associated with persistent lymph-dwelling Filarial infection?
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Elephantiasis- all of the lymph channels and drainage can be blocked by the parasite resulting in chronic lymphedema.
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What is the life-cycle of the skin-dwelling Filaria?
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The vector for these pathogens are biting flies such as the horse fly. The adult worm pairs result in skin nodules or are migratory. They generate larvae (known as microfilariae) that migrate through the dermis. The form of filaria that forms skin nodules is Onchocerca volvulus and the form of filaria that is solely migratory is loa loa.
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What is Onchoocerciasis?
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This is also known as river blindness and is caused by the Hemolinth Onchocerca volvulus. Its habitat is the bushes and vegetation around rivers and bodies of water in tropical places. The O. volvulus microfilaria can be found in skin snips and are located superficially in the skin. They result in depigmentation of the skin due to chronic microfilarial production, degradation, and a resulting allergic host response in the skin. (leopard skin). These microfilaria migrate in the skin until they die. The nodules generated are very itchy. The nodules contain male and female adult worms that are the source of the migrating microfilariae. The dreaded complication associated with this infection is the hemolinth migrating into the eye and causing the anterior chanper of the eye to become opaque causing the river blindness.
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What are some of the symptoms seen with Loa Loa infection?
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Loa loa infection can cause swellings that are itchy, painful and restrict motion. These swellings last about a week and come and go all over the body. This organism can also get into the eye and cross the conjunctiva causing problems. The way to treat it is by leaving it alone and doing nothing.
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What is Dirofilaria?
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This is a Filaria nematode (roundworm). It is also known as the dog heart worm. It can cause nodules in the lungs that are composed of dead and calcified tissue (which can be mistaken for cancer). Humans are a dead-end host for this worm.
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What is the role of Wohlbachia in filiaria infections and what is Wohlbachia?
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Wohlbachia is a rickettsia-like organism that has an endosymbiosis with Filaria worms. They are required for the worms to effectively replicated and for their long-term viability. These organisms infect the Filaria and live within them. Their LPS is though to be the cause of the inflammatory response seen with parasite infections.
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How do you treat a filaria infection?
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You must treat to kill both the worm and the microfiliaria. The microfilaria can be killed by ivermectin (an anti-helmithic drug). The adult worms are killed via Tetracycline which kills the embosymbiont and thus leads to the death of the adult worms.
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What is the new diagnostic test available for Onchocerciasis?
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You can look for NATOG levels in the urine. This is the breakdown product of a neurotransmitter specific to the parasite. It is at the highest levels in viable adult worms and levels decrease upon treatment of the patient with tetracycline.
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What drug are ALL intestinal nematodes susceptible to?
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Abenazole; Trichinosis is also susceptible to this drug
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What is an example of the main result of a lymphatic Filaria infection and the host response to it?
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Lymphatic infections- you get blockage of the lymphatics by the adult worms
Microfilaria die and result in the inflammatory response where you see symptoms in the patient. They result in a Type 1 hypersensitivity reactions in the host. |
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Which helmithic disease is the worst and where can you find it geographically?
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Schistosomiasis
It is found mainly in S. E. Asia and Africa. |
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What is the structure of the larvae associated with Schistosomiasis?
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The larvae form is the form in which the Schistomia penetrates the skin and gets into the blood stream. It contain a head that holds all the genetic material and results in the penetration of the skin and a tail that is just used for swimming.
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What is the life-cycle of the human form of Schistosomiasis?
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An infected individual releases the parasite eggs into fresh water via their feces or urine. The eggs hatch to form larvae. These larvae (merosidium larvae) infect snails in the water. The snails are an intermediate host and while inside the snail the merosidium larvae develop into CERCARIA larvae which are then released from the snails. The CERCARIA larvae (the skin penetrating form of the larvae) infect humans that come in contact with the infected water source via penetration through the skin.
There are different species of Schistosomia that causes Schistomiasis. Each species also ONLY infects a specific species of snail. |
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What happens once the Schistosomia parasites penetrate human skin?
