Ocorrência de animais persistentemente infectados pelo vírus da diarréia viral bovina em rebanhos bovinos nos Estados de Minas Gerais e São Paulo

Abstract

A pesquisa de animais persistentemente infectados (PI) pelo vírus da diarréia viral bovina (BVDV) foi realizada em 26 rebanhos bovinos, não vacinados contra o BVDV, localizados nos Estados de Minas Gerais e São Paulo, Brasil. Utilizando uma estratégia de amostragem, de cada rebanho foram obtidas cinco amostras de sangue de bezerros, entre 6 e 12 meses de idade, e os soros sanguíneos foram submetidos ao teste de virusneutralização (VN) para o BVDV-1 e o BVDV-2. Os rebanhos que apresentaram pelo menos três das cinco amostras reagentes a um dos genótipos do BVDV, e com títulos de anticorpos superiores a 128, foram selecionados para a pesquisa de animais PI. Em três rebanhos que apresentaram tal condição, foram colhidas amostras pareadas de sangue de todos os bovinos do rebanho, com intervalo de 30 dias entre as colheitas, e o soro sanguíneo foi submetido ao teste de VN para o BVDV-1 e o BVDV-2. Nas amostras não reagentes a pelo menos um dos genótipos do BVDV e naquelas provenientes de bovinos com menos de seis meses de idade, realizou-se a pesquisa do BVDV pela reação em cadeia da polimerase precedida pela transcrição reversa (RT-PCR). Dos rebanhos analisados, foram detectados dois animais PI a partir de amostras obtidas nas colheitas pareadas provenientes de um rebanho localizado no Estado de Minas Gerais.

Prevalence of bovine brucellosis, paratuberculosis, enzootic leucosis, and antigen-reactive agents to bovine viral diarrhea virus in animals up to one year old

“…Brazilian studies of BVD typically analyze the detection of antibodies against BVD virus, meaning that seropositive animals may have presented negative results in the ELISA test used in this study. Although Dias et al (2010) conducted a serological screening to detect antibodies against BVD virus in animals from six to 12 months of age from 26 herds in SP and MG, they could only identify two persistently infected (PI) animals using a polymerase chain reaction technique preceded by reverse transcription (RT-PCR), which makes further comparisons between that study and the present one difficult due to the different methods used. However, more studies on BVD, with larger samples and in different Brazilian states, are greatly needed, since BVD may represent an obstacle for live cattle export by the country.…”

“…There is little data in the literature on bovine PTB serological surveys in Brazil, and the present study was the first in Brazil to conduct a serological survey of PTB in the states of GO, MG, and SP. PTB is diagnosed more frequently in dairy cattle than in beef cattle due to the longer exposure of dairy animals to sources of infection, such as chronically infected adult animals, contaminated pastures, and other elements that may carry MAP and be used as transmission agents, thus increasing the infection rates and prevalence of this disease (FISS et al, 2015;ROSSI et al, 2017). This may be the reason for the low occurrence of this disease in the present study, in which only 5.33 and 5.50% of the sera from young male cattle from eight to 12 months of age were seropositive for PTB.…”

“…Previous studies conducted PTB serodiagnoses in other Brazilian states, and found that the occurrence of seropositive animals aged 24 months or older was 34.5% (864/2,504) in Paraíba (VILAR et al, 2015) and to identify risk factors associated with herd-level prevalence for bovine paratuberculosis in the State of Para\u00edba, Northeastern Brazil. The state was divided into three sampling groups: sampling stratum 1 (mesoregion of Sert\u00e3o, 2.7% (11/408) in Pernambuco (SÁ et al, 2013), 14.7% (5/34) in in Rio Grande do Sul (FISS et al, 2015), and 13.2% (165/1,450) in Espírito Santo (COSTA et al, 2010). Compared to the abovementioned results, those of the present study showed a relatively lower prevalence of seropositive animals, although these are results for populations that differed in terms of both their gender and age.…”

Vertical transmissibility of small ruminant lentivirus

“…As for the newborn animals, the reduced number of seropositive individuals by the WB can be attributed to a possible fetal immunotolerance, that is, the virus may have infected the animals before the development of immunological competence, possibly resulting in the generation of animals that present persistent viral infection, without detectable immune stimulus, since the response of the antibodies produced to the viral protein limits, in this case, the test's effectiveness [42,43]. If infection of the fetus occurs when the immune system is immature, viral proteins are mistakenly recognized as belonging to the individual (self), which makes the animal immunologically tolerant.…”

“…Sequencing is a valuable tool for evidencing similarities in strains and has even been used to confirm interspecific transmission of the virus among small ruminants [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49]. But, although nPCR DNA detection occurred in all nine samples and their respective replicates subjected to sequencing, it is believed that the concentration of pro-viral DNA was not adequate for the viable sequencing of all replicates.…”