What method is primarily used by schistosomes to infect new hosts?

Schistosomes primarily use direct skin penetration as their method of infecting new hosts. These parasitic worms have a life cycle that involves larvae, known as cercariae, which are released from freshwater snails. When humans come into contact with contaminated water, the cercariae can penetrate the skin readily. This ability to directly penetrate the skin allows them to efficiently enter the host's body, where they then migrate through the bloodstream.

This mode of infection is particularly effective because the larvae are adapted to burrow into the skin, utilizing specific enzymes to facilitate their entry. Once inside, they are able to mature into adult worms that can cause various health issues. Other methods listed, such as ingestion of infected food or inhalation of larvae, are not typical transmission routes for schistosomes, highlighting why direct skin penetration is the correct answer.