CPV2 is highly contagious and can be spread through direct contact, the fecal-oral route, or vectors such as fomites
CPV2 is shed in the feces of infected dogs within 4-5 days prior to the onset of clinical symptoms, throughout the period of illness, and up to 3 weeks after clinical recovery
After initial infection, the virus replicates in the lymphoid tissues of the oropharynx, mesentric lymph nodes and thymus, then spreads through the blood stream
CPV will infect and attack the rapidly dividing tissues or cells of the intestinal crypt, lymphopoietic tissue, and bone marrow
The viral attack on the intestinal crypt epithelium results in massive lysis and necrosis of enterocytes, which impairs the absorptive capacity, cell turnover at the villi tips, and results in the onset of diarrhea
In addition, the virus infects white blood cells (WBCs), in the bone marrow and lymphopoetic tissues, inducing lymphopenia and neutropenia, often resulting in the secondary infections
In 2-3 week-old puppies, often lacking maternally derived antibodies (MDA), CPV2 can replicate in cardiac cells, without signs of enteritis, and result in fatal myocarditis