An Outbreak of Enzootic Bovine Leukosis in Upper Egypt: Clinical,Laboratory and Molecular–Epidemiological Studies

In 1989, 220 Holstein Friesian cattle (212 heifers and eight bulls) were imported from Minnesota, USA, to form a closed dairy herd in Arab El‐Aoumar, Assiut, Upper Egypt. In November 1996, some abnormal signs such as loss of weight, decreased milk yield, external lymphadenopathy and decreased appetite were observed on this farm. Serological screening by enzyme‐linked immunosorbent assay revealed a seroprevalence of antibodies directed against bovine leukaemia virus (BLV) of 37.7% in cattle under 2 years old and of 72.8% in animals more than 2 years old. Diagnosis was confirmed by the detection of BLV proviral DNA using polymerase chain reaction with primers amplifying a fragment of the env gene. Out of 21 tested leucocyte fractions from individual animals, 15 were positive showing a BLV‐specific amplicon of 444 base pairs. Analysis of the amplicons for restriction fragment length polymorphisms and DNA sequencing results allowed the isolates to be typed. Since this was the first recorded case of enzootic bovine leukosis in Upper Egypt, strict quarantine measures were adopted and all serologically positive animals in the herd were culled.     

Bovine leukaemia virus infection in New Zealand cattle

Bovine Leukaemia Virus (BLV) infection in New Zealand cattle was investigated. In a national survey of 5000 sera from 500 herds, BLV antibody was not detected. An additional 1062 sera from 140 herds were tested and 3 sera were positive. In the herd of origin of one of these 3 sera, 22.6% of cattle were serologically positive for BLV. Where cases of bovine lymphosarcoma had been diagnosed, 38 of 39 herds tested were negative for BLV antibody. Within the remaining herd, 36% of cows tested were serologically-positive. BLV was isolated from 2 serologically positive cows in this herd.     

Bovine leukaemia virus infection in New Zealand cattle

Bovine Leukaemia Virus (BLV) infection in New Zealand cattle was investigated. In a national survey of 5000 sera from 500 herds, BLV antibody was not detected. An additional 1062 sera from 140 herds were tested and 3 sera were positive. In the herd of origin of one of these 3 sera, 22.6% of cattle were serologically positive for BLV. Where cases of bovine lymphosarcoma had been diagnosed, 38 of 39 herds tested were negative for BLV antibody. Within the remaining herd, 36% of cows tested were serologically-positive. BLV was isolated from 2 serologically positive cows in this herd.     

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.     

Proviral detection and serology in bovine leukemia virus-exposed normal cattle and cattle with lymphoma.

Twenty-seven cattle with lymphoma and 46 cows from a known bovine leukemia virus (BLV)-infected herd were tested for anti-BLV antibody by the agar gel immunodiffusion (AGID) test and an enzyme-linked immunosorbent assay (ELISA). The polymerase chain reaction (PCR) and Southern hybridization were used to detect BLV provirus in the tumor DNA of the 27 cattle with lymphoma. The PCR was used to detect BLV provirus in the peripheral blood mononuclear cell DNA of the 46 normal known-exposed cattle. Two presumed false negative AGID test results compared to ELISA were found. Of ten cattle three years of age or less with "sporadic" forms of lymphoma, four had BLV provirus in tumor DNA, detectable by PCR. In two of these four, BLV provirus was clonally integrated based on digestion of tumor DNA with restriction enzymes followed by Southern hybridization. The BLV provirus was not detected by PCR in 5 of 17 cattle with "enzootic" lymphoma and two of these five were seronegative. Among normal BLV-exposed cows, 6.5% (3 of 46) were serologically positive and PCR negative; serologically negative and PCR positive cows occurred with the same frequency. Serological and PCR test results, when considered in all cattle (n = 73), had a concordance rate of 83.6%. Discordant test results occurred with approximately equal frequency between serologically positive and PCR negative (7 of 73, 9.6%) and serologically negative and PCR positive (5 of 73, 6.8%) groups. These data suggest that the role of BLV in some "sporadic" bovine lymphomas, previously unassociated with BLV, should be reexamined. The BLV provirus was not demonstrable in the tumor DNA from five adult cattle with lymphoma, suggesting that BLV may not be the etiological agent in all adult bovine lymphomas. The findings of persistently seronegative PCR positive and seropositive PCR negative cattle indicate that further work is needed to more fully understand the host-virus interaction. Present serological screening methods may not have sufficient sensitivity for determining BLV status in some circumstances.     

