Canine Parvovirus (CPV)

Canine Parvovirus (CPV)

In dogs, Parvovirus should be suspected whenever puppies are presented with lethargy, vomiting, &/or loose stools especially if there is blood in the stool (a hemorrhagic enteritis). Puppies 6 to 16 weeks of age are the most susceptible. This is due to the fact that puppies younger than this are usually protected by maternal antibodies they received in the mother’s milk (colostrum). Older dogs have acquired immunity from vaccination or previous exposure and may not show significant clinical illness if they do become infected. Rottweilers, Doberman Pinschers, and English Springer Spaniels seem to be at greater risk for severe disease, but we see this devastating disease an all species of dogs.

CPV infects rapidly dividing cells of the intestine, bone marrow, and lymphatic tissues. The rapidly dividing cells of the intestine reside in valleys of the intestinal mucosal lining known as crypts. These cells then migrate to cover the hills of the mucosa known as villi. The virus is capable of severe enough damage to result in necrosis (cell death) of the intestinal crypt cells and this leaves no cells to cover the villi. The villi essentially are ulcerated, collapse, and digestive function is lost. Tremendous amounts of blood components and fluids are lost across this ulcerated mucosa and toxins and bacteria may be free to pass from the intestinal lumen to the bloodstream.
Rapidly dividing cells are also found in the bone marrow and the virus attacks these resulting in a drop in the dog’s white blood cell count. Both lymphocytes and neutrophils are affected (these are types of white blood cells). Neutrophils are the predominant white blood cell found in circulation and function as part of the rapid first line of defense against infection. CPV infection causes low neutrophil counts by cell injury in the bone marrow and due to depletion of circulating cells responding to the tremendous amount of damage to the intestinal wall. The lower the white blood cell count, the worse the illness and counts less than 3000 mean the dog is not able to defend against bacteria found in the digestive tract and the environment.