The Infection Hazard of Carriers of Proviral Bovine Leukemia Virus and Its Evaluation With Regard to Leukocytosis

Abstract

A b s t r a c tThe spread of the bovine leukemia virus (BLV) brings significant economic damage to dairy and beef cattle still due to the problems to develop the optimal methods for its prevention. The situation is compounded by the fact that the clinical manifestation of lymphocytic leukemia has been observed in animals during 5 to 10 years after infection in approximately 5-7 % of animals. Subdivision of BLV infected B cells on the producers of mature viral particles and precursors of the formation of lymphomas necessitates of separately consideration of the risk of infecting animals and forecast for development of lymphocytic leukemia. Testing antibodies to viral antigens, or provirus DNA insertion into the host genomes does not allow to reveal the most dangerous animals in view of their role in the infection spread, which is most essential for its control. In this regard, the particular urgency is the method development to assess the infection hazard from carriers of provirus DNA of bovine leukemia virus, associated with a large number of B lymphocytes, producing mature viral particles. In order to evaluate the possibility of using in these purposes not only testing individual animals on the quantity of viral RNA in blood samples, but the proliferative activity of leucocytes, these two characteristics were compared in the present work. The presence or absence of genome integrated provirus DNA in Black-and-White Holstein cows (n = 57, commercial herd) was evaluated and the group of infected animals was revealed when using primers designed by us for BLV gag and pol genes (G.Yu. Kosovoskii et al., 2013). The relative quantity expression of provirus in individual infected cows using RT-PCR analysis and primers to the fragment of the BLV pol gene were assessed. The counting of leukocytes in blood samples of all cows, included in the analysis, was performed. The number of leucocytes in cows free from infection, with the exception of one cow, was less than 1210 9 cells/l. This indicator in infected animals divided the investigated cows into two subgroupsin the first subgroup the leucocyte values did not exceed 1710 9 cells/l, in the second subgroup the number of leukocytes was significantly higher, reaching 2810 9 cells/l in some animals. It was important to note, that the amount (above 2010 9 cells/l) of BLV RNA, sufficient to detect by RT-PCR, was revealed only in the second subgroup. The coincidence of the increased leucocyte amount and the BLV RNA in blood of infected animals indicates that particular these cows represent the greatest infection hazard and suggests that the combination of estimates of the number of leukocytes and RNA BLV can be quite a reliable approach for the herd recovery by priority of their liquidation.

Bovine leukemia virus pre-miRNA genes’ polymorphism

“…The dividing of BLV-infected animals into two subgroups by WBC values had been noted also in the previous article [35]. The I-st BLV+ subgroup has relatively low WBC counts and the IInd BLV+ subgroup has relatively high WBC counts.…”

“…26 samples from the proviral BLV-negative and the BLV-seronegative group of cows have been taken as the control group (further: BLV-negative or BLV-group). All peripheral blood samples and its WBC counts have been the same as in the previous article [35].…”

Bovine leukemia virus tax gene/Tax protein polymorphism and its relation to Enzootic Bovine Leukosis

“…In this study we have been investigating tax gene and Tax protein polymorphism, and its association with WBC counts. For this purpose, we have been used DNA from 42 peripheral blood samples of 2 to 5 years old female Holstein cattle (farming in Moscow region, Russia), all of which are the same as in previous works [9,18]. WBCs of the samples have been counted on an Abacus Junior Vet 5 Automatic Hematology Analyzer (Diatron, Austria).…”

“…These antibody detection methods, PCR detection of BLV proviral DNA, and BLV virus isolation are recommended to apply on the same clinical samples [5,8]. However, it should be noted, all of those methods reflect only the fact of a contact of an individual animal with the virus, but they do not allow predicting the spread of BLV infection to other susceptible cattle or development of tumors [18].…”

CELLULAR AND EXTRACELLULAR LEVELS OF RETROVIRUS—HOST INTERACTIONS ON THE EXAMPLE OF THE BOVINE LEUKOSE VI-RUS. 2. CRITICAL STAGES — MULTIPLICITY AND VERSATILITY (review)

“…Такой подход высокозатратен и, кроме того, приводит к снижению продуктивного потенциала поголовья, поскольку относительно повышенная чувствительность к инфицированию BLV часто ассоциирована с высокой молочной продуктивностью. Сочетание двух обстоятельств (низкая частота развития собственно лейкоза у инфицированных животных и утрата части высокопродуктивного генофонда при применяемом оздоровлении стад) актуализирует вопросы прогноза индивидуальных рисков онкогенеза и инфекционной опасности носителей BLV (2). В этой связи особое значение приобретает изучение молекулярных механизмов процессов, происходящих на каждом из трех перечисленных выше этапов патогенеза, индуцируемого BLV.…”