Risk factor analysis of bovine leukemia virus infection in dairy cattle in Egypt

Identification of the risk factors associated with Enzootic bovine leukosis (EBL) is essential for the adoption of potentially prevention strategies. Accordingly, our objectives were to determine the geographic distribution of Bovine Leukemia Virus (BLV) infection and identify the risk factors associated with cow-level BLV infection in the Egyptian dairy cattle. A cross-sectional study was conducted on 1299 mixed breed cows distributed over four provinces in the Nile Delta of Egypt in 2018. The randomly selected cows on each farm were serologically tested for BLV, and the cow’s information was obtained from the farm records. Four variables (geographic location, herd size, number of parities, and age) were used for risk analysis. A total of 230 serum samples (17.7 %) were serologically positive for BLV. The highest prevalence of BLV infection was associated with parity (OR = 3.4, 95 %CI 2.4–4.9) with 80 % probability of being BLV-positive at parity ≥5, followed by herd size (OR = 1.8, 95 %CI 1.4–2.2). However, geographic location seems to have no impact on the prevalence of BLV infection in Egypt. Our findings strongly indicate that the intensive surveillance and effective prevention strategies against BLV infection in Egypt should be provided to multiparous cows with ≥5 parities and live in large farm with more than 200 cows.     

Serologic and virologic investigations on the presence of BLV infection in a dairy herd in Syria

237 cattle of a dairy herd in Syria were tested for anti-BLV antibody by the ELISA. 194 animals were additionally examined by the agar gel immunodiffusions test (AGID) on BLV antibodies and 100 by polymerase chain reaction (PCR) for BLV provirus. BLV specific antibodies were determined by means of AGID and ELISA at 62.9% and 69.2% of the examined animals, respectively. Using the PCR method the BLV provirus was detected in 89% of the investigated cattle. Only one ELISA seropositive animal was negative for BLV provirus. The results show the high BLV contamination of this herd and lead to the presumption of wide spread enzootic bovine leukosis in Syria. In the case of the diagnosis of BLV-infection, the PCR-technique compared to the serological tests proved to be much more sensitive. By the detection of BLV antibody, the ELISA showed a higher sensitivity than the AGID and in this way, is advisable as a method of choice for screening investigations. Restriction enzyme and sequence analysis of PCR-amplificates demonstrate that different BLV provirus variants (A, B and C) in the examined herd occur, where the variant C which a high similarity to an Australian BLV provirus isolates showed, occurred most frequently at 92.5%.     

Eradication of bovine leukemia virus infection from a high-prevalence herd, using radioimmunoassay for identification of infected animals

Radioimmunoassay (RIA), using the virion glycoprotein antigen, was applied in an attempt to eradicate bovine leukemia virus (BLV) infection from a herd in which virtually all the adult cattle are infected. Considering that most calves born to BLV-infected cows are negative for BLV at birth and remain negative for the first several months of life, the eradication program was based on the identification and isolation of the BLV-free calves born to infected cows. Twenty-five calves raised on colostrum and milk from their infected dams were classified as BLV-free on the basis of negative results in the RIA at 6 to 8 and 9 to 11 months of age. These animals were maintained in either complete (10 calves) or partial (15 calves) isolation from infected cattle and were examined at regular intervals for BLV and BLV antibodies. With the exception of 1 calf in the group raised in partial isolation, the animals have remained free of BLV up to the time of the last evaluation, when they were 32 to 35 months old. At these ages, more than 90% of the nonisolated cattle in the herd are BLV-positive. The data also show that this eradication trial would have failed if, in the initial procedure used to classify the calves as BLV-free, the agar gel immunodiffusion test instead of the RIA had been used. Inasmuch as the 25 calves in this study were fed colostrum and milk from their dams, the fact that only 1 of the calves became infected during the 26 to 29 months of observation provides further evidence that milk-borne transmission of BLV is infrequent and perhaps inconsequential.     

