PET GUARDIANSHIP

The Parvo virus is a potentially fatal virus that is easily contracted by puppies who have been improperly vaccinated as well as by puppies under 12 weeks of age. When your young puppy goes to the vet they receive a vaccination against Parvo, however, due to their tiny little immune systems these vaccinations need to be boostered every two weeks until they are four months old for your pup to be as protected as possible.
Parvo easily lives on surfaces and can survive for incredibly extended periods of time. It can be spread as easily as you stepping on it outside and bringing it into your home on the bottom of your shoe. Parvo attacks the gut. A sick animals health will very quickly decline as it sheds its intestinal lining. 
While your pup is under 4 months, you should severely limit their exposure to the outside world. This means exactly what you think it means. No dog parks or walks around the neighborhood. No friends over and no under vaccinated dogs. In rescue we have a 'No Paws On The Ground" rule that is observed when transporting puppies. Whether that means bringing them from their kennel to a client in a shelter or bringing them from a foster home to their forever home, we carry these puppies and its not just because they're oh so friggen cute and cuddly. It's because as soon as their paws hit the ground of a high traffic area, they are potentially at risk.
Symptoms of a parvo dog include: rapid health decline with vomitting, diarrhea, lack of appetite, fever and more.