Co-infection with bovine viral diarrhoea virus and Anaplasma marginale in a dairy cattle herd may lead to acute bovine anaplasmosis

This report describes an acute exacerbation of subclinical anaplasmosis manifesting itself in clinical signs in a large number of animals after infection with bovine viral diarrhoea virus (BVDV). The simultaneous transmission of BVDV and Anaplasma was unintended and most likely the result of a vaccination operation in a large Holstein-Friesian dairy cattle herd in Hungary. From Day 35 after the first vaccination, a total of 33 cows developed fever, depression, general weakness, lack of appetite, a sudden drop of milk production, anaemia, icterus, and tachypnoea on exercise. In addition, a total of seven abortions and three stillbirths occurred. Between Days 30 and 35 after the second vaccination four cows showed clinical signs typical of anaplasmosis, and two stillbirths occurred. The presence of Anaplasma marginale infection was demonstrated by haematological, biochemical, PCR and haemocytological examinations of blood samples collected from animals showing clinical signs as well as by necropsy. To assess the prevalence of infection in the herd, a specified number of animals belonging to different age groups were subjected to serological tests. The rate of seropositive animals was substantially higher (50%) in the older (3- to 4-year-old and more than 4-year-old) age groups than in the younger cows (10-30%). This study has demonstrated for the first time that if bovine animals susceptible to both A. marginale and BVDV are infected by the two pathogens roughly at the same time, the immunosuppressive effect of BVDV will support the progression of A. marginale infection and manifestation of the disease resulting in acute clinical signs.