Microbio - Ch. 23 Notes PDF

Parisitology: protozoan and helminthic parasites - emerging as serious threats in developed nations - parasites can infect humans by ingestion, vectorborne transmission, and direct contact Arthropod vectors: vectors are animals that carry microbial pathogens Protozoan parasi...

Parisitology: protozoan and helminthic parasites - emerging as serious threats in developed nations - parasites can infect humans by ingestion, vectorborne transmission, and direct contact Arthropod vectors: vectors are animals that carry microbial pathogens Protozoan parasites of humans: protozoa are unicellular eukaryotes - trophozoite: - feeding and reproducing stage that lives within the host - cyst: infective form that survives in the environment; undergoes excystment when ingested, developing into trophozoites - parasites classically grouped by their mode of locomotion (ciliates, amoebae, flagellates, and apicomplexans) - amoebae: - water sources; few cause disease - drinking contaminated water - excystment occurs in small intestine (trophozoites migrate to the large intestine) - invasive amebic dysentery (severe diarrhea) - Naegleria fowleri: swimmers inhale; protozoan infects the nasal mucosa from swimming water, penetrates the brain, and feeds on brain tissues; 2006 – 2015: 37 infections - Flagellates: - Trypanosoma cruzi: causes Chagas’ disease; Opossums and armadillos are primary reservoir; “kissing bugs” feed preferentially from blood vessels in the lips - myocarditis; asymptomatic chronic stage; congestive heart failure; parasite-induced heart disease is a leading cause of death in Latin America - African Trypanosomiasis - causative agent: Trypanosoma brucei gambiense  - second stage: mental deterioration and neurologic problems. Death in months - prevention: minimize contact with tsetse fly - death can occur within a few months of disease onset - Leishmania: fatal in 95% of untreated cases - Giardia: giardiasis ranges from asymptomatic infection to gastrointestinal disease - hydrogen sulfide detected in the breath or stools; beavers are a common reservoir - Trichomonas vaginalis: most common protozoan causing human disease in industrialized nations - transmitted almost exclusively via sex - treated with nitroimidazole drugs - Apicomplexans: Plasmodium - malaria - Plasmodium vivax: fever every 2 days - Plasmodium falciparum: most deadly - Anopheles mosquitoes have vectors for Plasmodium - parasite hidden from immune surveillance when in erythrocytes - induce “bite me” chemical signal in humans - genetic traits increase malaria resistance in endemic areas: sickle-cell trait - death of brain tissue can be fatal within 24 hours - Apicomplexans: Toxoplasma - cats are the definitive host - alters behavior in rats to be attracted to cat urine - may alter human behavior – infected men tend to be introverted, suspicious and rebellious, whereas infected women tend to be extraverted, trusting and obedient  - toxoplasmosis is more severe in 2 populations: AIDS patients, fetuses - transplacental transfer of the protozoan can cause abortion, stillbirth, or various birth defects - Helminths: - are macroscopic - 3 groups: Cestodes, Trematodes, Nematodes - Cestodes: called tapeworms - Taenia saginata is the beef tapeworm - Taenia solium is the pork tapeworm - Diphyllobthrium latum (fish tapeworm); has shrimp intermediate host - Trematodes: - commonly called flukes (blood, liver, lung, intestinal) - Fasciola hepatica; humans are accidental definitive hosts - blood flukes: Schistosoma; humans are the principal definitive host - Cercariae burrow through skin of humans who contact contaminated water - Nemotodes: - commonly called roundworms - Ascaris lubricoides (roundworm), usually unnoticed until blocks intestines - most common nematode infection of humans worldwide - abdominal pain, nausea, vomiting, and intestinal obstruction can occur if the worm burden is high - Enterobius vermicularis (pinworms), usually asymptomatic, highly infectious - humans are the only host - Ancylostoma duodenale (hookworm), enters through feet - anemia, lethargic behavior, and craving for peculiar foods (pica) - eggs hatch on ground, releasing larvae. Larvae enter through the soles of the feet and travel to the lungs. Ascend into throat to be swallowed - Trichinella spiralis (trichinellosis), forms cysts in muscle tissue - encysted larvae are ingested from undercooked pork and other meats