Prevalence Of Bovine Leukemia Virus Research Articles

The recent prevalence of bovine leukemia virus (BLV) infection among Japanese cattle

A seroepidemiological survey of bovine leukemia virus (BLV) infection was conducted in Japan in 2007 using an enzyme-linked immunosorbent assay (ELISA) and an agar gel immunodiffusion (AGID) test. A total of 5420 cattle (dairy, 3966; breeding beef, 797; fattening beef, 657) from 209 farms in seven prefectures in Japan were tested. The overall prevalence of BLV infection was 28.6%. The prevalence of BLV infection in dairy cattle (34.7%) was higher than for both fattening beef cattle (7.9%) and breeding beef cattle (16.3%). Age-specific prevalence showed that BLV prevalence increased with age in all types of cattle and was notably different between dairy and beef cattle under 1 year of age. Among 207 farms, 141 herds (68.1%) had one or more positive animals. The proportion of these positive farms was significantly higher among dairy farms (79.1%) than among beef breeding farms (39.5%) and beef fattening farms (51.9%) ( P < 0.001). Dairy farms (40.5%) also showed a significantly higher within-herd prevalence than beef breeding (27.4%) and fattening (14.9%) farms ( P = 0.001). This study indicated that BLV is more widely spread in dairy cattle than in beef breeding cattle in Japan. Given the prevalence of BLV infection in dairy and beef cattle was 8- and 1.7-fold higher, respectively, than rates previously found in 1980–1982, BLV appears to be spreading particularly among the dairy cattle population during the last two decades. Further investigation is required to determine the risk factors necessary to control BLV infection that take into account the different farming practices that exist between dairy and beef sectors.

PREVALÊNCIA DA LEUCOSE ENZOÓTICA EM BOVINOS LEITEIROS CRIADOS NA REGIÃO METROPOLITANA DE CURITIBA – PARANÁ

Enzootic bovine leukosis (EBL) is an infectious, contagious disease caused by bovine leukemia virus (BLV), which is an oncogenic retrovirus of the family Retroviridae. This study evaluates the prevalence of BLV in dairy cattle raised in Curitiba and its surrounding areas. A total of 268 serum samples were collected from five different herds in the municipalities of Sao Jose dos Pinhais, Campina Grande do Sul, Pinhais, and Fazenda Rio Grande. An immunodiffusion (ID) test revealed that 151 (56,34%) animals were positive and 117 (43,66%) were negative.

Effects of subclinical bovine leukemia virus infection on some production parameters in a dairy farm in southern Turkey

Some production parameters of seropositive cows (age, first calving age, 305 day mature equivalent last milk yield production, lifetime mature equivalent milk yield production, lifetime total milk production, lifetime total milking period, lifetime monthly milk production, lifetime daily milk production, lifetime total days of milking, number of inseminations per pregnancy (for last pregnancy), number of calves and calving interval (for last pregnancy)) were analysed in the current study. The study population was clinically healthy Holstein cows from a commercial dairy herd in southern Turkey. Of 109 animals, 65 cows were seropositive by ELISA and the prevalence of bovine leukemia virus (BLV) infection was 59.6%. The prevalence of seropositive cows in 2nd (62.8%), 3rd (64.7%), 4th (61.5%), and 5th (66.6 %) lactations was slightly higher than that of cows in 1st (52.6%) lactations. No statistical differences were observed between BLV seronegative and seropositive cows for production and reproduction parameters analysed in this study (P > 0.05).

Seroprevalence and Field Isolation of Bovine Immunodeficiency Virus.

A seroprevalence study of bovine lentivirus, known as bovine immunodeficiency virus (BIV), was conducted in 12 different dairy herds in Hokkaido, where some herds were a high prevalence of bovine leukemia virus (BLV) infection. Amongst 611 cattle, 28.6% of cattle were BLV-seropositive, and 11.7% of cattle were seropositive for BIV, while 4.2% of cattle were seropositive for both BIV and BLV. For the isolation of BIV, 19 samples of peripheral blood mononuclear cells (PBMC) and one sample of milk-derived leukocytes were prepared from BIV-seropositive cows. These PBMC and leukocyte preparations were then co-cultivated with cc81 cells, a cat cell line transformed by mouse sarcoma virus. BIV was isolated from 17 PBMC and one milk-derived leukocyte samples. The isolated viruses showed slow replication and syncytia formation. Major core antigen, p26 from these isolates were reacted with anti-BIV (American isolate R-29) serum. In addition, proviral DNA was detected in blood and milk samples by nested polymerase chain reaction and subsequent Southern blot hybridization. Nucleotide sequence analysis of the amplified pol gene products showed its 99.0 to 99.7% homology to that of BIV R-29. These results indicate that the Japanese BIV isolates appear to be antigenically and genetically similar to the American R-29. Since BIV was isolated from milk samples, BIV could possibly be transmitted through milk. This is the first report of BIV isolation in Japan.