Bovine leukemia virus: A herd-based control strategy

A study was conducted in order to develop a herd-based control strategy for bovine leukemia virus (BLV). Michigan State University's closed lactating dairy herd of 114 cows was utilized for the study. Ninety-five percent (95%) of the cows were positive for BLV antibodies, as determined by the agar gel immunodiffusion (AGID) test in November 1979. To develop the control strategy program, the following management practices were instituted: there was a complete physical separation of BLV positive from BLV negative animals for 3 years after which the two groups were physically mixed. Different and sterile supplies and equipment were utilized for any veterinary-medicine-related activity. Personnel working on the farm were constantly made aware of the transmission of the disease and how to minimize it. A constant vector control program and other miscellaneous management practices were implemented. The BLV seronegative animals were examined monthly for BLV antibodies starting at 6–7 months of age. The reactor animals were separated from the seronegative animals when the reactors had 2 positive AGID tests consecutively. A positive BLV serotest was not a criterion for culling. Following a 3-year complete separation of positive animals from negative animals, the overall point prevalence decreased from 95 to 34%. The results were further categorized according to 4 age groups of 6–15, 16–23, 24–47 and 48 months and older. The percentage of BLV-positive animals decreased from 19 to 17, 58 to 14, 90 to 33 and 100 to 90% for the respective age groups. Following a 10-month discontinuation of physical separation of positive animals from negative animals, a decrease in the overall point prevalence rate was still observed. The limitations and practical applications of the program are discussed.     

Evidence for transmission of bovine leukemia virus by rectal palpation in a commercial dairy herd

The risk of Bovine Leukemia Virus (BLV) transmission by rectal examination was determined over 22 months in a commercial dairy herd. All 167 BLV seronegative cattle, of breeding age or greater, were divided randomly into two groups and identified by neck-chain color. In the treatment group, routine rectal palpation occurred after a BLV infected animal and without a change of sleeve, while in the other group, palpation occurred in a similar manner with the exception that sleeves were changed between animals. When BLV seronegative cattle in either group were palpated after BLV infected cattle, the event and identification of the cattle involved were recorded. Serologic testing was performed eight times during the 22 month study to determine the number of animals that became infected following a palpation (an event). Thirty-one animals seroconverted during the study; 24 in the treatment (no sleeve change) group and seven in the sleeve change group. Sixteen of the animals in the treatment group that seroconverted had been palpated prior to their seroconversion. A hazard ratio (relative risk) for BLV seroconversion was determined between the two groups. Cows palpated with no sleeve change had a 2.8-fold increase in risk (confidence interval 1.1–6.8) of BLV infection. The increased risk of BLV infection associated with rectal palpation may have been affected by the presence of some highly infectious cows in the herd. This study confirms that rectal palpation without a change of sleeve may be a significant risk factor in some herds, and if efforts are made to decrease the spread of BLV in a herd, the potential for rectal sleeve transmission must be considered.     

Survey for antibodies to leukemia (C-type) virus in cattle.

Serums from 4,394 dairy cattle in 100 herds and from 2,794 beef cattle in 50 herds were tested for antibody to the bovine (C-type) leukemia virus (BLV), using the agar gel immunodiffusion test. Reactors were found in 66% of the dairy herds (10.2% of the cattle) and in 14% of the beef herds (1.2% of the cattle). The prevalence of reactors was examined with respect to age, herd size, and sex. Few of the reactors were less than 2 years old. There was a high percentage of reactors in small dairy herds (less than 50 cattle). In 22 dairy herds (1,354 cows and 96 bulls), the rate of infection in cows was compared with that in bulls. In those herds, 13.5% of the cows and 10.4% of the bulls were reactors.     

Detection and molecular characterization of bovine leukemia virus in beef cattle presented for slaughter in Egypt

Bovine leukemia virus (BLV) is the etiological agent of enzootic bovine leukosis, the most common neoplastic disease of cattle worldwide and a serious problem for the cattle industry. Previous studies have shown the molecular prevalence of BLV and the coexistence of BLV genotype-1 and -4 in Egyptian dairy cattle; however, the molecular characteristics of BLV in Egyptian beef cattle are unknown. Therefore, we collected blood samples of 168 beef cattle from slaughterhouses in three governorates in Egypt. Based on BLV-CoCoMo-qPCR-2 targeting long terminal repeats and nested PCR targeting the env-gp51 gene, the BLV provirus infection rates were found to be 47/168 (28.0%) and 42/168 (25.0%), respectively. Phylogenetic analysis based on 501 bp of the BLV env-gp51 gene from 42 BLV isolates revealed that at least six distinctive strains (b, e, f, g, x, and z) were prevalent in cattle across the examined regions. Furthermore, phylogenetic analysis of the 420 bp sequence of the BLV env-gp51 region of the six strains against 11 known genotypes showed that the strains b, e, f, and g were clustered into genotype-1, and strains x and z were clustered into genotype-4. Our results also indicated that strains b and x exist in both dairy and beef cattle in Egypt. The present study is the first to detect and genotype BLV among beef cattle in Egypt.     

