Parasitology I

6 Pages

Microbiology and Immunology
Course Code
Microbiology and Immunology 2500A/B

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Lecture 5: Parasitology I 09/17/2012 *Not responsible for therapeutics Parasites  Ectoparasites – lice, fleas, flies that bite, poisonous spiders  Enteric protozoa  Blood and tissue protozoa  Helminths  Parasites have complicated life cycles  There are three types of symbiotic relationships – commensalism, mutualism, and parasitism  All infections are parasitic Enteric Protozoa  Often associated with travel, both domestic (e.g. camping) and foreign  Longer incubation period than bacteria and viruses  Symptoms may not develop until late in a trip or following return  Symptoms may be prolonged and/or recurrent o Depending on parasite, can be mild or severe  Presence of any protozoa (even nonpathogenic varieties) in stool indicates exposure to contaminated food or water  Cysts are the infective form, trophozoites are the active form  Diagnosis of parasitic infections depends on lab tests Etiology of Traveler’s Diarrhoea  Most are bacterial – 85%  Parasitic (protozoal or helminthic) – 5-15%  Viral – less than 5% Commonly Travel Associated Enteric Protozoa Less Common in Travelers  Giardia intestinalis most common  Cryptosporidium hominis & parvum  Entamoeba histolytica  Cyclospora  Dientamoeba fragilis  Isospora belli Diagnosis of Enteric Protozoa  Stools for ova and parasites  Examination of permanent stained smear is best o Sensitivity – what percentage of real infection does the test detect? o Specificity – what percentage of called positives are true positives?  There are many nonpathogenic enteric protozoa  Three negative stools to rule out pathogens  Five negative stools to rule out Giardia Giardia Intestinalis (Lamblia)  Worldwide problem via contaminated surface  Incubation period 9 – 15 days water (beaver fever – most common in waters  Soft, foul stools with flatus, bloating, gurgling, where Canadian beavers live) weight loss, fatigue  Infects duodenum  Residual lactose intolerance is common  Noninvasive  RXmetronidazole – therapeutic  Resistant to chlorination  Trophozoite is much bigger than the cyst  Iodination is more effective Entamoeba Histolytica  Worldwide  Symptoms range from nondysenteric (alternating constipation/diarrhea, lower abdominal cramps, bloating, flatus – not foul smelling – and fatigue) to dysentery  Colon ulceration may lead to systemic spread via bloodstream to liver, lungs, brain  Amebic serology is usually positive invasive disease  Phagocytized red blood cells in trophozoite – know this!  Peripheral chromatin around nucleus is evenly distributed in cysts Amebic Liver Abscess CT Scan  CT – computerized x-ray scans that express the body as if it has been sliced o View as if you’re looking from the feet end Amebic Liver Abscess  Right lobe abscesses respond to drug therapy  Left lobe abscesses need drainage as they tend to extend to the pericardium Entamoeba Dispar  Nonpathogenic species morphologically indistinguishable from E. histolytica  Can be differentiated by a rapid stool antigen test  Trophozoites do not have red blood cells Dientamoeba Fragilis  Amoeba-like noninvasive flagellate  No cyst form  Worldwide  May be transmitted on pinworm (Enterobius vermicularis) eggs  Diarrhea, bloating, flatus, fatigue  Fragile – has no cyst phase Cryptosporidium Parvum & Hominis  Only 10 oocysts needed for infection  Self limited diarrhea in normal hosts (7-30 days)  Short incubation period (4 days)  Intractable in AIDS patients, no good treatment  Found in many animals and birds (nitazoxanide)  Water contaminated with farm run-off, swimming pools, splash parks Cyclospora Cayetanensis  Incubation 2 – 11 days  Associated with import fruits  Watery diarrhea, indigestion, cramps, weight  Prolonged symptoms, 4 – 6 weeks loss, marked fatigue  Shows well with acid fast stain Isospora Belli  Rarely diagnosed  Symptoms similar to Giardia Blood and Tissue Parasites  Found in bloodstream and tissue  Plasmo
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