Medical Microbiology: Parasitology Exam

Worms - Nematodes (Roundworms)

Unsegmented, cylindrical worms; example: Loa loa causes eye infections; diagnosed via blood smears; treated with ant-filarial

Worms - Trematodes (Flukes)

Leaf-shaped flatworms; example: Schistosoma causes schistosomiasis; larvae penetrate skin from contaminated water; leads to chronic pathology.

Worms - Cestodes (Tapeworms)

Segmented worms lacking a digestive tract; transmission via undercooked meat or the fecal-oral route.

Protozoa - Ameba

Single-celled; example: Naegleria fowleri, causes Primary Amebic Meningoencephalitis through nasal entry.

Protozoa: Ciliates

Covered in cilia; example: Balantidium coli, causes dysentery via contaminated food/water.

Protozoa: Flagellates

Protozoa that utilize one or more whip-like flagella for motility. They inhabit various niches, including intestinal tracts, urogenital tracts, and blood/tissues.

Protozoa - Sporozoa (Apicomplexa)

Intracellular parasites that lack locomotory organelles in their adult stages and possess an apical complex used for host cell invasion. Most feature complex life cycles involving both sexual and asexual reproduction across definitive and intermediate hosts.

Arthropods

Invertebrates with segmented bodies and exoskeletons; act as ectoparasites or vectors for pathogens; examples include mites (Sarcoptes scabiei) causing scabies, and numerous insect vectors transmitting various diseases.

Enterobius vermicularis (Pinworm)

Nematode; natural reservoir humans; transmitted via embryonated eggs (fecal-oral); pathogenic form is the worm; inhabits cecum/colon, causes perianal pruritus.

Ascaris lumbricoides

Nematode; giant intestinal roundworm; transmitted via ingestion of embryonated eggs in contaminated soil/food; larvae migrate through lungs before maturing in the small intestine.

Trichuris trichiura (Whipworm)

Nematode; transmitted via ingestion of embryonated eggs; adult worms reside in the large intestine/cecum, causing colitis and rectal prolapse in heavy infections.

Necator americanus / Ancylostoma duodenale (Hookworms)

Nematodes; transmitted when filariform larvae in soil actively penetrate human skin (usually feet); cause iron-deficiency anemia due to intestinal blood loss.

Strongyloides stercoralis

Nematode; threadworm; transmitted via skin penetration by filariform larvae; capable of auto-infection cycles in immunocompromised hosts.

Trichinella spiralis

Nematode; transmitted by ingesting encysted larvae in undercooked pork or game meat; larvae migrate and encyst in striated skeletal muscle.

Loa loa (Eye worm)

Nematode; transmitted by deerflies or blackflies (Chrysops); microfilariae circulate in blood during the day, adults migrate through subcutaneous tissues and conjunctiva.

Wuchereria bancrofti / Brugia malayi

Nematodes; filarial worms transmitted by mosquito bites; lodge in lymphatic vessels causing lymphatic obstruction and elephantiasis.

Schistosoma species (Blood Flukes)

Trematode; humans infected when free-swimming cercariae from freshwater snails actively penetrate skin; eggs trapped in tissues cause granulomas, fibrosis, and portal hypertension.

Clonorchis sinensis (Chinese Liver Fluke)

Trematode; transmitted by eating undercooked freshwater fish containing metacercariae; infects bile ducts, potentially leading to cholangiocarcinoma.

Fasciola hepatica (Sheep Liver Fluke)

Trematode; transmitted by ingesting metacercariae encysted on aquatic plants (e.g., watercress); infects liver parenchyma and bile ducts.

Paragonimus westermani (Lung Fluke)

Trematode; transmitted by eating undercooked freshwater crabs or crayfish; adults encyst in lung parenchyma, causing chronic cough and hemoptysis.

Taenia saginata (Beef Tapeworm)

Cestode; transmitted by ingesting encysted larvae (cysticerci) in undercooked beef; consists of scolex, neck, and proglottids absorbing nutrients directly.

Taenia solium (Pork Tapeworm)

Cestode; transmitted by undercooked pork (causing intestinal tapeworm) or fecal-oral ingestion of eggs (causing cysticercosis in tissues/brain).

