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.     

Comparison of the agar gel immunodiffusion test and ELISA in the detection of bovine leukosis virus antibody in cattle persistently infected with bovine virus diarrhoea virus

When six cattle persistently infected with bovine virus diarrhoea virus (BVDV) were inoculated with lymphocytes infected with bovine leukosis virus (BLV), a depressed antibody response to BLV was observed by ELISA which was due to a decrease in IgG1 synthesis. The ELISA was more sensitive and more reliable than the agar gel immunodiffusion (AGID) test in detecting BLV infection in cattle persistently infected with BVDV. Decreased antibody responses were manifested in the AGID test by negative, inconclusive or weakly positive reactions: only two of the six cattle developed antibodies that generated positive AGID reactions.     

Experimental and natural infection with the enzootic leukosis virus of cattle

A trial was performed with heifers at the age of six to seven months. The animals were experimentally infected with the lymphocytes of a virus-productive donor. Infection was produced in all the nine cases, as demonstrated by means of the positive syncytial test. As indicated by the results of the trial, the antibodies to the enzootic bovine leucosis virus (BLV) were produced soon after experimental infection. A high sensitivity of the serum-neutralization test and the ELISA method was demonstrated in this connection: by these methods, the antibodies were identified already two to three weeks after experimental infection whereas by the immunodiffusion test they could be detected only after five weeks. Twenty-four animals were exposed to natural contact infection. Within 270 days of the trial, the disease after contact was recorded only in one heifer out of the four that were in close contact with the experimentally infected animals. In this case, as compared with experimental infection, the antibodies were produced much later--after 85 to 93 days. Leucosis was recorded in none of the remaining animals. The reasons why such a favourable result was obtained were the thorough disinfection of the stables after blood collections and the strict observance of the aseptic conditions. The results of experimental infection in three cows were identical with those obtained in young cattle. In the experimentally infected dairy cows, antibodies in milk were determined by the ELISA method. As found, in milk the antibodies to BLV appear two to three weeks later than they do in serum. The ELISA method of BLV antibody detection can be used for the identification of infected animals in herds where enzootic bovine leucosis occurs.     

The fat content of milk from dairy cattle infected with bovine leukosis virus

Two groups of cows infected with the bovine leukosis virus (BLV) were kept on two different diets and the fat content of their milk was assayed. The results were compared with those obtained from two comparable groups of BLV-free cows. The cows in each group were of similar ages, those in the groups on the poorer diet being 1–4 months post partum, while those on the richer diet were 5–7 months post partum. The mean percentage of fat in the milk from uninfected cows on the poorer diet was 2.94 while that from the similar infected cattle was 3.06. Uninfected cows on the richer diet produced milk containing 3.39% fat, while those that were infected produced milk containing 3.30% fat. No statistical differences in milk fat production were observed between the BLV seropositive and seronegative cows.     

Factors affecting the infectivity of lymphocytes from cattle with bovine leukosis virus.

Peripheral blood mononuclear cells were obtained from 13 bovine leukosis virus infected cattle and inoculated subcutaneously into 29 recipient adult steers to determine (a) the number of mononuclear cells (equivalent amount of blood) necessary to cause infection and (b) factors influencing infectivity of mononuclear cells from bovine leukosis virus-infected animals. A total of 55 inoculations were made. Inoculation of 1 X 10(4), 2 X 10(4) and 5 X 10(4) mononuclear cells caused seroconversion in 12%, 57% and 62% of steers, respectively. No infections occurred with 1 X 10(3) or 2 X 10(3) mononuclear cells. Cattle infected for longer than 24 months and those animals greater than three years of age were more likely to cause infection with 1 to 5 X 10(4) mononuclear cells than were cattle infected for less than 24 months or animals less than three years of age. Lymphocytes from cattle with persistent lymphocytosis caused more infections when 1 X 10(4) or 2 X 10(4) mononuclear cells were inoculated, than did lymphocytes from nonpersistent lymphocytosis cattle; however, both groups were equally infectious when 5 X 10(4) mononuclear cells were inoculated. No differences were found in infectivity of experimentally vs naturally exposed animals.     

Protection against bovine leukosis virus infection in sheep with the BL 20 bovine lymphoblastoid cell line

The bovine lymphoblastoid BL 20 cell line derived from a case of sporadic bovine leukosis when inoculated into sheep did not induce an antibody response directed against bovine leukosis virus (BLV) structural proteins. Sheep were inoculated twice with the BL 20 cell line and then challenged with BLV infected lymphocytes. Three out of four sheep challenged four weeks after BL 20 inoculation did not develop BLV antibodies. Of the 12 sheep challenged later, three sheep did not develop BLV antibodies. BLV was isolated from all the seropositive animals and from none of the seronegative animals.     

Enzootic bovine leukosis virus in Brazil

Summary A sero-epidemiological survey for antibodies to the glycoprotein of enzootic bovine leukosis virus showed that the infection is widely disseminated in the State of Rio de Janeiro, Brazil. Sera from 1,290 females and 154 males from 12 dairy herds were tested by the agar gel precipitin test. Seven hundred and one females (54.3%) and 68 males (44.2%) were found to have specific antibodies. These antibodies were demonstrated in all 7 age groups tested. The older age groups contained the highest percentage of reactors. The results are briefly discussed in relation to management practices and environmental conditions.

