The Denver Animal Shelter is offering free parvovirus vaccinations for dogs under one year old for the entire month of May.

Canine parvovirus is a severely contagious, preventable virus that is often fatal in young dogs. The virus attacks a dog's gastrointestinal tracts and is transmitted through the feces and vomit of infected dogs and puppies. Parvo can live in feces about two weeks, but can live longer in the environment for many months.

Even though puppies are most at-risk for contracting the virus, all unvaccinated dogs can be affected. Common symptoms include lethargy, loss of appetite, fever, vomiting and severe diarrhea.

If your dog has similar symptoms, immediately go to your veterinarian.

Denver Animal Shelter says they have seen 15 cases of parvo so far this year.

The free vaccinations are offered in May on a walk-in basis Monday through Friday from 12 to 5 p.m. and Saturday and Sunday from 12 to 4:30 p.m. The shelter is located at 1241 West Bayaud Ave.