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Once the Cercarial larvae penetrates the skin its gets into cutaenous venules. Then it migrates up to the lungs where it has a period maturation in which it develops as a schistosomulae. In this stage it may trigger a self-limited febrile illness due tot he organism inducing enough antibodies to generate antibody-antigen complexes that lead to fever (this is rare). The male and female schistosomulae then migrates into the venous plexus into the abdominal venules. Different species of Schistosomia migrate to different plexi. At these locations the male and female worms mate and produce eggs (the females have a groove in their body that captures male worms; this generates a CONSTANT site of copulation and egg production). The eggs get into the circulation (portal circulation) and can migrate out of the body through visceral organs (such as through the feces) or become trapped and die in tissues (such as in the liver).
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To what abdominal venules do the Schistosomia species migrate?
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S. japonicum migrates to the Superior mesenteric venous plexus (the small intestine venous plexus) and thus the eggs from this species are released via the feces.
S. mansoni migrates to the Inferior mesenteric venous plexus (the venous plexus that drains to the portal system from the colon) and thus the eggs from this species come out in the feces as well. S. hematobium migrates to the bladder venous plexus and thus the eggs from this species come out in the urine. |
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What causes the pathology seen with Schistosomiasis?
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The pathology is caused by the CONSTANT production of the parasite eggs. These eggs get trapped in tissues and die. This induces a type IV hypersensitivity reaction that leads to granuloma, tissue scarring and resulting organ damage.
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What is a distinguishing feature between the different forms of Schistosomia eggs?
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The location and presence of a spine.
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Does Schistosomiasis occur in the U.S?
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YES! We have it in Michigan. It is caused by birds pooping in water.
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Can the immune system mount a response against the adult Schistosomia parasites?
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NO, the adult male and female worms are invisible to the immune system via their ability to coat themselves with host proteins. This makes them almost impossible to get rid of and they can live for up to 5-10 years. These worms also minimally express surface antigens assisting with this invisibility and survival.
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What are some presentations of Schistosomiasis?
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It can cause polyps and ulcers to form in the colon, scarring in the liver due to resolving granulomas from the eggs, and fibrosis of the portal tracts leading to obstructed portal blood flow (causes isolated portal hypertension).
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What is the pathogenesis of Schistosomiasis?
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Granulomas form around the eggs due to a Type IV reaction of the host. These granulomas eventually become fibrotic.
Morbidity of the disease depends on the worm/egg burden (the number of worms you are infected with and the amount of eggs being produced). |
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If you are infected with Schistosomiasis, can you get infected with more of this parasite?
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No, while you are infected with Schistosomia you have concomitant immunity to schistosomulae. This is mediated by IgE, eosinophils, and macrophages and allows the host to handle the burden of infection they currently have without getting more.
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What are the clinical presentations of Schistosomiasis?
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- Cercarial dermatitis- swimmer's itch
- Intestinal Schistosomiasis- granulomas form which can lead to polyps, protein loss, malabsorption, and strictures. - Hepatosplenic schistosomiasis- the result is portal hypertension which leads to ascites, varices (these can burst and cause the patient to bleed to death), splenomegaly , and hemorrhoids but the patient still has NORMAL liver function. - Urinary schistosomiasis- this can lead to hematuria (the indivdiual pees normal pee and then at the end of hte urine stream they pee blood), chronic infection (leading to strictures and scarring of the urinary tract), obstruction and cancer. - Other effects include cardiopulmonary (deposit of eggs in the lungs can lead to right heart failure) and CNS effects. |
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How do you treat Schistosomiasis?
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Praziquantel- this drug increases the permeability of the adult parasite to Ca+2 leading to Tetanospam and its death. A single dose cures 65-90% of individuals. It is VERY effective! For those individuals not cured, the egg excretion of the parasite decreases by 90%.
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What are 4 interventions that could be used to prevent Schistosomiasis?
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Reduce the carriers- mass treatment programs
Eliminate the intermediate snail hosts- molluscicides, destroy the snail habitats (snails need vegetation to survive), introduce snail eating fish Prevent H20 contamination- install latrines, toilets, public health education, etc... Prevent human exposure- use water systems to wash clothes and bath |
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What form of the parasite are in the definitive and intermediate hosts of tapeworms/cestodes?