Decreased expression of L‐selectin (CD62L) on lymphocytes in enzootic bovine leukaemia

Expression of L‐selectin was determined by single‐ and two‐colour immunofluorescence on granulocytes, peripheral blood mononuclear cells (PBMC) and blasts of bovine origin by means of a monoclonal antibody IVA94 which recognizes bovine L‐selectin (CD62L). Cells were separated from peripheral blood of healthy cattle and colleagues infected with bovine leukaemia virus (BLV). BLV‐infected animals comprised lymphocytotic and non‐lymphocytotic cows. L‐selectin was expressed on 90–98 % of granulocytes in all tested animals. The percentage of PBMC expressing L‐selectin was lower in cattle with persistent lymphocytosis than in non‐lymphocytotic or BLV‐free cattle, and inversely correlated with lymphocyte counts. The ratio of B lymphocytes stained for L‐selectin was significantly decreased from 60.2 ± 1.9 % in BLV‐free cattle to 43.8 ± 3.6 and 22.5 ± 5.7 % in non‐lymphocytotic and lymphocytotic cattle, respectively. B‐lymphocytes stained for L‐selectin exhibited about 50 % reduction in L‐selectin expression in BLV‐infected cattle compared with BLV‐free cattle, as judged by the mean fluorescence intensity (MFI). The percentage of L‐selectin‐positive PBMC not bearing surface immunoglobulin M (predominantly T lymphocytes) was comparable in BLV‐free and BLV‐infected cattle. However, L‐selectin expression on T lymphocytes was reduced (about 50 %) in BLV‐infected cattle, as judged by the MFI. We suppose that BLV infection results in a decreased L‐selectin expression on lymphocytes, and accordingly, it may contribute to deregulation of the host immune system.     

Response of cattle persistently infected with bovine virus diarrhoea virus to bovine leukosis virus

Six cattle persistently infected with bovine virus diarrhoea virus (BVDV) and seronegative, and two control, virus negative seropositive cattle were inoculated with lymphocytes infected with bovine leukosis virus (BLV). The two controls produced a normal immune response to BLV, developing antibodies at four and five weeks after inoculation. Two of the six cattle persistently infected with BVDV developed a strong antibody response by six weeks after inoculation with BLV. Four developed a depressed response to BLV, characterised in three by a 'hooking' reaction in the immunodiffusion test which persisted in successive bleedings but was interspersed occasionally by a weak positive reaction. In one of these animals, a series of 'hooking' reactions was followed by a number of negative results. The fourth animal remained serologically negative until 16 weeks after inoculation when a 'hooking' reaction was observed followed by a series of negative results. BLV was isolated from all the cattle persistently infected with BVDV at 42 or 58 weeks after inoculation regardless of whether the serum samples gave negative, 'hooking', weak positive or positive reactions in the immunodiffusion test. BLV was consistently isolated from the nasal secretions of a steer which was BVDV negative but seropositive. The possibility of decreased immune responsiveness to BLV in animals persistently infected with BVDV should be considered when formulating regulations governing the testing of animals for freedom from BLV.     

Description of the infection status in a Norwegian cattle herd naturally infected by Mycobacterium avium subsp. paratuberculosis

