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Lecture 7

HSS1100 Lecture 7

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Health Sciences
William Yan

Lecture 7 -don't need to know lifecycles or taxonomy; don't really need to know about the drugs discussed -mutualism -> commensalism -> parasitism Parasitism -parasite is benefiting while host is not -1 sided relationship -short term (e.g.: mosquito) or permanent (e.g.: tapeworm in the gut) -extremely common way of life (50% of animals are parasitic at some stage in life) -nearly all organisms are parasitized at some point -true parasites include protozoans (single-celled eukaryotes), helminths (e.g.: tapeworms, roundworms, other worms), and arthropods (ectoparasites; parasitic on the outside of the body; i.e.: tics and mites) Slide 2 -success of parasites is defined in terms of: -prevalence in hosts -number of host species available -geographic range -number of offspring (higher = more success) -available routes of transmission (e.g.: water-borne transmission) Slide 3: -many are issues related to developing countries; determine likely hood and severity of infection -susceptible populations deals with immunocompromised patients Slide 4: -all of the enteric parasites are transmitted through person to person or water borne -person to person and water borne transmission are the most common -zoonotic deals with transmission from animals to humans -direct transmission from the handling of animals or their feces -indirect transmission from cattle manure into rivers and into the drinking water -insect vectors -congenital transmission from mother to fetus -penetration through skin -toxoplasma has many routes of transmission and this lends to its success Slide 5: -don't need to know names phyla or classes -know the terms flagellates, amoeba, ciliates, sporozoans, microsporidians -Balantidium is the only parasitic ciliates to humans -sporozoans cause the most severe symptoms in terms of public health -microsporidians are spore forming protozoans -similar to other enteric parasites Slide 6: -know the terms flukes, tapeworms, roundworms, etc. Slide 7: Giardia lamblia -the most frequently identified intestinal parasite worldwide -most infections are asymptomatic but are carriers; are the most dangerous in terms of epidemiology -cannot diagnose enteric parasites based on just symptoms because they are too vague -prevalence rises through infancy and wanes and the child reaches adolescence due to awareness of hygiene Slide 12 -many different strains / assemblages of Giardia found through DNA sequencing -knowledge of assemblage allows for knowledge of source of the Giardia -some are more dangerous than others -Giardia is quite resistant to chlorination Slide 14 -food is a vector for outbreaks Slide 15 -diagnosis is based on stool examinations -3 stool samples over a week since parasites are shed intermittently -samples are tested by microscopic methods in clinical labs using stains -fluorescent microscopy allows for better contrast Slide 16 -ELISA tests allow for detection of Giardia-specific antigens; not that commin Slide 17 -resistance to nitroimidazole and its derivatives is developing -don't need to know doses Slide 18 -resistance to chlorination -ozone and UV treatment are effective but expensive -EPA method 1623 is used to detect Giardia; based on microscopy Slide 19 -increasing awareness of person to person transmission (i.e.: handwashing) -many break outs in daycares, psychiatric facilities, and places with poor hygiene -washing produce reduces numbers of parasites and may help reduce risk -advice to travelers (avoid tap water in developing countries and peeled fruits) Slide 20 Trichomonas vaginalis -most common STD transmitted -also a flagellate -does not need an environmentally resistant cyst stage since it is transmitted through person to person contact (via mucous membrane contact) -increases susceptibility to cervical cancer and HIV infection -males can develop symptoms but are generally asymptomatic -diagnosis involves looking for trophozoids / trichomonads in vaginal or urethral discharge through microscopy -actively move around and are easy to spot -metronidazole are drugs of choice Slide 24 Entamoeba histolytica -likely to go beyond an enteric infection -likely to cause traveler's diarrhoea -transmitted through fecal-oral route and may be transmitted through other routes after -largely related to sanitation hygiene like most other enterics -may cause amoebic dysentery (bloody diarrhea) or may be asymptomatic -histoly
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