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The definitive hosts harbor adult worms ONLY
The intermediate hosts harbor tissue cysts (which contain worm heads) |
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How do humans acquire infection by tapeworms?
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1) Ingestion of tape worm eggs from the feces of an infected animal or human (this leads to them acquiring tissue cysts making them intermediate hosts)
2) Ingestion of tissue cysts in undercooked meat (which leads to them acquiring an adult tapeworm making them the definitive host) |
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Are humans the intermediate or definitive hosts of tapeworms?
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BOTH
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What is Taeniasis?
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This is an infection cause by a tapeworm.
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What tapeworm results in Cystericercosis?
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The Pork Tapeworm
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What is the cycle that leads to both tapeworm and cystericercosis in humans?
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Humans infected with tapeworm will excrete the eggs in their feces. Due to poor hygiene they consume some of these eggs which turn into larvae and migrate to various tissues throughout the body to generate cysts. This results in CYSTICERCOSIS. Other humans can also consume the eggs via fecal contamination and get CYSTICERCOSIS.
The parasite eggs within the feces can be consumed by a pig (intermediate host). These eggs turn into tissue cysts within the pig. Then humans who consume infected undercooked pork will get TAPEWORM. |
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What does a cyst with a calcified dot on a CT represent?
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It represents a dead cyst containing a dead and calcified worm head (the dot).
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What can occur to the skin and muscles with Cysticercosis?
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The muscles can diet and calcify. Nodules can also form in the skin.
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What is the dreaded complication of Cysticercosis?
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Cysts in the brain. If you see a CT scan of a brain and you see holes in the brain this patient has Cysticercosis.
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What are the cysts called that form during Cystcercosis?
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Cysticerci; the all have germinal membrane with a SINGLE worm head inside of it
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What is Echinococcosis?
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This is a disease that is caused by a tapeworm. It is also known as Cystic Hyatid Disease.
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What are the cysts that form in Echinococcosis?
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Hydatid cysts. Only a SINGLE cyst forms per host but the cysts are made up of a germinal membrane that KEEPS producing worm heads and thus is full of 100s of worm heads.
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What is the cycle of Echinococcosis?
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A dog infected with the tapeworm secretes eggs in its feces. These eggs within the feces are ingested by humans from contact with the dog leading to Echinococcosis. Humans develop hydatid cysts within their liver (and some in their lungs and other organs). The feces containing the eggs can also be ingested by sheep grazing in pastures. The sheep develop hyatid cysts within their bodies. The sheep eventually die and the dogs will eat the dead, sheep infected with tapeworm cysts and get tapeworm. In this cycle sheep are intermediate hosts, humans are dead-end hosts and the dogs are the definitive hosts.
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What is found on the head of the tapeworms responsible for Echinococcosis?
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The heads of these worms are covered in hooklets that attach to the dogs intestine. You might see free teeth from the head of the worm in samples.
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What can happen to hyatid cysts in the human host?
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They can die and calcify and be asymptomatic for years.
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How do you treat BOTH Cysticercosis and Echinococcosis?
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Antihelminthic therapy including either Albendazole or Praziquantel.
Echinococcus sometimes requires the surgical removal of the cysts or irrigation-evacuation of the cysts. You should treat only those cysts that are not calcified. Cysticercosis requires that you give steroids at the same time as the antihelminthic drugs to decrease the inflammatory response of the host due to the cysts breaking up within the brain. These cysts cannot be surgically removed. |
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What are the determinants of the symptoms seen with Echinococcosis?
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Symptoms are related to the size of the hyatid cyst and the pressure it is putting on organs.
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Who are the definitive hosts, intermediate hosts and dead-end hosts in the life cycle of the Pork tapeworm?
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Definitive host (contains adult tapeworms)- humans
Intermediate host (contains tissue cysts)- pig Dead-end host- humans |
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Who are the definitive hosts, intermediate hosts and dead-end hosts in the life cycle of the Echinococcus tapeworm?
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Definitive host (contains adult tapeworms)- dogs
Intermediate host (contains tissue cysts)- sheep Dead-end host- humans |
