The virus has 3 basic strains:
1. CVP2 which was the first one found in 1978
2. CVP2a came on the scene in the early 80's
3. The strain most prevalent today is CVP2b
Eventually a new strain will appear because the virus will adapt to the immune system of dogs.
The parvovirus can linger in the environment for many months, allowing it to affect other dogs. It can withstand common household disinfectants (except bleach) and can withstand freezing winter temperatures. It can be spread on the hair and feet of dogs, in addition to shoes, clothes, and eating utensils.
We tend to see parvo in dogs that have other diseases, especially
intestinal parasites (worms). This might be because these dogs have immune systems that are weakened, making them more susceptible to a viral infection. Also, the parvo virus capitalizes on the fact that the lining of the intestines of these dogs with intestinal parasites are damaged and susceptible to the parvovirus.