The Norwegian surveillance and control programme for paratuberculosis revealed 8 seroreactors in a single dairy cattle herd that had no clinical signs of Mycobacterium avium subsp. paratuberculosis (M. a. paratuberculosis) infection. Paratuberculosis had been a clinical problem in goats several years previously in this herd. All 45 cattle were culled and a thorough investigation of the infection status was conducted by the use of interferon-gamma (IFN-gamma) immunoassay, measurement of antibodies, and pathological and bacteriological examination. In the IFN-gamma immunoassay, 9 animals gave positive results, and 13 were weakly positive, while 19 animals were negative. In the serological test, 10 animals showed positive reactions, and 5 were doubtful, while 30 animals gave negative reactions. There appeared to be a weak trend toward younger animals having raised IFN-gamma and older animals having raised serological tests. Histopathological lesions compatible with paratuberculosis were diagnosed in 4 animals aged between 4 and 9 years. Three of these animals had positive serological reaction and one animal gave also positive results in the IFN-gamma immunoassay. Infection was confirmed by isolation of M. a. paratuberculosis from 2 of these 4 animals. One single bacterial isolate examined by restriction fragment length polymorphism (RFLP) had the same profile, B-C1, as a strain that had been isolated from a goat at the same farm several years previously. Despite many animals being positive in one or both of the immunological tests, indicative of a heavily infected herd, none of the animals showed clinical signs and only one cow was shown to be shedding bacteria. A cross-reaction with other mycobacteria might have caused some of the immunoreactions in these animals. It is also possible that the Norwegian red cattle breed is resistant to clinical infection with M. a. paratuberculosis.     

Seroprevalence of bovine immunodeficiency virus and bovine leukemia virus in draught animals in Cambodia

Since bovine immunodeficiency virus (BIV), known as bovine lentivirus, has been detected in dairy and beef cattle in various countries around the world, a prevalence study of antibodies to BIV and bovine leukemia virus (BLV) was conducted in draught animals in five provinces in Cambodia, where protozoan parasite infections were suspected in some animals. To clarify the status of draught animals including Haryana, Brahman, mixed-breed, local breed cattle and muscle water buffaloes, a total of 544 cattle and 42 buffaloes were tested, and 26.3 and 16.7%, respectively, were found positive for anti-BIV p26 antibodies determined by Western blotting. There were 5.3% positive for anti-BLV antibodies detected by immunodiffusion test among the cattle, but no reactors among buffaloes and no dual infection for both BIV and BLV was determined in this study. Peripheral blood mononuclear cells from BIV-seropositive cattle were found to have BIV-provirus DNA, as detected by polymerase chain reaction and subsequent Southern blot hybridization. This is the first evidence for the presence of BIV and BLV infections in draught animals in tropical countries such as Cambodia. This wide distribution of BIV suggests its association with problems in animal health as reported worldwide, and that a primary BIV infection can predispose death of affected animals by other aggressive pathogens or stresses.     

Seroprevalence of bovine leukemia virus in dairy cattle in Argentina: comparison of sensitivity and specificity of different detection methods

Bovine leukemia virus (BLV) is a retrovirus that induces a chronic infection in cattle, which develop in three possible pathological forms: asymptomatic course, persistent lymphocytosis (PL) and lymphosarcoma. Once infected, cattle remain virus carriers for life and start to show a serological reaction within a few weeks after infection. Eradication and control of the disease is based on early diagnostic and segregation of the carriers. The agar gel immunodiffusion (AGID) test has been the serological test of choice for routine diagnosis of serum samples. Nevertheless, in more recent years, the enzyme-linked immunosorbent assay (ELISA) has replaced the AGID for large scale testing. Although Argentina has over 60 million cattle population, no nationwide studies have been conducted yet to determine the prevalence of the infection. To estimate the rate of BLV infection in dairy cattle in Argentina, a survey for specific antibodies in >10,000 serum samples from animals over 18 months old, belonging to 363 different herds from the largest dairy production areas of the country, was carried out in our laboratory, along 1999. For this purpose, we developed an ELISA to detect serum antibodies against the BLV virus. The cut-off of the ELISA was established over 339 serum samples, using polymerase chain reaction and southern blot (PCR-SB) as confirmatory test. The sensitivity and specificity of the ELISA was of 97.2 and 97.5%, respectively, while the local official AGID test showed a sensitivity of 79.7% and specificity of 99.0%. To know the seroprevalence of BLV on dairy herds, and also the incidence of the infection within the herd, the serological survey was based on individual serum samples. The results show that the prevalence of infected individuals is of 32.85%, while the percentage of infected herds, harboring one or more infected animals, is of 84%. These results indicate a medium level of seropositive animals when taken individually, but a high prevalence of infected farms, which has been notoriously increased in the last 15 years as shown when compared with previous data from particular geographic areas, indicating that BLV constitutes a serious sanitary problem for dairy producers in Argentina. They also indicate the poor sensitivity of the official AGID test used in the country.     

