(From Dr. Adebiyi’s micro lecture, 15 Nov 2000, by Brian Buschman)
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Entamoeba histolytica is the only GI amoeba. It exists in two forms being a cyst that can survive outside the body and causes infections and in the form of a trophazoid body which is the form that actually infects people.
E. histolytica is recognizable by it’s small nucleus with the central karysome and chromatin around the nuclear membrane. When it infects the GI it causes “tear-drop” ulcers.
E. histolytica infections can be one of four types:
1) Asymptomatic
2) Symptomatic with simple infection.
3) Intestinal amebiases with various intestinal problems.
4) Extraintestinal amebiases that show focal legions all over the body. This type can be fatal.
Giardia is a cause of traveler’s diarrhea from an intestinal flagellate. It also exists in cysts for infection and trophozoites as an active form. You will get a nasty diarrhea that should clear up on it’s own (no drugs needed).
Balantidum is an intestinal ciliate that rarely infects humans. Of course you diagnose it in the feces given that it’s an intestinal parasite.
Isospora is an opportunistic infection seen with AIDS al over the world. It passes and is diagnosed by it’s oocytes through the stool. It undergoes both sxhizogony (asexual reproduction) and sporogony (sexual reproduction).
Cryptosporidium is an ACID-FAST zoonotic organism. It is most often seen in AIDS patients.
Trichomonas is an STD that lives in vaginas and urethras. It has no cystic form. Since it only lives as a trophozoites it only spreads by direct contact (SEX).
Naegleria (like Nagline bottles) is related to water so it infects people that are swimming or diving. It enters through the nasal mucosa and can cause PAME (primary amoebic meningoencephalitis).
Acanthamoeba is another one for AIDS patients. They get granulomastous skin disease and ulcerations of the cornea. Acanthamoeba shows up in the CSF.
There are three forms of Trypanosoma that present alphabetically from West to East.
Trypanosoma cruzi is the American variety which spreads fecally by the “kissing bug”. The flies carry it in their feces and they poop while they eat. If they poop on your skin and then bite you at the same spot they inject Trypanosoma into you.
It leads to ulcers and facial swelling. It grows in cells (specifically in the heart). Anything that grows intercellularly can be detected by a skin test. Since it is intracellular it also causes those cells to undergo hypertrophy while it grows and then lyses the cells to release itself.
Diagnosis is either by examination of tissue or blood but can also be done by xenodiagnosis which is when you let a “sterile” fly bite you and then biopsy the bug for the disease.
Trypanosoma gambiense is the West African variety that is carried by the Tse tse fly. It produces an intermitted fever ONLY in humans. It shows Winterbottom’s sign being lymphadenopathy near the site of the bite. Ultimately it invades the CNS and leads to death.
Trypanosoma rhodesience is the East African kind that is similar to T. gambiense.
There are three Leishmania that are all spread by the sandfly. Different species affect different tissues:
1) Dermal/cutaneous Leishmania.
2) Mucocutaneous Leishmania is an intracellular organism therefore it shows up on skin testing. It causes extensive tissue destruction.
3) Visceral Leishmania is the most severe Leishmania. It causes anemia.
The tissue Sporozoa includes Malaria, babesiosis, toxoplasmosis and pheumocystosis. They have a life cycle of schizogony in humans and sporogony in non-human hosts.
Malaria is caused by Plasmodium that exists at sporozoites in the mosquito, as it is injected into the human and as it enters the liver. In the hepatocytes, Plasmodium then changes to become merozoites that go to infect the RBCs. When the RBCs lyse they release a new batch of sporozoites.
It you want to attack it while it is being injected into humans then you need to prevent sporozoites. If you want to kill it after it’s already in the system you aim to attack merozoites.
The morphology involves junk from lysed RBCs clogging up the spleen causing hepatosplenomegaly. The lysed RBCs also stick to capillaries helping to block them. Either of these can lead to death. The lysed RBCs also loose all their “parts” leaving to high bilirubin levels that cause “black-water” urine.
Babesiosis is like malaria except that it is transmitted via a tick and humans are not the only vectors.
Toxoplasmosis is carried by cats that get it by eating infected mice. It is then spread to humans by inhalation of cat “stuff” or by the fecal-oral route often after gardening. It is especially bad in the immunocompromised and in the pregnant.
You need to know the following trematodes (flukes), where you find them in the human and where they come from.
|
Lung Flukes |
Paragonismus westermanii |
Snails and crabs |
|
Liver Flukes |
Fascuola hepatica |
Snail and vegetables |
|
|
Clonorchis sinensis |
Snail and fish |
|
Blood flukes |
Schistosoma |
Snails |
As a blood fluke Schistosoma may infect the intestinal tract (S. mansoni and S. japonicum) and S. haematobium will get the bladder.
Echinococcus granulosus causes hydrated cysts which are full of sand-like hydrated particles. If you try to biopsy or remove them be sure not to rupture them or you run the risk if:
1) Anaphylactic shock
2) Creating more cysts
Diphyllobothrium latum can grow to be up to 40 feet long and competes with the host for vitamin B12 in the gut. It therefore causes pernicious anemia.
Ascaris is one of the forms of worms that migrate all over the body and settle in the gut. It can live in the gut of adults but it easily blocks the GI system of a kid.
It any patient intestinal worms cause bloating even in the fasting state.
Strongyloides is a thread-worm that can produce fertile eggs without male help. It’s larvi cause the infection. If a person is immunocompromised they will get an increased worm load.
Enterobius is the worm most often seen in the US. It effects children mostly and is diagnosed by the “scotch-tape” test.
Both Necator americanus and Ancylostoma cause creeping larval migrans from the penetration of bare feet. In pregnant women it leads to stillbirth.
Trichuris trichiura does not travel the body. IT does cause rectal prolapse.
Trichinella spiralis migrates to the skeletal muscle where it forms cysts. Dr. Tweeddale wants us to know it causes:
1) Muscle pain
2) Periorbital edema
3) Eosinophilia
Brugia malavi
Both Wuchereria and Brugia causes elephantiasis and carried by mosquitoes. In both humans are the only natural host.
Wuchereria shows microfilariae that are nocturnal.
Onchocerca is a worm carried by the black fly. It causes dermatitis and BLINDNESS. With a skin section put in saline you can see the microfilariae.
Loa loa causes eye problems and releases microfilariae that are seen diurnally (in the afternoon).
Dracunculus medinensis is the only one spread by a CRUSTATION rather then by an insect. Dracula is like a man but is wired in how he feeds. Dracunculus is like all the other worms but spreads by crustations rather then the normal insect vector.
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