EXPERIMENTAL-INFECTION WITH BABESIA DIVERGENS IN CATTLE PERSISTENTLY INFECTED WITH BOVINE VIRUS DIARRHEA VIRUS

Nine Norwegian Red cattle, aged 7-14 months, persistently infected wit h bovine virus diarrhoea virus (BVDV) were inoculated with a Swedish s train of Babesia divergens. Six persistently infected cattle of the sa me age and breed were kept as controls. Blood and serum samples were c ollected regularly during the observation period. Rectal temperatures were recorded every morning for 25 days post infection, and the animal s were examined clinically on a daily basis. Sera were examined for an tibodies to B. divergens by indirect immunofluorescence antibody test (IFAT). Eight of the infected animals developed fever of 2-5 days dura tion. Babesia divergens organisms appeared in the erythrocytes of all infected animals on the day after inoculation. The parasitaemia lasted for 4-11 days. One animal had a transient haemoglobinuria. Compared w ith the control group, there was a 20% decrease in the haematocrit. Th ere was a transient Iymphopenia and thrombocytopenia during the period of fever. There were no differences in mean numbers of neutrophils be tween the two persistently infected groups. Compared with cattle free of BVDV, the persistently infected cattle had consistently lower total leucocyte count that was mainly due to decreased mean numbers of neut rophils and monocytes. Ail infected animals developed antibodies great er than or equal to 1 :1280 between day 7 and 10 post infection. The m agnitude of the antibody response was considerably lower than that of BVDV-free animals inoculated with the same strain and dosage of B. div ergens.