Evaluation of a bulk-milk ELISA test for the classification of herd-level bovine leukemia virus status

The results of a commercial bulk-milk enzyme-linked immunosorbent assay (ELISA) test for herd-level bovine leukemia virus (BLV) status were compared to results obtained from individual agar-gel immunodiffussion (AGID) testing on sampled cattle. A positive herd was defined as a herd having one or more AGID-positive animals. The estimated true herd status was based on the sensitivity and specificity of the AGID test and the number of cattle sampled per herd. Ninety-seven herds were used, with a mean of 13 cows sampled per herd. The AGID test indicated an apparent herd prevalence of 70.1%. After accounting for the number of cows sampled and the sensitivity and specificity of the AGID test, the estimated true herd prevalence of BLV was 52.3%. The ELISA test identified 79.4% of herds as positive for BLV, and had an apparent sensitivity and specificity of 0.97 and 0.62, respectively. However, after accounting for the sensitivity and specificity of the AGID test in individual animals, the specificity of the ELISA test was 0.44. The ELISA test was useful for identifying BLV-negative herds (i.e., ruling out the presence of BLV infection in test negative herds). With the moderately low specificity, herds identified as positive by the ELISA test would require further testing at the individual or herd level to definitively establish their BLV status.

A path model of factors influencing bovine leukemia virus transmission between cattle herds

A path model was used to investigate the effects of some variables on bovine leukemia virus (BLV) transmission between herds. Data were obtained from 88 outbreaks of BLV infection and 92 herds free from BLV in Catalonia (Spain). The LISREL program was used to carry out the path analysis. This program enables the use of latent variables (they are treated by means of a factorial analysis). The interest and effort devoted to the improvement of farm management is a latent variable and has been quantified through four observable variables (official records of lactation, milk yield, percentage of imported semen, and frequency of reproductive control visits). These four variables explained 73% of the latent variable. Two models were elaborated, allowing explanation of 47 and 69%, of the variation in the presence or absence of the virus in the herd. The introduction of new animals into the herd had a significant effect on the outbreaks of BLV: the risk due to the introduction of positive animals (defined from the number of animals introduced, their age and the prevalence in the sites of origin) had a path coefficient of 0.83. When the variables, number of animals introduced and BLV prevalence in the herd of origin were considered separately, both factors were important: the number of new animals had a coefficient of 0.42, and prevalence in the herd of origin a coefficient of 0.47. The variables associated with possible iatrogenic transmission had negligible effects. The size of the herd had important effects on the presence of BLV (0.34); the model explains this indirect effect through the number of animals introduced into the herd. The hypothesized relationship between improvement of farm management and the leukosis outbreaks seems to be correct (coefficient of 0.17), being an indirect causal relationship through the prevalence in the site of origin of introduced animals.

Detection of bovine leukemia virus antibodies in bulk tank milk using an ELISA test: Improvement of the predictive value of results by repeated testing

In 9457 dairy farms located in an area with low prevalence of bovine leukemia virus (BLV) infection, bulk tank milk was examined to detect for the presence of antibodies using an ELISA test. If the result was positive or doubtful, serum of all animals in the farm was tested and bulk tank milk was tested again five times every 8–12 days. The results were used to establish decision rules in the event of a positive or doubtful result during mass screening.

Transmission of bovine leukemia virus: Prevalence of antibodies in precolostral calves

A study was undertaken to determine the prevalence of bovine leukemia virus (BLV) antibodies in the serum of precolostral calves born to BLV antibody positive dams. Two Michigan dairy herds with breeding programs designed to increase milk production were utilized in this study. The prevalence of seropositive cows was 32% and 94% in herds 1 and 2, respectively, and neither herd had experienced more than four cases of lymphosarcoma in 10 years. One hundred and twenty-five calves and their dams were tested for antibody to BLV by the radioimmunoprecipitation assay utilizing glycoprotein antigen. Three of 79 calves (3.8%) born to seropositive dams were seropositive prior to colostral ingestion. None of 46 calves born to seronegative dams was seropositive at birth. The percentage of calves born to seropositive dams that were seropositive at birth was 4.7% in herd 1 and 3.4% in herd 2. This is a much lower rate of in utero BLV exposure than reported in previous studies utilizing a herd in which cows were bred for susceptibility to lymphosarcoma. Therefore, in herds seeking to reduce the prevalence of BLV seropositive animals, it should be possible to retain calves from seropositive dams in greater numbers than previously expected.