Schistosomiasis
Q. 1 Schistosomiasis infects humans at which of the following stages of it’s life cycle?
| A | Egg | |
| B |
Miracidia |
|
| C |
Cercariae |
|
| D |
All of the above |
Q. 1
Schistosomiasis infects humans at which of the following stages of it’s life cycle?
| A |
Egg |
|
| B |
Miracidia |
|
| C |
Cercariae |
|
| D |
All of the above |
Ans.
C
C
C
A
Explanation:
In water, eggs hatch to form miracidia, which invade snail. Cercariae from snail traverse human skin and vascular system.
Definitive diagnosis of schistosomiasis requires the recovery of the characteristic eggs in urine, stool, or biopsy specimens.
In S haematobium infections, eggs are most numerous in urine samples obtained at midday.
When examination of the sediment yields negative results, eggs may sometimes be recovered by filtering the urine through a membrane filter.
Cystoscopy with biopsy of the bladder mucosa may be required for the diagnosis of mild infection.
Eggs of S mansoni and S japonicum are passed in the stool. Concentration techniques such as formalin, ether or gravity sedimentation are necessary when the ova are scanty. Results of rectal biopsy may be positive when those of repeated stool examinations are negative.
Ref: Ray C.G., Ryan K.J. (2010). Chapter 56. Trematodes. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.
Q. 2
Water host required for schistosomiasis ‑
| A |
Fish |
|
| B |
Cyclops |
|
| C |
Snails |
|
| D |
Crabs |
Ans.
Explanation:
Ans. is ‘c’ i.e., Snails
Q. 3
Schistosomiasis is transmitted by ‑
| A |
Cyclops |
|
| B |
Fish |
|
| C |
Snail |
|
| D |
Cattle |
Ans.
Explanation:
Ans. is ‘c’ i.e., Snail
- The intermediate host for Schistosoma sp. is the snail.
- Schistosomiasis is an acute and chronic parasitic disease caused by blood flukes (trematode worms) of the genus Schistosoma.
- People become infected when larval forms of the parasite – released by freshwater snails – penetrate the skin during contact with infested water.
- Transmission occurs when people suffering from schistosomiasis contaminate freshwater sources with their excreta containing parasite eggs, which hatch in water.
- In the body, the larvae develop into adult schistosomes. Adult worms live in the blood vessels where the females release eggs. Some of the eggs are passed out of the body in the faeces or urine to continue the parasite’s lifecycle. Others become trapped in body tissues, causing immune reactions and progressive damage to organs.
Q. 4 Schistosomiasis is an example of:
| A |
Meta-zoonoses |
|
| B |
Cyclo-zoonoses |
|
| C |
Direct-zoonoses |
|
| D |
Sporo-zoonoses |
Ans.
Explanation:
Ans. a. Meta-zoonoses
Based Type of life cycle of infecting organism, zoonoses are divided into four categories:
1. Direct on the zoonoses-
- Transmitted from an infected vertebrate host to a susceptible vertebrate host by direct contact, by contact with a fomite or by a mechanical vector.
- The agent itself undergoes little or no propagative changes and no essential developmental change during transmission.
- Examples are → Rabies, Trichinosis, Brucellosis.
2- Cyclo-zoonoses
- Require more than one vertebrate host species, but no invertebrate host, to complete the developmental cycle of the agent.
- Example → Taeniasis, echinococcosis (hydatid disease).
3- Meta-zoonoses
- Transmitted biologically by invertebrate host
- Examples– Arbovirus infections, Schistosomiasis.
4- Sporo-zoonoses
- There is a non-animal development site or reservoir eg- organic matter (food, soil, plant)
- Example → Larva migrans and some mycoses.
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