Seroprevalence of infection with Mycobacterium avium subspecies paratuberculosis, bovine leukemia virus, and bovine viral diarrhea virus in maritime Canada dairy cattle

The purpose of this study was to survey the seroprevalence of infection with the agents of production-limiting diseases in dairy cattle in New Brunswick, Nova Scotia, and Prince Edward Island. In 30 randomly selected herds per province, 30 cattle per herd were randomly selected and tested for antibodies to bovine leukemia virus (BLV) and Mycobacterium avium subspecies paratuberculosis (M. paratuberculosis), while 5 unvaccinated cattle over 6 months of age were tested for antibodies to bovine viral diarrhea virus (BVDV). For BLV, 20.8% (15.8% to 27.0%) of cows were positive, and 70.0% (60.3% to 79.7%) of herds had at least one positive cow. In BLV-positive herds, the average BLV prevalence was 30.9% (24.8% to 37.2%). For M. paratuberculosis, 2.6% (1.8% to 3.9%) of cows were positive, and 16.7% (8.8% to 24.5%) of herds had at least 2 M. paratuberculosis-positive cows. In M. paratuberculosis-positive herds, the average M. paratuberculosis prevalence was 8.5% (6.9% to 10.1%). For BVDV, 46.1% (35.5% to 56.7%) of herds had at least 1 BVDV-positive animal with a titer greater than or equal to 1:64.     

Molecular studies of T-lymphocytes from cattle infected with bovine leukemia virus

Although bovine leukemia virus (BLV) is mainly associated with infections of B-lymphocytes, we have previously reported the statistically significant increase in the T-lymphocytes obtained from BLV-infected asymptomatic aleukemic (AL) cattle. In this report the presence of BLV provirus in the DNA of immunoaffinity purified T-lymphocytes from AL animals was assessed using a highly specific radiolabelled (32P) BLV-DNA provirus probe and solid phase DNA hybridization. The BLV provirus was found in the DNA of the peripheral blood mononuclear cells of all AL animals tested and three of the four purified T-lymphocyte preparations from these animals. The purified T-lymphocyte preparations used in this study contained less than 4% detectable B-lymphocytes. One animal had no detectable B-lymphocytes in the purified T-lymphocyte preparation and the DNA from these cells also gave positive hybridization results. The lymphocyte blastogenesis assay was then used as an indicator of the functional ability of lymphocytes from these BLV-infected AL cattle to respond to mitogenic stimuli. The responsiveness of lymphocytes from these animals to the mitogens concanavalin A (Con A), phytohemagglutinin (PHA), and pokeweek mitogen (PWM) was comparable to that of lymphocytes from BLV-negative animals when changes in 3H-thymidine uptake (c.p.m.) were used as measurement of mitogenic-induced blastogenesis. This indicated that infection of the T-lymphocytes by BLV does not appear to alter the overall response of the lymphocyte populations to mitogenic stimuli. High levels of spontaneous blastogenesis in the absence of mitogenic stimulation were observed for lymphocyte preparations of AL animals. The reason for this proliferation of lymphocytes is unclear; however, sera from these AL animals were found to contain a blastogenesis-augmenting factor(s) when added to lymphocytes from BLV-negative control animals in the presence of Con A, PHA and PWM.     

Seroprevalence and molecular evidence for the presence of bovine immunodeficiency virus in Brazilian cattle

Data on the worldwide distribution of bovine immunodeficiency virus (BIV) and bovine leukemia virus (BLV) is limited. A prevalence study of antibodies to BIV and BLV was conducted in six different cattle herds in Brazil. Out of a total of 238 sera analyzed, 11.7% were found positive for anti-BIV p26 antibodies as determined by Western blot analysis, 2.1% were positive for anti-BLV gp51 antibodies as detected by immunodiffusion test. Peripheral blood mononuclear cells from BIV seropositive cattle were found to have BIV-provirus DNA, as detected by nested polymerase chain reaction. A nucleotide sequence corresponding to a 298 bp fragment of the BIV pol gene was also analyzed. Amino acid sequences of these Brazilian pol gene products showed 98.0 to 100% homology to the American strain BIV R29, 97.0 to 99.0% to Japanese BIV isolates, and divergence ranged from 0 to 4.0% among Brazilian BIV isolates. This evidence of the presence of BIV and BLV infections in Brazil should be considered a health risk to Brazilian cattle populations and a potential causative agent of chronic disease in cattle.