Which form of Schistosoma penetrates the skin?
cysts
miracidia
spores
cercariae
The correct answer and explanation is:
Correct Answer: Cercariae
Explanation:
The form of Schistosoma that penetrates the human skin is called the cercariae. Cercariae are the free-swimming larval stage of the parasite, released into freshwater by infected snails, which act as intermediate hosts. When humans come into contact with contaminated water, the cercariae actively seek out skin, attach to it, and then burrow through the skin to enter the bloodstream.
Once inside the body, the cercariae shed their tails and become schistosomula. These schistosomula travel through the bloodstream to the lungs and liver where they mature into adult worms. The adult worms then migrate to their final destination, typically the blood vessels of the intestines or bladder, depending on the species of Schistosoma involved. From there, they begin producing eggs that either exit the body through urine or feces or become trapped in body tissues, leading to inflammation and organ damage.
Other answer choices are incorrect for the following reasons:
- Cysts are not part of the Schistosoma life cycle. Cysts are typically associated with other parasites like Giardia or Entamoeba.
- Miracidia are the larval stage that hatches from eggs in water and infects freshwater snails. They do not infect humans.
- Spores are reproductive structures found in fungi and some protists, but they are not involved in the Schistosoma life cycle.
The ability of cercariae to directly penetrate human skin without requiring a bite or ingestion makes Schistosoma a highly transmissible parasite in endemic areas, especially where people bathe, swim, or work in contaminated freshwater. Preventing schistosomiasis includes avoiding contact with freshwater sources known to harbor the parasite and controlling the snail population.