Parvovirus is common in Houston due to several factors. 1) Unlicensed breeders. Breeders that do not properly clean and sterilize their environments between litters may have parvovirus in their yard and in their home. Each litter becomes exposed, but symptoms do not show until 10-14 days after exposure. The greatest risk of parvo is during the "immunity gap." That occurs between 4 weeks, when the pups are being weaned, to 12 weeks, as their immune systems develop. 2) Large stray dog population. Stray, unvaccinated dogs may have other parasites such as hookworms or coccidia. These weaken the immune systems, making the dogs more susceptible to parvo. 3) Lack of education on proper shot protocols. Full vaccination requires 4 shots for puppies under 6 months, and a booster shot for adopted adult dogs over 6 months. Owners may not know the full vaccination regimen. And they may not know there are plenty of places for affordable vaccinations in Houston. 4) Cleaning protocols at shelters. Older shelters have cleaning systems that are inefficient. A mop and bucket can spread parvovirus across a kennel. A tiny spec of feces from an infected dog can infect an entire wing of a kennel, requiring cleaning with special products. This is 100% the opinion of HoustonDogMom. Let us know what you think the problem is in Houston! Email us at rebeccag @ houstondogmom.com.