A 6-week-old puppy presents with vomiting, diarrhea and leukopenia. What is the most likely diagnosis and confirmatory test?

• A. Canine parvovirus infection; fecal antigen ELISA or PCR for CPV
• B. Canine distemper; antibody titer
• C. Canine parainfluenza; chest radiographs
• D. Bacterial enteritis; fecal culture

Answer: (A)

Young puppies with vomiting and diarrhea who also have a low white blood cell count strongly point to canine parvovirus infection because CPV targets rapidly dividing cells, notably the intestinal crypts and bone marrow. This causes hemorrhagic, intractable diarrhea and leukopenia, which is a classic combo in a 6-week-old pup whose maternal antibodies are waning. To confirm the diagnosis, detect the virus in the intestinal tract: use a fecal antigen ELISA test or perform PCR on fecal material for CPV. Both methods are standard and useful—the ELISA gives a quick in-clinic result, while PCR is more sensitive. Antibody titers aren’t reliable for confirming an active infection, since they reflect exposure or vaccination rather than current disease. Parainfluenza is primarily respiratory, and bacterial enteritis wouldn’t typically produce the same severe leukopenia pattern or provide a straightforward confirmatory test for CPV.