Microbiology 2500A/B Parasitology Summary.docx

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Microbiology and Immunology
Microbiology and Immunology 2500A/B
John Mc Cormick

Parasitology I Four groups: ectoparasites: spiders, insects, maggots; enteric protozoa; blood and tissue protozoa; Helminths: worms Enteric Protozoa  Associated with travel → longer incubation period than bacteria and viruses  The presence of any protozoa (even nonpathogenic varieties) in stool indicates exposure to contaminated food or water  Cysts are the infective form (very small). Trophozoites are the active form  protozoa are not normal flora; but some can be non pathogenic  traveler’s diarrhea → most likely bacterial than parasitic (protozoal or helminth)  Stools for ova & parasites (+ cysts): Examination of permanent stained smear is best method of diagnosis for enteric protozoa. 3 negatives stools before you can confidently rule out pathogens. 1) Giardia intestinalis (lamblia) – beaver fever  Most common cause of travel associated diarrhea  Acquired by contaminated water; waste of humans or waste of animals (beaver)  Noninvasive, resistant to chlorination (in water purification), must be filtered out via sand, iodination is a more active halogen, more effective at removing giardia from water  Soft foul stools w/flatus (foul farts), bloating, gurgling, weight loss, fatigue, obstipation (no passing gas)  Residual lactose intolerance common in Caucasians 2) Entamoeba histolytica Dispar is non-pathogenic  Non-specific symptoms: nondysenteric (alternating constipation/diarrhea, lower abdominal cramps, bloating, flatus (not foul smelling) and fatigue) to dysentery (cramps, fever, production of bloody stool)  Colon ulceration may lead to systemic spread via bloodsteam to liver, lungs, brain  Amebic serology is usually +ve w/invasive disease: there’re antibodies in blood when disease is invasive  Don’t usually see the trophozoite in stool samples (too big), normally it is only the cysts that we see  Trophozoite is the only amoeba that digests RBCs  Amebiasis: refers to infection caused by the amoeba Entamoeba histolytica o Amebic liver: right lobe abscesses respond to drug therapy o Left lobe abscesses need drainage as they tend to extend to the pericardium 3) Dientamoeba fragilis  Amoeba-like noninvasive flagellate. No cyst form (fragilis = fragile)  May be transmitted on pinworm (Enterobius vermicularis) eggs. Diarrhea, bloating, flatus, fatigue 4) Cryptosporidium parvum & hominis  Only 10 oocysts (acid fast stain shows them in stool) needed for infection (very infectious!), short incubation, hard to deal w/in AIDs  Water contaminated with farm run-off (found in animals), swimming pools 5) Cyclospora cayetanensis  Prolonged symptoms: watery diarrhea, indigestion, cramps, weight loss, marked fatigue  Associated with imported fruits  See oocysts with acid fast stain Blood & Tissue Protozoa Names host where sexual reproduction is called the definitive host (mosquito). The human is called the accidental host 1) Plasmodium species: causes malaria  Transmitted by anopheles mosquitoes, strict night biters. Stylet into capillary, regurgitate saliva (contains sporozoite)  Injects sporozoite → liver → schizont ruptures → merozoites parasitize RBCs → trophozoite → schizont → releases merozoites (asexual reproduction). Some merozoites → gametocytes (sexual reproduction)  Falciparum: parasitizes all stages of RBCs in the bone marrow  Vivax: infected cell larger b/c attacks young RBCs, not immediately deadly Malaria: serious → thrombocytopenia (low platelet), Giemsa stain, PCR is good to diagnose 2) Toxoplasma gondii  Most human infections are benign, asymptomatic, occasionally myocarditis  Intra-uterine neonatal infections: encephalitis, hydrocephalus, microcephaly (cerebral cortex undeveloped)  In immunosuppressed hosts: retinochoroiditis (blindness)  Raw meat ingestion  Definitive host: cat (gets it by hunting). Ova in cat feces take time to embryonate and become infectious. Clean litter box often  Bradyzoite: quiescent cysts. Tachyzoite: active form doing the damage.  