Parasites Flashcards
Helminths
- worms
- reproduce sexually, usually within host
Protozoa
- unicellular
- replicate quickly and asexually in host
Cestodes
- tapeworms
- hermaphroditic
- segmented
- eg. Taenia solium
- infection by egg/larval ingestion
Nematodes
- unsegmented
- roundworms
- sexes separate
- eg. Strongyloides stercoralis, Ascaris lumbricoides
Trematodes
- flat worms or flukes
- unsegmented
- hermaphroditic
- go through intermediate hosts: snails, shellfish
- eg. Schistosoma spp.
Schistosomiasis Life Cycle
- eggs hatch in environment producing miracidia
- miracidia infect snails
- cercariae leave snails and penetrate skin of human
- becomes schistosomulae and enters circulation, migrates to portal blood of liver
- paired adult worms migrate to venules of rectum and bowel, lay eggs that go through liver and are excreted into environment
Schistosomiasis Clinical Presentation
- 4 weeks post exposure presents as traveler’s diarrhea, urticaria, eosinophilia
- chronic pathology due to egg production, lost eggs can irritate mucosa, retained eggs can become obstructive, can affect liver function (portal hypertension)
Schistosomiasis Distribution
- mostly in Africa
- some in Asia and South Africa
Schistosomiasis Treatment
- population based treatment is best
- treat school aged children with antihelminths
Strongyloides stercoralis Life Cycle
- larvae excreted in stool
- larvae develop into adults, reproduce sexually
- larvae mature into filariform larvae that penetrate skin and initiate infection
- filariform larvae hematogenously spread to lungs, get coughed up and swallowed into intestine
- develop into adults, adult female produces eggs that develop into larvae
- larvae either excreted or auto infect and restart cycle without leaving human
Strongyloidiasis
-autoinfection can lead to hyper infection, producing GI hemorrhage, pneumonitis
Malaria
- most important parasitic disease worldwide
- majority of deaths in sub-Saharan Africa
Malaria Vector
Female anopheles mosquito
Malaria Parasite
-Plasmodium species (falciparum, vivax, knowlesi, ovale, malariae)
Schizogany
-asexual cycle in RBC’s and other tissues