Parasitology: Protozoan and Helminthic Parasites

Parasitology: Protozoan and Helminthic Parasites

• Emerging as serious threats in developed nations
• Parasites infect humans via ingestion, vectorborne transmission, or direct contact
• Arthropod vectors carry microbial pathogens
• Protozoa are unicellular eukaryotes

Protozoan Parasites of Humans

• Trophozoite: Feeding and reproducing stage within the host
• Cyst: Infective form; survives in the environment; develops into trophozoites after ingestion
• Parasites grouped by locomotion: ciliates, amoebae, flagellates, apicomplexans

Amoebae

• Water sources: Few cause disease
• Drinking contaminated water
• Excystment in small intestine; trophozoites migrate to large intestine
• Invasive amebic dysentery (severe diarrhea)
• Naegleria fowleri: Inhaled by swimmers; infects nasal mucosa, travels to the brain, feeding on brain tissue; 37 infections (2006-2015)

Flagellates

• Trypanosoma cruzi: Causes Chagas disease
• Opossums and armadillos are primary reservoir
• Feeds preferentially on blood vessels in the lips
• Myocarditis, asymptomatic chronic stage, congestive heart failure
• Leading cause of death in Latin America
• African Trypanosomiasis.
• Causative agent: Trypanosoma brucei gambiense

Other Protozoan Diseases

• Leishmania: Fatal in 95% of untreated cases
• Giardia: Ranges from asymptomatic infection to gastrointestinal disease
• Hydrogen sulfide detected in breath/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
• Plasmodium vivax: Fever every 2 days
• Plasmodium falciparum: Most deadly
• Anopheles mosquitoes transmit Plasmodium
• Parasite hidden from immune system while in erythrocytes;
• Induces "bite me" chemical signal in humans
• Genetic traits increase malaria resistance (sickle-cell trait)
• Death of brain tissue can be fatal within 24 hours
• Toxoplasma: Cats are the definitive host; alters rat behavior to be attracted to cat urine; may alter human behavior (men:introverted, suspicious; women: extraverted, trusting)

Helminths

• Toxoplasmosis: More severe in AIDS patients and fetuses; transplacental transfer can cause abortion, stillbirth, or various birth defects
• Macroscopic: 3 groups: Cestodes, Trematodes, Nematodes
• Cestodes (tapeworms): -Taenia saginata: Beef tapeworm -Taenia solium: Pork tapeworm -Diphyllobothrium latum: Fish tapeworm
• Trematodes (flukes): -Fasciola hepatica: Accidental definitive hosts in humans (blood, liver, lung, intestinal) -Schistosoma: Humans are the principal definitive host
• Nematodes (roundworms): -Ascaris lumbricoides: Most common nematode infection of humans -Enterobius vermicularis: (pinworms); usually asymptomatic; highly infectious -Ancylostoma duodenale: (hookworm) enters through feet; anemia, weakness, craving for peculiar foods (pica) -Trichinella spiralis: (trichinellosis), forms cysts in muscle tissue; encysted larvae ingested from undercooked pork and other meats

Explore the fascinating world of protozoan and helminthic parasites. This quiz covers their life cycles, modes of transmission, and the diseases they can cause in humans. Test your knowledge on the emerging threats posed by these parasites in developed nations.