Protozoal Infections
Gastrointestinal
Amebiasis: produced by Entameba histolytica and causes diarrhea in some
people, even weeks later (travelers) and rarely invades to produce abscesses in
distant organs (liver) after colonic lesions are gone Giardiasis: produced in traveler's by Giardia lamblia causes
malabsorption and diarrhea from inflammation of small intestine Cryptosporidiosis: produced in AIDS patients by Cryptosporidium parvum to cause
(usually) mild inflammation of small intestine with diarrhea Microsporidiosis: similar clinically to cryptosporidiosis; a number of organisms, such as Enterocytozoon bienusii, cause this condition. Isosporiasis: caused by Isospora belli and similar clinically to cryptosporidiosis; not common.
Pulmonary: Pneumocystis jirovecii (formerly P. carinii) causes a florid pneumonia in immunocompromised patients. Technically, Pneumocystis is a fungus, but morphologically resembles and clinically acts like a protozoan.
Bloodstream
Malaria
African trypanosomiasis
Parenchymal organs and tissues
Chagas disease: heart failure in 10% Leishmaniasis: kala-azar from L. donovoni produces hepatosplenomegaly and
lymphadenopathy; cutaneous leishmaniasis can be localized (oriental sore) or
mucocutaneous Toxoplasmosis: from Toxoplasma gondii, can be a congenital infection or a
CNS infection in AIDS. Pseudocysts form in tissues and contain bradyzoites. When the pseudocyst ruptures, the bradyzoites are released and become tachyzoites that can infect other tissues or be ingested.
HELMINTHIC INFECTIONS
GI tract worms
Ascaris lumbricoides: a big worm but little serious disease (rarely causes intestinal obstruction, appendicitis) Trichuris trichiuria: whipworm in colon can cause diarrhea Enterobius vermicularis: pinworm infection is relatively common and causes anal pruritis
Tapeworms:
Taenia solium (pork) and Taenia saginata (beef): cysticercosis results when the eggs of T. solium are ingested and cysts can develop in soft tissues (brain is worst) Echinococcus: ingestion of eggs causes hydatid disease in liver, lungs, bone
Necator, Ancylostoma: hookworm in small intestine causes blood loss and
anemia Strongyloides stercoralis: causes small intestinal inflammation with
malabsorption Flukes: many produce liver and biliary tract disease that can mimic
lithiasis and hepatitis; Paragonimus involves the lung
Bloodstream worms
Schistomomiasis: produces eggs that cause cirrhosis of the liver (S.
mansoni and S. japonicum) and cystitis, bladder cancer (S. hematobium). The eggs of Schistosoma species are seen here for comparison. The 90 micron egg of S. japonicum has no visible spine, only a terminal knob. The 150 micron egg of S. hematobium has a terminal spine, while the egg of S. mansoni, though of similar size, has a lateral spine.
Filariasis: lymphatics often involved in chronic infection Trichinosis: skeletal muscle involved
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