Evolution of Specific Antibodies and Proviral DNA in Milk of Small Ruminants Infected by Small Ruminant Lentivirus

Abstract

The diagnosis of Small Ruminant Lentivirus (SRLV) is based on clinical signs, pathological lesions and laboratory testing. No standard reference test for the diagnosis of maedi visna has been validated up to the present, and it is puzzling that tests which detect antibodies against the virus and tests which detect the proviral genome may render opposite results. The aim of this study was to evaluate the presence in milk throughout a lactation period of specific antibodies by ELISA and of SRLV proviral DNA by a PCR of the highly conserved pol region. A six-month study was conducted with the milk of 28 ewes and 31 goats intensively reared. The percentage of animals with antibodies against SRLV increased throughout the study period. Seroprevalence in sheep was 28% at the beginning of the study and by the end it had increased up to 52.4%. In goats, initial seroprevalence of 5.6% increased to 16%. The percentage of PCR positive ewes was stable throughout the study period. Of the positive sheep, 21.4% were PCR-positive before antibodies could be detected and most of them became PCR-negative shortly after the first detection of antibodies. This might suggest that antibodies have a neutralizing effect. In addition, an equal percentage of sheep were always PCR-negative but either became ELISA-positive or was always ELISA-positive, which might support this hypothesis. On the other hand, the PCR results in goats did not follow any pattern and oscillated between 35.3% and 55.6% depending on the month. Most goats positive by PCR failed to develop antibodies in the 6 months tested. We may conclude that the infection and the antibody response to it follow a different trend in sheep and goats.

Transmission of caprine arthritis encephalitis virus between sheep

“…The modification observed for animal 52 may be a mutation (BARQUERO et al, 2013); however, additional detailed studies are needed to confirm this hypothesis, mainly because lamb 54 did not manifest this. The low similarity with strain MVV-K1514 indicated the differences between the sequences reported in the lambs compared to the ovine lentivirus.…”

“…The lack of viral replication reduces the ability to detect its genetic material in tissues (BARQUERO et al, 2013). In addition, the detection capability of the serological techniques is directly related to the level of viral replication that can generate a humoral immune response (TORRES et al, 2009).…”

“…In addition, the detection capability of the serological techniques is directly related to the level of viral replication that can generate a humoral immune response (TORRES et al, 2009). This diagnostic limitation may be reduced by combining different methods (BARQUERO et al 2013); however, viral intermittence must be considered (RAVAZZOLO et al, 2006;RACHID et al, 2013).…”

Transmissibilidade de Lentivírus de Pequenos Ruminantes para cabritos e cabras adultas por meio de sêmen infectado experimentalmente

“…Há hipótese de que os primers não anelariam corretamente com o DNA extraído na técnica, enquanto outra afirma que a alta taxa de mutação destes vírus (1 mutação para cada 10 5 nucleotídeos) seria responsável pela diminuição da eficácia da técnica de PCR para detecção do DNA pró-viral (Barquero et al 2013b). O teste de IDGA nas fêmeas adultas detectou maior número de animais infectados em relação ao nested-PCR, pelo qual nenhum positivo fora detectado.…”

“…O DNA pró-viral está apenas nestas células, implicado na falha da detecção simplesmente pela carga viral abaixo do limite de detecção da técnica (Smith & Sherman 1994, Andrés et al 2005. Ainda, é possível que tenha ocorrido o clearance (limpeza) pró-viral tenha ocorrido, no qual o ADCC (Antibody dependent cellular cytotoxicity) e/ou anticorpos neutralizantes tenham papel fundamental (Herrmann-Hoesing et al 2007, Barquero et al 2013b. Gregory et al (2011), utilizando as técnicas de PCR e Nested-PCR para detecção do cDNA em amostras de leite, observaram 19,4% (14/72) amostras positivas na primeira reação e 22,2% (16/72) na segunda.…”