Diphyllobothrium latum (Fish Tapeworm)

Cestode; largest human tapeworm; transmitted by eating undercooked freshwater fish; can cause vitamin B12 deficiency (megaloblastic anemia).

Echinococcus granulosus

Cestode; dogs are definitive host, humans accidental intermediate host; ingestion of eggs leads to slow-growing hydatid cysts in the liver and lungs.

Naegleria fowleri

Ameba; free-living in warm freshwater; trophozoites enter nasal mucosa while swimming and travel along olfactory nerve to cause rapidly fatal Primary Amebic Meningoencephalitis (PAM).

Entamoeba histolytica

Ameba; transmitted via ingestion of cysts in contaminated food/water; causes amebic dysentery and liver abscesses (anchovy paste exudate).

Acanthamoeba species

Ameba; free-living organism found in water/soil; causes amebic keratitis (associated with contact lenses) and Granulomatous Amebic Encephalitis (GAE) in immunocompromised hosts.

Balantidium coli

Only pathogenic ciliate infecting humans; pigs are primary natural reservoir; ingestion of cysts leads to trophozoites forming mucosal ulcers in the large intestine (balantidial dysentery).

Giardia lamblia (G. duodenalis)

Flagellate; transmitted via cysts in contaminated water; attaches to small intestine mucosa causing malabsorption, foul-smelling fatty diarrhea (steatorrhea), and cramps.

Trichomonas vaginalis

Flagellate; transmitted via direct sexual contact (no cyst stage); infects urogenital tract causing vaginitis, urethritis, and frothy yellowish-green discharge.

Trypanosoma brucei

Flagellate; transmitted by tsetse fly (Glossina) bite; causes African Sleeping Sickness with CNS invasion leading to sleep cycle reversal, neurological deterioration, and coma.

Trypanosoma cruzi

Flagellate; transmitted by triatomine bug ('kissing bug') feces rubbed into bite/mucous membranes; causes Chagas disease damaging cardiac tissue (megacardium) and GI tract (megaesophagus).

Leishmania species

Flagellate; transmitted by female phlebotomine sandfly bite; infects macrophages, causing cutaneous, mucocutaneous, or visceral leishmaniasis (kala-azar).

Plasmodium species (P. falciparum, vivax, etc.)

Apicomplexan protozoan causing malaria; transmitted by female Anopheles mosquito; erythrocytic cycle ruptures RBCs synchronously; produces hemozoin pigment crystals.

Toxoplasma gondii

Apicomplexan protozoan; felines are definitive host, humans intermediate host via undercooked meat/cat feces; poses severe congenital/teratogenic risks (hydrocephalus, chorioretinitis).

Cryptosporidium parvum

Apicomplexan intestinal coccidia; transmitted via waterborne oocysts; causes self-limiting watery diarrhea in immunocompetent, but severe chronic diarrhea in immunocompromised (AIDS).

Cyclospora cayetanensis

Apicomplexan intestinal coccidia; transmitted via contaminated food/water; causes prolonged watery diarrhea, fatigue, and weight loss.

Sarcoptes scabiei

Arachnid mite; obligate ectoparasite that burrows into the stratum corneum of human skin, laying eggs and causing intense nocturnal pruritus (scabies).

Ixodes / Dermacentor Ticks

Arachnid vectors; transmit bacterial and rickettsial pathogens such as Borrelia burgdorferi (Lyme disease) and Rickettsia rickettsii (Rocky Mountain spotted fever).

Anopheles, Aedes, Culex Mosquitoes

Insect vectors; transmit major pathogens including Plasmodium (malaria), Dengue, Zika, Yellow Fever, and West Nile virus.

Glossina (Tsetse Fly)

Insect vector; transmits Trypanosoma brucei (African Sleeping Sickness) through saliva during blood meals.

Triatomine Bug ('Kissing Bug')

Insect vector; transmits Trypanosoma cruzi (Chagas disease) by depositing infectious feces near bite wounds.

Phlebotomus (Sandfly)

Insect vector; transmits Leishmania species causing cutaneous and visceral leishmaniasis.

Chrysops (Deerfly / Blackfly)

Insect vector; transmits Loa loa (eye worm) microfilariae during daytime blood meals.