Pathogenesis of Canine Parvovirus Enteritis: Sequential Virus Distribution and Passive Immunization Studies

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Abstract
After oral inoculation, the sequential distribution of canine parvovirus was studied in 14 nine-week-old seronegative beagle dogs. Two or three dogs were necropsied on days 1 through 6 after inoculation. Tissues were collected for virus isolation, immunofluorescence testing, and light microscopy. Virus was isolated from, and fluorescent cells were seen in the tonsil, retropharyngeal and mesenteric lymph nodes one and two days after inoculation. Virus infection of systemic and intestinal lymphoid tissues occurred as early as three days after inoculation and was associated with viremia. Intestinal epithelial infection was first seen four days after oral inoculation. All dogs were viremic before intestinal epithelial infection was found. Fecal virus excretion first occurred four days after oral virus inoculation. Intestinal virus infection and lesions became progressively more severe between four and six days after inoculation. The severity of intestinal lesions was variable and related to the severity of systemic lymphoid tissue lesions and the magnitude and duration of viremia. Four littermates of virus-infected dogs were passively immunized against canine parvovirus with convalescent canine serum 24 hours after oral virus inoculation. Neither clinical signs, lymphopenia, nor fecal virus excretion occurred in passively immunized dogs. Intestinal epithelial infection was not demonstrable by immunofluorescence testing when passively immunized dogs were necropsied four, five, and six days after virus inoculation.