"There is nothing permanent except change" - Viral evolution.

The origin of seemingly new viral infections is not always clear. Such is the case with canine parvovirus.

I thought it appropriate to use the title of a paper published in the journal Veterinary Microbiology, as the title for this week's blog (Truyen et al., Vet Microbiol 1995 Feb;43(2-3):103-22). In response to last week's article Canine Parvovirus Infection, Rosemary asked a question in the discussion area on the origin of the parvovirus The origin of parvovirus. Canine parvovirus (CPV) was first detected in 1978 and since has become a widespread disease in domestic and wild dogs throughout the world. It is believed that CPV emerged from an ancestor virus similar to the feline parvovirus (FPV) that causes panleukopenia (abnormal decrease in all types of white blood cells resulting in an inability to defend against infection). Genetic analysis has shown differences of less than 1% between the 2 viruses (Parrish CR. Vet Microbiol 1999 Sep 1;69(1-2):29-40). So the short answer to Rosemary's question is that canine parvovirus is likely a mutation of the earlier feline parvovirus.

CPV has evolved since it was first detected, acquiring a broader host range and greater infectivity, and continues to evolve. Two new strains of the virus - CPV-2a and CPV-2b have replaced the original CPV-2, and these new strains have the ability to infect cats (Parrish CR. Vet Microbiol 1999 Sep 1;69(1-2):29-40). It is interesting that parvovirus initially infected cats only, then mutated resulting in a new strain that caused infection only in the canine family, and now has mutated again so that it has the ability to infect both felines and canines. Viral evolution is fascinating - whereas humans are likely only to live long enough to see three generations of their family reproduce, viruses replicate so rapidly and in such great numbers that mutations or changes occurring in each new generation appear seemingly instantaneously. This is one of the reasons why microbiologists are so concerned that changes in the avian influenzae virus may result in a world-wide pandemic in humans.