Postnatal and prenatal transmission of the bovine leukemia virus under natural conditions
Piper, C.E.; Ferrer, J.F.; Abt, D.A.; Marshak, R.R.
Journal of the National Cancer Institute 62(1): 165-168
1979
ISSN/ISBN: 0027-8874 PMID: 214609 Document Number: 139969
Cattle in a well-characterized multiple-case leukemia herd (herd BF) were examined for bovine leukemia virus (BLV) infection and BLV antibodies from birth to adulthood. According to standard husbandry practices for dairy herds, the BF calves were separated from the adult herd after they were weaned up to the ages of 14-16 mo. After the age of 30 mo. all cattle in the herd were infected with BLV and had antiviral antibodies. Only 18% of the BF calves were positive at birth and before their 1st colostral meal. Thus prenatal transmission of BLV was relatively infrequent. Several observations indicated that prenatal transmission occurred only through the placenta. After ingestion of colostrum and for the first 3-5 mo. of life, all the BF calves had passively acquired maternal antibodies to BLV. During this time and until the ages of 7-10 mo., the incidence of BLV infection among the BF calves did not change significantly. Subsequently, the incidence increased rapidly, and when the calves reached 2 yr of age, it was 93%. BLV infection was detected in only 3 of 17 BF calves of similar ages that were virus-free at birth and kept in isolation after weaning from their BLV-infected dams. Apparently the large majority of the BF cattle were infected with BLV by contact following exposure to the adult herd and, during the 1st weeks of life, they were protected against milk-borne or contact infection by passively acquired maternal antibodies. BLV infection in cattle persisted despite the presence of actively produced or passively acquired BLV-neutralizing antibodies.