Abstract. The clinical signs, hematologic changes, serum and fecal virus titers, specific antibody production and the occurrence of histologic lesions were studied in 22 nine-week-old seronegative beagle dogs inoculated by the oral and intravenous route with canine parvovirus. Approximately 30% of the dogs had clinical signs of pyrexia, depression, vomiting, and diarrhea irrespective of the route of inoculation. Events in the dogs inoculated intravenously preceded those in dogs inoculated orally by approximately two days. Only one dog died. Lymphopenia was the most consistent hematologic change. Viremia always preceded the initiation of fecal virus shedding. Viral titers in the serum and feces were significantly greater in symptomatic dogs compared to asymptomatic dogs. Termination of the plasma viremia coincided with the onset of the humoral immune response, but viremia persisted one day longer in symptomatic dogs. The severity of lymphoid tissue and intestinal infection, assessed by tissue immunofluorescence and histology, was also greater in symptomatic dogs. The severity of intestinal disease was highly correlated with the magnitude and duration of viremia.The clinical signs, clinicopathologic and pathologic changes in fatal cases of naturally occurring canine parvovirus enteritis have been well-do~umented.~~~.Fatal cases are characterized by leukopenia and extensive necrosis of intestinal gland epithelium and lymphoid tissues. Although subclinical infection with canine parvovirus is less wellcharacterized, serologic evidence and limited epidemiologic s t~d i e s '~. ' ' ,~~ suggest that canine parvovirus infection more frequently results in subclinical than fatal disease. Similarly, experimental canine parvovirus enteritis infrequently results in severe clinical disease. Severe illness has been experimentally produced by intravenod5 and by oronasal and intraga~tric'.~~ inoculation of puppies. In the later clinical signs occurred only in dogs vaccinated with a mixed vaccine five days prior to canine parvovirus inoculation. Factors associated with the variation in the severity of the enteric disease in both the experimental and the natural setting have not been identified.This study was undertaken to determine the pathogenesis of experimental canine parvovirus enteritis and to identify factors associated with its variable severity. Materials and MethodsEighteen conventional and ten specific pathogen free seronegative nine-week-old beagle dogs were housed in individual 10. 13. 14. 16. 18.21.23.25.26.28.30.32.39.4l cages within isolation units, fed commercial dry dog food, and provided water ad libitum.Following a 12-hour fast, seven conventional and four specific pathogen free dogs were inoculated orally, and an equal number intravenously with I O5 tissue culture infective doses (TCID5,J of canine parvovirus. Four conventional and two specific pathogen free dogs were uninoculated controls. Rectal temperatures and clinical signs were recorded daily.Blood and fecal samples were collected daily for three days ...
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.
Abstract. Myocarditis was produced in seronegative five-day-old pups by oral and by intraperitoneal inoculation of canine parvovirus. The disease was subclinical. Histologic lesions were compatible with, but less extensive than, those seen in naturally occumng canine parvoviral myocarditis. In pups necropsied 23 days after inoculation, scattered cardiac myocytes contained intranuclear inclusion bodies, and virus-infected myocytes were demonstrated by immunofluorescence. Degeneration and loss of cardiac myocytes usually was not associated with a cellular infiltrate. At 51 days after inoculation, the myocardium contained an extensive lymphocytic infiltrate which was sometimes associated with fragmented myocytes, and was often contiguous with areas of interstitial fibrosis. At 108 days after inoculation, inflammatory lesions had regressed, and there were multifocal areas of myocardial fibrosis.
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