Parasitology Basics Quiz

Medically Important Parasites

• Parasites can be unicellular (protozoa) or multicellular (helminths, or worms).
• Protozoa are categorized into Sarcodina (amoebas), Sporozoa (sporozoans), Mastigophora (flagellates), and Ciliata (ciliates). Examples include Entamoeba histolytica and Giardia lamblia.
• Metazoa are subdivided into two phyla: Platyhelminthes (flatworms) and Nemathelminthes (roundworms). Cestoda (tapeworms) and Trematoda (flukes) are examples of flatworms.

Protozoa

• Entamoeba histolytica causes amebic dysentery and liver abscess.
• The life cycle has two stages: trophozoite (motile) and cyst (nonmotile).
• Transmission is often through contaminated food or water.
• Protozoa are often transmitted through food and water contaminated with fecal matter.

Intestinal & Urogenital Protozoa

• Entamoeba histolytica is a major cause of intestinal and urogenital infections.
• It causes amebiasis, potentially leading to dysentery.
• Giardia lamblia, another important parasite, causes giardiasis, characterized by watery diarrhea.

Giardia lamblia

• Its life cycle involves two stages: trophozoite and cyst.
• The trophozoite is pear-shaped with two nuclei, four pairs of flagella, and a suction disk.
• Symptoms include watery, foul-smelling diarrhea, nausea, anorexia, flatulence, and abdominal cramps.

Trichomonas vaginalis

• Causes trichomoniasis, a sexually transmitted infection.
• It's a pear-shaped organism, with a central nucleus and four anterior flagella, and undulating membrane that extends about two-thirds of its length.
• Exists only as a trophozoite (no cyst stage).
• Symptoms in women include a watery, foul-smelling, greenish vaginal discharge accompanied by itching and burning.
• In men, the infection is usually asymptomatic, but about 10% have urethritis.

Malaria (Plasmodium spp.)

• Caused by four plasmodia: Plasmodium vivax, Plasmodium ovale, Plasmodium malariae, and Plasmodium falciparum.
• P. vivax and P. falciparum are the most common types.
• Vector and definitive host is the female Anopheles mosquito.
• The life cycle has two phases: sexual (in mosquito) and asexual (in humans). Transmission is from the mosquito bite.
• Symptoms can range from fever to severe complications.

Toxoplasmosis (Toxoplasma gondii)

• A zoonotic disease caused by the Coccidian protozoan Toxoplasma gondii.
• Transmitted through contaminated food\meat.
• Can be transmitted through the placenta, causing severe complications in pregnant women.
• Infections in healthy individuals are usually mild or asymptomatic, but infections in immunocompromised individuals can be serious.

Chagas Disease (Trypanosoma cruzi)

• Caused by T. cruzi parasite.
• Transmitted by the reduviid bug (Triatoma).
• The life cycle involves the insect as the vector.
• Symptoms can range from acute to chronic; chronic Chagas disease is often associated with severe cardiac complications.

African Trypanosomiasis/Sleeping Sickness (Trypanosoma spp.)

• Caused by T. gambiense and T. rhodesiense parasites.
• Transmitted by the tsetse fly.
• Symptoms range from fever and headache to severely debilitating symptoms associated with brain and organ involvement.

Leishmaniasis (Leishmania spp.)

• Caused by the unicellular, flagellate, intracellular protozoa in the genus Leishmania.
• Transmitted through sandfly bites.
• There are different forms (visceral, cutaneous, and mucocutaneous.)
• Different geographical types of leishmaniasis are associated with infection in dogs in those areas.

Trematodes (Flatworms)

• Trematoda (flukes) and Cestoda (tapeworms) are two groups of the platyhelminths.
• Schistosoma (blood flukes), Paragonimus (lung fluke), and Clonorchis (liver fluke) are important trematodes, often having many people infected, leading to morbidity and mortality.
• Transmission is frequently through contact with contaminated water.

Cestodes (Tapeworms)

• Consist of a head (scolex) and segmented body (proglottids).
• Humans usually acquire tapeworm infections by consuming undercooked meat.
• Important cestodes include Taenia solium, Taenia saginata, Diphyllobothrium latum, and Echinococcus granulosus.

Nematodes (Roundworms)

• Roundworms with a cylindrical body, mouth, and anus and are characterized by their highly resistant, non-cellular outer coating.
• Intestinal nematodes include Enterobius (pinworm), Trichuris (whipworm), Ascaris (giant roundworm), Necator and Ancylostoma (hookworms), Strongyloides (small, roundworm) and Trichinella.
• Important tissue nematodes are Wuchereria, Onchocerca, and Loa.
• Transmission of these roundworms commonly occurs via ingested contaminated food or water.

Important Notes

• Parasite transmission often involves both a human host and an intermediate vector (like an insect)
• Transmission to humans can often occur through exposure to contaminated food, water, or the environment.