Tears are released in response to the presence of any irritants in the eyes. The tears are spread on the surface of the eyeball through blinking. In this way, tears keep on washing the surface of the eyes and prevent microbes to infect the same.
Tears also contain the enzyme lysozyme. Lysozyme is an enzyme that can digest the cell walls of some bacteria. Hence, invasion of certain bacterial species is prevented by innate immunity provided by lysozyme of tears.
Protozoan infection of the intestines. Giardiasis forms cysts and travel through the feces so anything that comes in contact with the feces and the animal has consumed it will host the parasite.
