Bovine Viral Diarrhoea Virus (bvdv) Infection in Pregnant Cows and Their Foetuses

The aim of the study was to characterize bovine viral diarrhoea virus (BVDV) infection in pregnant cows and their foetuses. Blood samples from 64 clinically healthy cows, determined as pregnant after slaughter, and from their foetuses were collected into tubes with and without EDTA. In total 128 blood samples were examined for BVDV antibodies and 128 leukocyte samples for BVDV antigens by direct and indirect ELISA. Thirty-six out of 64 (56.25%) sera from adult cows were detected as seropositive while only one (1.56%) serum from a foetus was seropositive. Leukocyte samples from pregnant cows were negative for BVDV antigen while BVDV antigen was detected in only one (1.56%) leukocyte sample from a foetus. A foetus, 4-month-old, belonging to these of seropositive cows, was detected as BVDV antigen negative and antibody positive. The other one, 2-months-old, was found as antigen positive and antibody negative. Key word: cows, foetus, BVDV, ELISA. Bovine viral diarrhea virus (BVDV), an enveloped positive –strand RNA virus, is a common pathogen of cattle. The virus causes a wide range of clinical syndromes depending on age and immune status of the animal at the time of infection. BVDV is currently classified in the pestivirus genus of the Flaviviridae family, which also includes hog cholera and border disease viruses (12). Field isolates of BVDV can be divided into two biotypes according to their ability to induce cytopathic effect in bovine cell cultures: cytopathic or non-cytopathic. When a seronegative pregnant cow is infected with a non-cytopathic BVDV biotype, the virus can be easily transferred to the foetus. Infections during the foetal life lead to abortion, mummification, teratogenesis or persistent infection of a calf (1). Persistently infected calves show immunological tolerance to the virus and may be born as apparently healthy animals. They shed the virus during their life being responsible for perpetuation of BVDV infection in cattle population. Fatal mucosal disease occurs only in persistently infected animals and is induced by the cytopathic biotype of BVDV. This event may take place by mutation to the cytopathic biotype or superinfection with a cytopathic biotype of BVDV (3, 8). Material and Methods Animals. A total of 64 clinically healthy cows, determined as pregnant after slaughter, and their 64 foetuses were used in the study. The age of foetuses were calculated according to the method by Richardson et al. (22). Serum samples. In total 128 blood samples, which were taken from cows and foetuses into normal tubes during slaughter at slaughterhouse, were centrifuged at 1 500 2 000 rpm/15-20 min to obtain sera. The serum samples were kept in deep-freezer under -25°C and inactivated at 56 ̊C for 30 min before use. Leukocyte samples. Leukocytes were obtained from blood samples, taken after slaughter into tubes with EDTA (ethylendiamine tetraaceticacid), by centrifugation at 2 000-2 500 rpm/15-20 min and stored in deep freezer at -25°C till use. ELISA kits. Commercial direct and indirect ELISA kits (Institute POURQUIER) were used for the detection of BVDV antigens in leukocyte samples and BVDV antibodies in serum samples as described in the test procedure.