Parasitology II

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Western University
Microbiology and Immunology
Microbiology and Immunology 2500A/B

Lecture 8: Parasitology II 09/26/2012 Helminths The Gang of Four: DALYs (Disability Adjusted Life Years)  HIV/AIDS – 84.5 million  NTDs – 56.6 million  Malaria – 46.5 million  TB – 34.7 million Neglected Tropical Diseases Group  Soil transmitted helminths (worms)  Other helminths  Protozoa  Bacterial infections 13 Core NTDs in Order of Prevalence 1. Ascariasis 6. Trachoma 11. African trypanosomiasis 2. Trichuriasis 7. Onchocerciasis 12. Buruli ulcer 3. Hookworm 8. Leishmaniasis 13. Dracunculiasis (almost 4. Schistosomiasis 9. Chagas disease gone) 5. Lymphatic filariasis 10. Leprosy NTDs  High prevalence  Associated with rural poverty  Ancient (not emerging)  Chronic disability and disfigurement  Low mortality Helminths MEMORIZE THESE THREE TERMS!  Nematodes (roundworms) – in cross section, are round (e.g. earth worms)  Cestodes (tapeworms) – segmented flat worms  Trematodes (flukes) – unsegmented flat worms Intestinal Nematodes  Enterobius vermicularis (pinworm)  Worms cannot reproduce in the body –  Ascaris lumbricoides whatever you get infected with in the  Trichiuris trichiura (whipworm) first place, is what you have  Hookworms  The longest a worm can live in one’s body  Strongyloides stercoralis is 8 – 9 years  Anisakis Enterobius Vermicularis  Pinworms  About 5 mm long, quite slender  Macroscopically visible  Harmless  Easy to see because they’re moving  Symptoms – itchy anus at night  Nocturnal pruitis ani when females migrate to perianal skin to lay eggs – live in the secum (large valve) – every night, females migrate and lay their eggs  Benign  Most common nematode infection in North America  30% of children infected worldwide  Scotch tape test – sticky side out, wrapped around a tongue depressor and used to find pinworms  Flat on one side and round on the other Soil Transmitted Helminths  Nematodes (roundworms) o Ascariasis o Hookworm o Trichuriasis (whipworm) Ascaris Lumbricoides  Large, about size of a pencil  Male and female ascaris  Normally harmless, unless there’s a lot of them – causes bowel destruction  One billion infected worldwide, #1 NTD  Adult worms live in the upper small intestine  Females produce enormous numbers of eggs which do not become infective until they are embryonated, 2 – 3 weeks in soil  Problems arise due to migration of adult worms and hypersensitivity to larvae in lungs Ascariasis: Pulmonary Phase  Cough, blood tinged sputum, wheezing, dyspnea + urticaria (hives)  Transient 30% - 50% eosinophilia o eosinophilia levels increase – good screening test  Transient pulmonary infiltrates Ascariasis: 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 common bile duct, pancreatic duct, appendix, etc. and cause obstruction Trichuris Trichiura  Whipworm  Light infections asymptomatic  Heavy infections – lead to dysentery and blood loss in the stool  Trichuris dysentery syndrome → anemia, rectal prolapse, finger clubbing and growth stunting  Rx: mebendazole or albendazole Intestinal Hookworms  Ancylostoma duodenale, Necator americanus  End up in bowels, sucking on the micro-villi that line the bowels  Heavy infestation – causes anemia  Light infestation – doesn’t really do any harm  About 25% of world population infected, 80% in some areas  Most asymptomatic but depends on worm burden and stage  Ground itch is first manifestation following skin penetration: maculopapular or vesicular pruritic dermatitis  Pulmonary symptoms (cough, wheezing, blood tinged sputum with transient eosinophilia) occur when larvae migrate through lungs on way to intestine  Intestinal infection usually asymptomatic but heavy infestation causes anemia Hookworm Management  CBC to check for anemia  Albendazole  Pyrantel pamoate (OK in pregnancy)  Mebendazole  Note: any of these simultaneously treat ascariasis and trichuriasis Cutaneous Larva Migrans: Ancylostoma brasiliense  Dog or cat worm  Cannot complete life cycle in humans  Crawl around and produces intense itchiness Strongyloides stercoralis  Exception to the rule that worms cannot reproduce in the body  Filariform larvae penetrate intact skin → pruritis and unusual skin eruptions  One of only two helminths that can reproduce in the body Strongyloidiasis Manifestations  Chronic skin: larva currens and stationary urticaria  Intestinal: diarrhea, abdominal pain and flatulence  Pulmonary: migration of larvae through lungs produces cough, wheezing and transient pulmonary infiltrates Hyperinfection Syndrome  Immunocompromised patients  May result in septic shock and death 
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