Aspectos clínicos e virológicos da infecção de bezerros por um isolado brasileiro do vírus da diarreia viral bovina

Abstract

The bovine viral diarrhea virus (BVDV) is considered an important pathogen of cattle and are widespread in the Brazilian herd. Transmission of the virus occurs by direct and indirect contact between infected and susceptible animals, and the persistently infected animals are essential in the maintenance of virus in the herd. The experimental reproduction of infection allows the study of clinical and viral parameters as well as setting parameters for diagnostic testing of vaccines and the determination of control measures. In order to study the pathogenicity of a sample of Brazilian BVDV-1a 241.10 four cattle were inoculated intranasally with a viral suspension containing 107.2 TCID50 / ml. One non-inoculated cattle was kept in contact with the inoculated cattle to assess the transmissibility. After inoculation, the animals were monitored daily to observe clinical signs. Samples of nasal secretions were collected on days -3 to 15 post-inoculation (pi) and blood on days -2, 0, 2, 4, 6, 8, 10, 12 and 14 pi for detection of viral presence by isolation in cell culture. The total leukocyte count was performed at different moments on days -3, 0, 3, 6, 9, 12, and 15 pi. The detection of antibodies was performed in serum at 7 day intervals until the 42 day post-inoculation. After inoculation no clinical signs were observed, only nasal and ocular serous secretion between days 1 and 5 pi and discreet cough between day 2 and 4 pi. Body temperature increased slightly between day 4 and 6 pi. Animal Control did not develop any of the signs observed in the infected group. The viral detection in the blood showed the presence of viremia between 4 and 8 days pi and nasal secretions between day 1 up to 10 pi. Virus was not isolated in the blood and nasal secretions of the animal contact, demonstrating the absence of transmission. In animals inoculated it was observed there was a reduction in total leukocyte count between day 3 up to 12 dpi. Neutralizing antibodies initially were detected on day 14 pi in all inoculated animals and remained until day 42 post-inoculation. The detection of anti-p80 antibodies occurred in two animals on day 14 post-inoculation and on day 42 post-inoculation all animals seroconverted. Animal Control did not develop antibodies at any moment. Therefore, it is concluded that the BVDV sample used for infection has low pathogenicity and reduced capacity of transmissibility for animal contact. Thus, the spread of infection can occur in the cattle population in a discreetly way and difficult perception.