Diagnosis of toxoplasmosis: serology or tissue biopsy 3) Leishmania  Cutaneous (topica) – Baghdad sore, mucocutaneous (braziliensis), visceral (donovani) kala azar  Transmitted by sand flies  Mucocutaneous Leishmaniasis: chiclero ulcer, espundia, o 3 stages: cutaneous (chiclero ulcer on ear), cicatrical (scars), mucocutaneous (late stage espundia – nasal septum deteriorates) o Diagnosis: biopsy lesions, Giemsa stain, spleen aspirate (risky), PCR, serology useless, Montenegro skin test  Cutaneous leishmaniasis: biopsy at edge of active lesion  Kala azar: L. donovani → enlarged spleen and liver 4) Trypanosoma → trypanosomiasis  T. Cruzi (south American – Chagas disease) o 3 C’s: C-shaped organism, cruzi is the species and chagas is the disease o Transmitted by kissing bug biting you around eye, rub feces (where organisms are) into eye o Chagas → Acute Phase: Organism may be found as motile trypanosomes in anticoagulated blood or in Giemsa stained thick & thin blood films. Find them in the blood. o Chagas → Chronic Phase: Xenodiagnosis and blood culture via animal inoculation  Let an uninfected kissing bug bite you, dissect them & look through microscope  T. Brucei (African, sleeping sickness → coma): not C shaped, more squiggly o Transmitted by tsetse fly (meat cleaver wing) o Winterbottom’s sign is the first stage of systemic disease, lymph nodes behind ear swollen , 5) Free living ameboe: naeglaria fowleri & acanthamoeba  Found in warm fresh water lakes, cause fatal CNS infections  Fowleri cause primary amebic meningoencephalitis  Acanthamoeba: cause granulomatous amebic encephalitis in immunocompromised Parasitology II: Helminths Tropical diseases caused by helminths: high prevalence, rural poverty, ancient, chronic disfigurement, low mortality A) Nematodes (roundworms): round cross section Intestinal nematodes 1) Enterobius vermicularis (pinworm)  Gives itchy butt (pruitis ani). They enter through stomach then lay their eggs on the perianal skin  Benign. Children scratch, eggs under nails, until they autoinnoculate Transmitted through contaminated soils 2) Ascariasis lumbricoides  Size of pencil. Worms both male (migrate) and female (lay eggs not infective until 2-3 weeks in soil)  Adult worms live in the upper small intestine  Problems arise due to migration of adult worms and hypersensitivity to larvae in lungs  After you ingest embroyonated eggs from soil contamination of food and water, there’s a pulmonary phase that goes through the lungs where you get blood tinged sputum, wheezing, cough, breathlessness  Eosinophils (WBCs) are associated with the clean-up of allergic reactions (allergies ↑ blood eosinophils)  Intestinal phase: Usually asymptomatic unless heavy infestation, adult worms may be coughed up, vomited or emerge from nose or anus. Adult worms may migrate into ducts & cause obstruction 3) Trichuris trichiura (whipworm)  Not very invasive; only massive infestations will cause diarrhea and bloody stool  Rectal prolapse: rectum turning inside out, not painful  Trichuriasis: light infections asymptomatic. Heavy infections → dysentery and blood loss in the stool o Trichuris dysentery syndrome → anemia, rectal prolapse, finger clubbing (finger nail bubbles up) and growth stunting 4) Intestinal hookworms: ancylostoma duodenale & necator americanus  Suck blood from intestinal microvilli. Most asymptomatic but depends on worm burden and stage  Infected by walking over infected feces barefoot (it penetrates intact skin)  Skin manifestations where hook worm penetrates (dermatitis)  Pulmonary symptoms (transient eosinophilia when larvae migrate through lungs on their way ot intestine), intestinal infection usually asymptomatic but heavy infestation causes anemia (CBC) Cut
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