Most frequently, the parvovirus is passed to the cat or kitten when the animal inhales or ingests secretions from cats infected with the virus. The virus replicates within the tissues and then travels to the blood stream, where it continues to spread throughout the cat's body. The virus destroys the digestive tract and makes it unable to function normally: the intestines lose their ability to digest food or absorb any liquid or nutrients. As a result, vomiting and diarrhea often occur, causing severe dehydration that can be fatal if not treated.
The disease becomes more serious when it enters the cat's bone marrow, which manufactures the red and white blood cells and platelets. When panleukopenia reaches this stage, the cat may become very ill or die, since its capacity to fight off infection will be impaired by the decrease in white blood cells.
When a kitten becomes infected with the parvovirus while within its mother's uterus, part of its brain called the cerebellum may not develop normally, resulting in permanent brain damage. This condition, clinically known as cerebellar hypoplasia, can cause the animal to experience tremors in the head and have difficulty walking and maneuvering. Cerebellar hypoplasia does not grow more severe as the kitten matures, but the damage is permanent.
