Wystepowanie enzootycznej bialaczki bydla [ebb] w warunkach naturalnego zakazenia stad wirusem parainfluenzy [PI3]

The rate of infection with BLV was assessed in 2053 cattle from 17 farms enzootically infected with PI3. The animals were divided into 6 groups according to their age. The highest percentage (38.0 - 56.7) of the animals in all age groups had HI antibody titers from 1:80 to 1:320; the percentage of animals with the titers between 20 and 40 was 9.8 - 27.7. The HI titers decreased along with the age of the animals. The highest percentage of negative results (24.3 per cent) was noticed in calves aged between 6 months and 2 years. In 3-year-old animals the per cent of negative results was 11.9, in 4-5-year-old - 6.9, in cows 6-12-years-old between 5.6 and 2.2. The percentage of ani­mals whose HI titers ranged from 1:640 to 1:5120 was 7.3 - 50 with a gradual increase with age. The rate of seropositive animals for BLV also increased with the age of the animals and it was 28.3, 39.5, 48.0, 54.7, 61.0, 68.6 in reference to PI3, respectively; in sero-negative groups of the animals the findings were 16.0, 26.2,36.5,48.4, 54.1 and 67.0. The results revealed a close correlation be­tween the number of cattle infected with PI3 and the number of the animals infected with BLV