BOVINE VIRUS DIARRHEA

The infection caused by bovine diarrhoea virus (BVDV) generally causes mild clinical symptoms in immunocompetent cattle. A severe disease ca n be observed mainly in young animals. The infection of pregnant anima ls is especially important because the virus may invade the fetus. Due to an infection caused by a non-cytopathogenic BVDV strain persistent ly infected, immunotolerant animals may be born wich are consistently viraemic and can shed the virus during the whole lifetime. Such an inf ection can not be caused by a cytopathogenic biotype. Developmental di sorders of central nervous system and eyes may develop in case of an i nfection between the 90th and 150th days of pregnancy. The fetus is ab le to produce antibiodies against the virus during the second half of pregnancy. Venereal infections are also important. Bulls - in case of an acute infection with lower titres and for a shorter period, however in case of persistent infections persistently and with a higher titre - shed the virus. The virus in the semen may cause seroconversion, re turn to heat, embryonic disorders, etc. in the infected animals and th e animals born can be persistently infected. Mucosal disease (MD) may develop in animals persistently infected with a non-cytopathogenic BVD V during the fetal life - between the 40th and 120th days - when the a nimals are super infected with a cytopathogenic BVDV later on. When th e super infecting virus has a homologous antigenic structure a disease develops with low morbidity but high mortality. When the antigenic st ructure of the super infecting virus is partly heterologous, due to th e antibodies produced against it the super infecting virus disappear f rom the blood. MD develops weeks or months after the super infection. ND does nor develop after a super infection with homologous or heterol ogous cytopathogenic BVDV, even antibodies are produced against the he terologous virus. Diagnosis of the diseases caused by BVDV is based on the clinical symptoms, pathological and histological alterations and results of laboratory investigations. Demonstration of the virus, viru s antigen or nucleic acid are used for the laboratory diagnosis of BVD V.