Well established protozoan disease transmitted through milk, . . . . . . . .

Well-established protozoan disease transmitted through milk is Toxoplasmosis.
Toxoplasmosis is a parasitic disease caused by Toxoplasma gondii, an apicomplexan. Infections with toxoplasmosis are associated with a variety of neuropsychiatric and behavioral conditions.
It is usually spread by eating poorly cooked food that contains cysts, exposure to infected cat feces, and from an infected woman to their baby during pregnancy.