科研之友
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摘要
Background: Bovine viral diarrhea virus (BVDV) refers to a heterogeneous group of viruses belonging to the family Flaviviridae and genus Pestivirus. This family of viruses is one of the main pathogens of cattle and causes significant economic losses to the cattle industry worldwide. BVDV is an enveloped virus with a diameter of 45 nm and single-stranded RNA genome of 12.5 kb. BVDV infection has been associated with a number of clinical manifestations ranging from unapparent infection and mild signs to acute illness and death. In general, calves are more susceptible to BVDV infection, but adult cattle can develop the clinical disease if they are infected with highly virulent virus strains. This study describes clinical, anatomopathological and epidemiological findings of a BVDV outbreak in calves in the state of Mato Grosso do Sul, Brazil.
Materials, Methods & Results: The outbreak occurred in the town of Agua Clara in the state of Mato Grosso do Sul. Epidemiological and clinical data were collected by the farm manager during a visit to the property. The outbreak involved two Nelore heifer calves that died between 30 and 40 days of age. One calf was taken to the Laboratory of Pathological Anatomy (LAP) of the Faculty of Veterinary and Animal Husbandry, Federal University of Mato Grosso do Sul (FAMEZ/UFMS). The calf was necropsied, and white streaks were seen on the heart, indicating congestive failure with swelling of body cavities and congestive hepatopathy (nutmeg liver). Fragments of different organs and tissues were collected during necropsy, fixed in 10% formalin for 48 h, embedded in paraffin, cut in 5 mu m sections and stained with hematoxylin-eosin (HE) or analyzed by immunohistochemistry (IHC) in the Veterinary Pathology sector of the Federal University of Rio Grande do Sul (UFRGS). Histologically, the heart lesion was characterized by fibrous coagulative necrosis associated with marked infiltrate (predominantly lymphocytic) and some macrophages. The diagnosis was confirmed by immunohistochemical agent identification in Peyer's patches within the intestine.
Discussion: The diagnosis of congestive heart failure due to myocarditis caused by BVDV infection was confirmed by the IHC technique. While in other countries, myocarditis caused by natural infection in cattle and experimental infection in goats and sheep due to BVDV has been described, there have been no reports of this clinical and pathological manifestation of the disease in Brazil. The heart lesions observed in the outbreak should be differentiated from similar injuries caused by certain plants and from Neospora caninum infection. In the present study, while the virus was identified by immunohistochemistry only in Peyer's patches, BVDV was considered to be the cause of the cardiac lesions by a process of elimination and because there is no correlation between the amount of viral antigen and the location of histological lesions. Other studies have used the IHC technique to detect BVDV antigen in other tissues of cattle and observed that the antigen is not uniformly distributed among the organs, suggesting that no specific organ of aborted fetuses can be chosen for BVDV diagnosis. Immunohistochemistry was shown to be an efficient method for detecting the antigen in the Peyer's patches of infected calves. This is the first report of nonsuppurative myocarditis associated with BVDV causing perinatal cattle death with agent identification in Mato Grosso do Sul. However, these data are insufficient to determine the importance of BVDV infection in terms of reproductive losses in this state because the methodological approaches used were different from those adopted in earlier studies.
- 出版日期2013-1-23
