Introduction to Human Parasites

Question 1

What are the biological groups of helminths that cause parasitic disease is humans

Answer 1

1. Roundworms/Nematodes (Ascaris, pinworms, whipworms, hookworms, Strongyloides, Echinococcus)
2. Flatworms/Trematodes/Flukes (Schistosomes, lung fluke, etc.)
3. Tapeworms/Cestodes (beef tapeworm, pork tapeworm, fish tapeworm, etc.)

Question 2

What are the biological groups of protozoan parasites that cause disease in humans

Answer 2

1. Amebas (Entamoeba histolytica, etc.)
2. Flagellates (Giardia, Trichomonas, Trypanosoma, Leishmania, etc.)
3. Ciliates (Balantidium coli)
4. Sporozoa (Cryptosporidium, Cyclospora, Plasmodium, Toxoplasma, etc.).
5. Microsporidia (Enterocytozoon, Septata, etc.)

Question 3

Schistosomiasis

Answer 3

Transmitted in humans by exposure to contaminated fresh water. (flatworms)

Life cycle:

1. ) Eggs shed in feces or urine of infected humans hatch in water and release miracidia, which infect snails.
2. ) Develop as sporocysts in snails, free-swilling cercaeriae are released.
3. ) Free- swimming cercaeriae penetrate human skin, lose tails and develop into schistosomulae in tissue of human host.
4. ) Gain access to blood system, mature into adult worms that migrate to mesenteric veins or venous plexis of bladder

Can cause swimmer’s itch within 2-3 days. Acute phase is serum-sickness like over 4-8 weeks after invasion. Chronic phase has glranulomatous and fibrotic changes to the liver or bladder.

Question 4

Malaria

Answer 4

Four species (plasmodium protazoa) cause disease in humans: P. vivax, p. ovale, p. malariae, and p. falciparum.(falciparum causes most of the death)

Life cycle:

1. ) Infected mosquitos bite humans, inject sporozoites into the blood.
2. ) Asexual phase of development occurs in humans. Can infect liver cells and replicate (only vivax and ovale can establish dormant hepatic phase, can initiate late relapses)
3. )After primary replication in liver, released into blood, infect erythrocytes and undergo asexual reproduction. Gametes formed in some infected RBCs.
4. )Sexual phase occurs in infected mosquitos where gametes fuse in intestine to form zygotes.

Symptoms of malaria primarily associated w/ rupture of infected erythrocytes and release of merozoites. (falciparm can invade ALL RBCs, both young and old)