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El Virus De La Leucosis Bovina Enzootica En Brasil

Resumen Una encuesta suero-epidemiológica por anticuerpos contra la glicoproteina del virus de la leucosis bovina enzootica mostró que la infección está ampliamente diseminada en el Estado de Rio de Janeiro, Brasil. Sueros de 1290 hembras y 154 machos pertenecientes a 12 rebaños lecheros fueron examinados en la prueba de precipitación en agar. Se encontró que 701 hembras (54.3 por ciento) y 68 machos (44.2 por ciento) poseían anticuerpos específicos. Estos anticuerpos fueron demonstrados en todos los siete grupos de edad examinados. Los grupos de mas edad contenian un porcentaje mayor de reactores. Los resultados son discutidos brevemente en relación a las prácticas de manejo y a las condiciones ambientales locales.

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Virus De La Leucose Bovine Enzootique Au Bresil

Résumé Une enquête séro-épidémiologique pour la détection de la présence de la glycoproteine du virus de la leucose enzootique bovine a montré que cette affection est largement disséminée dans l'Etat de Rio de Janeiro, au Brésil. Des échantillons de sérum provenant de 1290 femelles et 154 mâles appartenant à 12 troupeaux laitiers ont été étudiés par précipitation en gélose—701 femelles (54,3 p. 100) et 68 mâles (44,2 p. 100) ont été reconnus comme possédant des anticorps spécifiques. Ces anticorps ont été mis en évidence dans la totalité des 7 groupes d'âges étudiés. Les groupes d'âges plus élevés contenaient le plus haut pourcentage d'animaux positifs. Les résultats sont brièvement discutés, dans leur relation avec les pratiques de l'élevage et les conditions de l'environnement.

     

Enzootic bovine leukosis virus in Brazil

A sero-epidemiological survey for antibodies to the glycoprotein of enzootic bovine leukosis virus showed that the infection is widely disseminated in the State of Rio de Janeiro, Brazil. Sero from 1,290 females and 154 males from 12 dairy herds were tested by the agar gel precipitin test. Seven hundred and one females (54.3%) and 68 males (44.2%) were found to have specific antibodies. These antibodies were demonstrated in all 7 age groups tested. The older age groups contained the highest percentage of reactors. The results are briefly discussed in relation to management practices and environmental conditions.     

Induction of neutralizing antibodies against bovine leukosis virus in rabbits by vaccination with recombinant vaccinia virus expressing bovine leukosis virus envelope glycoprotein

Three kinds of recombinant vaccinia virus (RVV)--mO-HA/ATI, LO1-HA/ATI and mO-HA/7.5kD--expressing bovine leukosis virus (BLV) envelope glycoprotein (gp60) were constructed. The BLV envelope gene of RVV mO-HA/ATI and LO1-HA/ATI or of RVV mO-HA/7.5kD was expressed under control of the promoter of A-type inclusion body (ATI) protein gene of cow-pox virus or vaccinia virus 7.5-kD protein gene, respectively. The vaccinia virus strain, LC16mO, was used as vector for RVV mO-HA/ATI and mO-HA/7.5kD, and strain LO-1 was used for RVV LO1-HA/ATI. Strains LC16mO and LO-1 are attenuated vaccine virus strains originating from the Lister original vaccinia virus. All 3 kinds of constructed RVV expressed gp60 in cultured rabbit kidney cells after infection; mO-HA/ATI expressed more antigen than did mO-HA/7.5kD. Rabbits vaccinated with RVV produced considerable antibody capable of inhibiting syncytium formation, as well as antibody with virion-binding ability. The RVV that used ATI promoter induced higher antibody titer than did the RVV that used 7.5-kD promoter. Results indicate that BLV gp60 is responsible for induction of neutralizing antibodies that suppress in vitro formation of syncytia among BLV-infected cells. Applicability of RVV, especially those using ATI promoter, was evaluated in a vaccine against bovine leukosis.     

Use of a polymerase chain reaction assay to detect bovine leukosis virus in dairy cattle

OBJECTIVE: To evaluate the use of a polymerase chain reaction (PCR) assay in detecting bovine leukosis virus (BLV) in adult dairy cows. DESIGN: Prospective study. ANIMALS: 223 adult dairy cows. PROCEDURE: Cows were tested for BLV status by use of an ELISA and a PCR assay. Sensitivity, specificity, predictive values of positive and negative tests, and the percentage of cows correctly classified by PCR assay were calculated. Ninety-five percent confidence intervals were calculated for sensitivity and specificity. RESULTS: Sensitivity and specificity were 0.672 and 1.00, respectively. Prevalence of BLV in this herd was 0.807. Predictive value of a positive test was 1.00, and predictive value of a negative test was 0.421. The percentage of cows correctly classified by PCR assay was 73.5%. CONCLUSIONS AND CLINICAL RELEVANCE: A positive PCR assay result provided definitive evidence that a cow was infected with BLV. Sensitivity and negative predictive value for PCR assay were low. Consequently, PCR assay alone is unreliable for routine detection of BLV in herds with high prevalence of the disease.     

Immunology of bovine respiratory syncytial virus infection of cattle

Bovine respiratory syncytial virus (BRSV) is a respiratory pathogen of cattle that causes severe disease in calves alone and as one of several viruses and bacteria that cause bovine respiratory disease complex. Like human RSV this virus modulates the immune response to avoid stimulation of a vibrant CD8+ T cytotoxic cell response and instead promotes a Th2 response. The Th2 skew sometimes results in the production of IgE antibodies and depresses production of the Th1 cytokine interferon γ. Innate immune cells have a pivotal role in guiding the adaptive response to BRSV, with selective secretion of cytokines by pulmonary dendritic cells. Here we review some of the pertinent observations on immune responses to BRSV infection and vaccination and illustrate how experimental infection models have been used to elucidate the immunopathogenesis of BRSV infection. Recent experiments using intranasal vaccination and/or immune modulation with DNA based adjuvants show promise for effective vaccination by the stimulation of Th1 T cell responses.