How do endoparasites typically enter a pet's body?

Endoparasites most commonly enter a pet's body through the ingestion of contaminated food or water. This route of transmission is particularly significant for a variety of parasites, such as gastrointestinal worms (like roundworms, tapeworms, and hookworms) and protozoans (like Giardia). These parasites often lay eggs or cysts that can contaminate the environment, including soil, food, or water sources. When pets consume these contaminated items, the parasites can establish themselves within the gastrointestinal tract and, in some cases, migrate to other body systems.

The other methods outlined in the options, while they can be involved in other types of infections or external parasites, do not typify the common mode of entry for endoparasites. For instance, while some parasites might enter through the skin, this is not typical for most endoparasites, which usually require ingestion for transmission. Similarly, air inhalation is not a pathway for endoparasites; this method might be relevant for respiratory pathogens, but not for those residing within the gastrointestinal system. Finally, contact with other infected animals can lead to a variety of infections, particularly with external parasites, but it is the ingestion of contaminated materials that primarily facilitates the infection process of endoparas