What is the infective stage of Schistosoma species?

The infective stage of Schistosoma species is the cercariae. These are free-swimming larvae that emerge from the intermediate host, which is typically a freshwater snail. When a person comes into contact with contaminated water, the cercariae can penetrate the skin, leading to infection.

This life cycle is crucial to understand because it highlights the environmental conditions that allow for transmission and the specific stages at which intervention might occur. For instance, knowing that cercariae are responsible for initiating the infection underscores the importance of avoiding exposure to contaminated water in endemic areas. The other options, while part of the life cycle of Schistosoma, do not represent the stage that actively infects the host. Eggs are laid by adult worms in the host and eventually hatch into miracidia, which then find the intermediate host. Adult worms reside within the human host's blood vessels. Larvae, in this context, refer to the stages of development prior to cercariae and are not directly infective to humans.