PRACTICE QUESTIONS

EXAM 1

Complete the following table.  Cells with  XXX do not require an answer.  Scientific names must be written correctly (Genus names capitalized and underlined; species name lower case and underlined)

Short Answer:  Read the paragraph below and then assess the statements below it.  For each statement, indicate if it is True or False and then justify your answer.  You must address each factor mentioned in the statements.  If you think an answer is false, then state what would be necessary to make it true.  It is possible for all statements to be true or false.

            Upon graduating from UNC Charlotte with a biology degree, you are accepted into a veterinary program in Johannesburg, South Africa.  As part of your training, you are required to work in a veterinary clinic.  During your residency, you are given the assignment of visiting a local poultry farm which is experiencing two major problems.  First, many of the young turkeys on the farm are dieing from a condition that causes bloody diarrhea and the skin on the head to turn black.  Second, the chickens are dieing in large numbers from an intestinal disease.  You conduct autopsies and fecal exams of both bird types.  You find large necrotic areas in the gut and liver of the turkeys, but no evidence of oocysts in the feces.  For the chickens, you find that the caeca are filled with blood and you find that the feces contain large numbers of oocysts.  Based on this information, you can correctly assume  (answers are given below):

a.  The black skin on the heads of the turkeys, coupled with the absence of cysts in the feces, indicates an infection of Nagleria flowleri, whereas the gut damage and presence of cysts in the chickens indicates an infection of Iodamoeba butschlii.

b.  The conditions in both bird species results from ingesting earthworms infected with dormant stages of the nematode, Enterobius vermicularis.

c.  In the life cycle of the chicken's parasite, metacyclic trypomastigotes injected by the vector invade host red blood cells, give rise to multiple sporozoites, which then invade gut epithelial cells and eventually form mature metacysts.  In contrast, in the life cycle of the turkey's parasite, amastigotes are released from ingested oocysts, invade gut cells, undergo repeated cycles of merogony and eventually give rise to an egg with a highly resistant shell that passes out with the host's feces.

d.  Both birds are infected with Trichomonas foetus, which causes gut damage and hemorrhaging in many species of birds.

ANSWERS

a.  False:  blackhead in turkeys caused by Histomonas meleagridis, which infects the caecum and live, does not form a cyst, but uses the egg of a nematode to transfer from host to host.  Nagleria flowleri in not a parasite of turkeys, but causes primary amoebic meningoencephalitis in humans.  Blood-filled caeca and presence of oocysts in chickens indicates infectin with Eimeria tenella; Iodamoeba butschlii is a parasitic amoeba that forms a cyst (not an oocyst), but is a parasite of humans, not chickens.

b.  False:  turkeys become infected with H. meleagridis by ingesting eggs of nematode Heterakis gallinarum, in which the larval nematode harbors the protozoan.  Chickens become infected with Eimeria tenella by ingesting an oocyst; a one-host life cycle that does not involve nematodes.  Enterobius vermicularis is the human pinworm, the eggs of which may transmit the parasite, Dientamoeba fragilis, to humans.

c.  False:   Life cycle of Eimeria tenella:  chickens ingest oocysts (there is no vector).  Sporozoites released from oocyst invade gut epithelial cells (not RBCs); metacyclic trypomastigotes are not part of Eimeria life cycle; are the infective stages of Trypanosoma spp. of the salivaria group.  Inside chicken's cells, undergo mergony giving rise to merozoites (not sporozoites); after 2-3 generations give rise to macro- and microgametocytes which fertlize and zygote forms an oocyst; metacyst is produced by the amoeba, Entamoeba histolytica. 

Life cycle of H. meleagridis:  turkey becomes infected by ingesting infected Heterakis gallinarum egg or earthworm (paratenic host) harboring infected nematode larvae; there is no oocyst in life cyle.  Egg or larval nematode releases the parasite in the turkey's gut, which then invades cells; there is no amastigotestage; this is found in the life cycle of Leishmania and Trypanosoma cruzi;   H. meleagridis does not undergo merogony (this is part of the coccidian life cycle; H. meleagridis is a flagellate); does not produce its own egg, but invades the ovary of H. gallinarum, becomes incorporated into the nematode's eggs, and uses resistant egg shell as a means to pass through environment.

d.  False, T. foetus is a sexually transmitted disease of cattle, not poultry, and causes abortion, not gut damage, and does not produce a cyst.