Parvo is one of the most common causes of infectious diarrhea in young dogs. It is a devastating virus that can survive for many months in the environment and is difficult to destroy. It is most severe in young, rapidly growing pups that also harbor intestinal parasites (worms, coccidia, Giardia). It is highly contagious and easily transmitted through contaminated feces. It causes severe gastrointestinal signs (diarrhea, vomiting, dehydration, depression) and can also affect the heart muscle resulting in sudden death. The intestines become severely inflamed resulting in a condition called enteritis. Vaccinated females will provide protection (maternal antibodies) in the milk for their pups. This protection, however, inhibits the ability of the pup to develop its own protection in response to vaccination. At weaning, the maternal antibodies will gradually decline resulting in less protection, but allowing the pup to gradually respond to vaccination. The first vaccination takes at least a week to provide some protection, while booster vaccinations are necessary to provide increased levels of protection. These factors create a “window of susceptibility” to infection – maternal protection is gone and vaccine protection hasn’t developed. This is one of the reasons Parvovirus can still occur in spite of proper husbandry conditions. With the new high-titer, low-passage vaccines, the “window” is greatly reduced (but still present).