Parasitic Pathogens

Question 1

Describe the life cycle of common pathogenic protozoa, especially the sporozoa

Answer 1

Cyst: dormant infective stage
Trophozoite: feeding and dividing stage
Sexual reproduction: conjugation or gametogenesis
Asexual: fission or schizogony
Schizogony: multiple mitosis of nuclei followed by cytoplasmic segmentation (1 to many)
Sporozoa: immobile Asexual Reproduction- merozoite (adult) to schizont (multiplies via schizogony) to many merozoites
Sexual Reproduction- gametocytes meet (sex cells) form oocyst (cyst containing zygote) to sporozoites (spore-like stage infective)

Question 2

Define intermediate host and definitive (final) host

Answer 2

Intermediate host: host where larva live

Definitive host: host where adult lives

Question 3

List the common pathogenic protozoa, the diseases they cause, and their modes of transmission.

Answer 3

Entamoeba histolytica: causes dysentery (Montezuma’s revenge) ingestion of infected water
Trichomoniasis vaginalis: STD via sexual contact trophozoite
Giardia lamblia: diarrhea via infected water with cysts

Question 4

Compare in general terms the life cycles of nematodes and platyhelminths (trematodes and cestodes).

Answer 4

Nematodes (round worms): separate sexes do not need an intermediate host the eggs hatch in environment
Platyhelmiths (flat worms): Trematodes- hermaphrodites of separate sexes constantly in conjugation have intermediate host of snail and fish needs two
Cestodes- hermaphroditic eggs released in feces animal as intermediate host only needs one intermediate host

Question 5

Describe the major modes of transmission of common helminths

Answer 5

Fecal-oral
Injection by blood-sucking insect
Intermediate host (oral ingestion)
Active skin penetration

Question 6

Distinguish between intestinal and tissue infections by helminths

Answer 6

Intestinal infections: adults of nematodes and cestodes

Tissue infections: Larva of nematodes and cestodes; many adult trematodes