Bovine leukemia virus is an oncogenic retrovirus of the human T-cell lymphotropic virus/BLV group.1 Approximately 44% of dairy cattle and 10% of beef cattle in the United States are infected with BLV.2,3 Cattle infected with BLV mount immune responses to both the viral surface and core antigens. Consequently, serologic tests for BLV performed on calves that ingest colostrum from BLV-infected cows will yield positive results, regardless of the infection status of the calves. Results of a previous study4 indicate that these positive serologic assay results may persist for as long as 6 months.
Transmission of BLV in the perinatal period can occur in utero or through the ingestion of infected colostrum.5–8 Among bovids, in utero infection of fetuses and infection of neonates via colostrum ingestion have been investigated and transmission is estimated to be 3% to 18% and 12%, respectively.5–9 Infection of off-spring during parturition has been postulated to occur but has not been investigated in depth.10,11 In a recent study,10 the transmission rate in colostrum-deprived calves born to BLV-infected cows was 33%; in a control group of colostrum-fed calves born to BLV-infected dams, transmission rate was 0%. It was postulated that exposure to the virus in the colostrum-deprived group occurred at parturition. Thurmond11 postulated that exposure to maternal blood was a normal and expected event during parturition; however, the source of these parturition-associated infections has not been conclusively determined.
Blood inoculation of naïve calves via ID, IV, IM, and SC routes efficiently transmits BLV.12 Seroconversion after blood inoculation can occur as early as 3 weeks and as late as 14 weeks.12 One study13 revealed that detection of seroconversion via AGID lags behind PCR identification of provirus by 2 to 4 weeks. In another study14 of BLV-inoculated calves, the AGID assessment, ELISA, and PCR assay were compared; detection of provirus via PCR assay occurred from day 7 to day 56 after inoculation (depending on challenge dose), and all test results for 3 animals remained negative throughout the study. Seroconversion lagged behind PCR-detected conversion of BLV status in all calves; however, data were not presented to determine whether the timing was similar for all calves. Most studies that compare serologic findings and PCR detection of BLV infection use an AGID assay as the serologic test comparison. The purpose of the study reported here was to compare the interval to provirus and antibody detection (via PCR assay and ELISA, respectively) in calves after experimental inoculation with BLV. We hypothesized that PCR-detected conversion of BLV status would precede seroconversion.
Bovine leukemia virus
Agar gel immunodiffusion
Erythrocyte lysis buffer, Qiagen Inc, Valencia, Calif
QIAamp DNA mini kit, Qiagen Inc, Valencia, Calif
Bovine leukemia virus antibody test kit, ELISA, VMRD Inc, Pullman, Wash
Multiskan RC, MTX Lab Systems Inc, Vienna, Va
HotStarTaq, Qiagen Inc, Valencia, Calif
Perkin-Elmer 9700, Perkin-Elmer Inc, Shelton, Conn.
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National Animal Health Monitoring System. High prevalence of BLV in US dairy herds. Fort Collins, Colo: USDA:APHIS:VS:NAHMS, 1997;Publication N228.197.
National Animal Health Monitoring System. Bovine leukosis virus (BLV) in US beef cattle. Fort Collins, Colo: USDA:APHIS:VS:NAHMS, 1999;Publication N299.299.
Burridge MJ, Thurmond MC, Miller JM, et al. Duration of olostral antibodies to bovine leukemia virus by two serologic tests. Am J Vet Res 1982;43:1866–1867.
Thurmond MC, Carter RL, Puhr DM, et al. An epidemiological study of natural in utero infection with bovine leukemia virus. Can J Comp Med 1983;47:316–319.
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Jacobsen KL, Bull RW, Miller JM, et al. Transmission of bovine leukemia virus: prevalence of antibodies in precolostral calves. Prev Vet Med 1983;1:265–272.
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Nagy DW, Tyler JW, Kleiboeker SB. Enhanced periparturient transmission of bovine leukosis virus in colostrum deprived calves. J Vet Intern Med 2006;20:724–725.
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Kelly EJ, Jackson MK, Marsolais G, et al. Early detection of bovine leukemia virus in cattle by use of the polymerase chain reaction. Am J Vet Res 1993;54:205–209.
Klintevall K, Ballagi-Pordány A, Näslund K, et al. Bovine leukemia virus: rapid detection of proviral DNA by nested PCR in blood and organs of experimentally infected calves. Vet Microbiol 1994;42:191–204.
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Nagy DW, Tyler JW, Kleiboeker SB, et al. Use of a polymerase chain reaction assay to detect bovine leukosis virus infection in dairy cattle. J Am Vet Med Assoc 2003;222:983–985.