Parasitology

Question 1

Adult Ascaris lumbricoides worms reside in the

a) Lungs
b) Liver
c) Small intestines
d) Large intestines

Answer 1

C - Small intestines

Ascaris lumbricoides is commonly known as the large intestinal roundworm. Although the larval form of Ascaris migrates through the lung, where it can cause Loeffler’s syndrome, the mature form lives in the duodenum or proximal jejunum within the small intestines. The adults are very large and can measure up to 35 cm in length (13 inches)

Question 2

Which one of the following parasites migrates through the circulation (blood) before maturing in the portal venous system

a) Schistosoma mansoni
b) Enterobius vermicularis
c) Taenia saginata
d) Trichuris trichiura

Answer 2

A - Schistosoma mansoni

S. mansoni is a fluke that resides in the portal system venules, primarily those in the lower intestine. Cercariae is released from infected snails (intermediate host) into freshwater estuaries. Humans that are in the water may become infected through skin penetration. The cercariae then enter the blood circulation, finally settling into the intrahepatic portal blood vessels of the intestine where it matures

Question 3

All of the following life stages of schistosomes are appropriately matched with the host they are found in except

a) Cercaria - cow
b) Sporocysts - snail
c) Adult worm - human
d) Egg - human

Answer 3

C - Cercaria - cow

Adult worms inside humans produce numerous eggs that are excreted in feces or urine. The eggs consist of a developed miracidium that emerges upon contact with fresh water. Select snail species serve as an intermediate host where the miracidium matures into sporocysts. The sporocysts divide into hundreds of cercariae that then serve as the infective stage for humans
Cows have no role in this life cycle

Question 4

What is the first stage of the Wuchereria bancrofti life cycle in human infections

a) The infective stage develops in insect
b) Ingested by blood-sucking insect
c) Mature in the circulatory system, body cavity, or connective tissue in humans
d) Microfilariae in blood or skin of humans

Answer 4

D - Microfilariae in blood or skin of humans

The mosquito is the intermediate host for the microfilaria and humans are the definitive host and the reservoir

1. Microfilariae in blood or skin of humans
2. Ingested by blood-sucking insect
3. Infective stage develops in insect
4. Enters new host human when insect takes blood meal
5. Matures in circulatory system, body cavity, or connective tissue
6. Adult worms found in humans

Question 5

Which of the following parasites have adult forms that are found in the lungs and eggs commonly recovered in sputum samples

a) Fasciola spp.
b) Clonorchis sinensis
c) Opisthorchis spp.
d) Paragonimus spp.

Answer 5

D - Paragonimus spp.

The only parasite listed that is commonly recovered from sputum species is Paragonimus spp.
Has a liver-lung migration pattern

Question 6

A 65 year old Asian female presented to the emergency room complaining of severe abdominal pain, fever, and diarrhea. Examination revealed an enlarged liver that was tender to the touch. The patient noted that she had worked in a fish processing plat for several years before moving to the United States. A significant component of her diet consisted of raw fish. Both stool and duodenal contents were collected and sent to the laboratory for culture and parasite examination. Bacterial clues were unremarkable, but a suspicious form measuring 27 um by 14 um was found microscopically in both specimens. What organism is most likely the cause for this patient’s symptoms

a) Clonorchis
b) Whipworm
c) Sheep liver rot
d) Hydatid cyst

Answer 6

A - Clonorchis

The patient most likely contracted the parasite Clonorchis sinensis from consuming infected raw fish. Thorough cooking of such fish prior to human consumption would have probably halted the Clonorchis life cycle and the patient would not have gotten ill

Question 7

What is the characteristic feature of the trophozoite stage for the intestinal flagellate Giardia duodenalis

a) Two nuclei
b) An undulating membrane
c) Two flagella
d) Lack of a sucking disc

Answer 7

A - Two nuclei

The trophozoite stage of the intestinal flagellate Giardia duodenalis is characterized by two nuclei and has been described as “someone looking at you”

Question 8

The eggs of which species of Schistosoma can be isolated from urine

a) S. haematobium
b) S. japonicum
c) S. mansoni
d) S. stercoralis

Answer 8

A - S. haematobium

Schistosoma haematobium migrates to the veins of the bladder so eggs are seen in the urine

S. mansoni goes to the veins of the large intestine and S. japonicum infects the veins of the small intestines, but both will shed eggs in the feces

Strongyloides stercoralis is not a schistosoma species, but rather a nematode