Phylogenetic analysis of small ruminant lentiviruses from Northern Brazil

Genetic and antigenic characterization of Brazilian SRLV strains: Natural small ruminant interspecies transmission from mixed herds

Cross-species transmission events and mixed infection of small ruminant lentiviruses (SRLVs) were studied in seven goats and two sheep from three small ruminant mixed flocks from Northeast and Southeast Brazil. Genetic and antigenic analyses with gag/env genes and ELISA multiepitope SU1/SU5 recombinant antigens were carried out, respectively. The genetic analysis of gag and env sequences showed high viral diversity in both species, MVV-like (subtype A1) and CAEV-like B1 in goats, and CAEV-like (subtype B1) in sheep, revealing SRLV interspecies transmission from sheep to goats and vice versa in Brazilian farms. Two Brazilian caprine lentiviruses were segregated in two new genetic clades based on gag analyses, which suggests a new classification into heterogenic genotype A. Furthermore, goat isolates were grouped into subtype A1 and B1 clusters. Cross-reactive antibodies were detected in goats using ELISA with a recombinant antigen carrying SU1 and SU5 immunodominant epitopes; the results showed anti-CAEV and MVV antibodies in goats and anti-CAEV antibodies in sheep. This result can be associated with the high divergence in the V4 region due to SRLV variability. All results confirm cross-species infection of SRLV in Brazilian mixed herds.

Duplex nested-PCR for detection of small ruminant lentiviruses

Small ruminant lentiviruses (SRLV) have high genetic variability which results in different viral strains around the world. This create a challenge to design sensible primers for molecular diagnosis in different regions. This work proposes a protocol of duplex nested-PCR for the precise diagnosis of SRLV. The technique was designed and tested with the control strains CAEV Co and MVV 1514. Then, field strains were submitted to the same protocol of duplex nested-PCR. Blood samples of sheep and goats were tested with AGID and nested PCR with specific primers for pol, gag and LTR. The AGID results showed low detection capacity of positive animals, while the nested PCR demonstrated a greater capacity of virus detection. Results demonstrated that LTR-PCR was more efficient in detecting positive sheep samples, whereas gag-PCR allowed a good detection of samples of positive goats and positive sheep. In addition, pol-PCR was more efficient with goat samples than for sheep. Duplex nested PCR performed with standard virus samples and field strains demonstrated that the technique is more efficient for the detection of multiple pro-viral DNA sequences. This study demonstrated a successful duplex nested PCR assay allowing a more accurate diagnosis of SRLV.

Caprine lentivirus in sheep milk and semen

ABSTRACT With the objective of detecting the presence of caprine lentivirus (CLV) in ewe milk and in ram semen, ten matrixes and four reproducers experimentally infected with CLV were used. Samples of ewe milk were collected during the four months of lactation, five collections per animal, totaling 50 samples. Regarding the rams, eight semen collections were made per animal, during one year of experimentation, totaling 32 samples. The milk and semen samples were submitted to DNA extraction and the nested polymerase chain reaction test (nPCR) to detect CLV proviral DNA. Eight (16%) of the milk samples were positive in nPCR originating from two ewes. Only one (3.12%) semen sample was positive. The amplification products were sequenced, and were confirmed to be a CLV genomic sequence. Thus, the presence of CLV proviral DNA in sheep milk and semen was demonstrated, confirming the feasibility of infection between species, and alerting to the risk of spreading infections.

Small ruminant lentiviruses: genetic variability, tropism and diagnosis

Small ruminant lentiviruses (SRLV) cause a multisystemic chronic disease affecting animal production and welfare. SRLV infections are spread across the world with the exception of Iceland. Success in controlling SRLV spread depends largely on the use of appropriate diagnostic tools, but the existence of a high genetic/antigenic variability among these viruses, the fluctuant levels of antibody against them and the low viral loads found in infected individuals hamper the diagnostic efficacy. SRLV have a marked in vivo tropism towards the monocyte/macrophage lineage and attempts have been made to identify the genome regions involved in tropism, with two main candidates, the LTR and env gene, since LTR contains primer binding sites for viral replication and the env-encoded protein (SU ENV), which mediates the binding of the virus to the host’s cell and has hypervariable regions to escape the humoral immune response. Once inside the host cell, innate immunity may interfere with SRLV replication, but the virus develops counteraction mechanisms to escape, multiply and survive, creating a quasi-species and undergoing compartmentalization events. So far, the mechanisms of organ tropism involved in the development of different disease forms (neurological, arthritic, pulmonary and mammary) are unknown, but different alternatives are proposed. This is an overview of the current state of knowledge on SRLV genetic variability and its implications in tropism as well as in the development of alternative diagnostic assays.

PRIMEIRO ISOLAMENTO DE LENTIVÍRUS DE PEQUENOS RUMINANTES EM CAPRINO NATURALMENTE INFECTADO EM REBANHO DO RIO GRANDE DO NORTE, BRASIL

RESUMO O Vírus da Artrite Encefalite Caprina (CAEV) e Vírus Maedi-visna (MVV) pertencem ao gênero Lentivírus da família Retroviridae. São considerados geneticamente distintos, mas antigenicamente relacionados. O objetivo desde trabalho foi isolar o vírus da CAE de um animal oriundo de um rebanho do Rio Grande do Norte e positivo pelo teste de Imunodifusão em Gel de Agarose (IDGA) através do co-cultivo de leucócitos infectados do sangue periférico em Membrana Sinovial Caprina (MSC). Dezesseis caprinos da raça Saanen, com suspeitas clínicas para CAE foi testado por IDGA e Western Blotting. Para o isolamento viral, os leucócitos do sangue periférico foram isolados por co-cultivo em MSC. Monócitos/Macrófagos coletados foram inoculados em monocamadas pré-formadas em garrafas A25. O resultado do IDGA foi positivo para um animal, confirmado por Western Blotting. Após 50 dias de co-cultivo, foi realizada a coloração da monocamada com cristal de violeta a 0,1% para visualização do ECP e realizada nested-PCR do sobrenadante do co-cultivo, com confirmação do efeito citopático viral. A cepa isolada, denominada BrRN-CNPC.G1 foi considerada o primeiro isolamento do CAEV no Estado do Rio Grande do Norte. Esse estudo permitirá em breve, realizar a caracterização molecular do genoma do vírus isolado, através da análise de seus diferentes genes estruturais e comparar com outras sequencias virais isoladas para identificar a provável origem da infecção desse animal e estabelecer as possíveis divergências entre cepas padrões de Lentivírus e cepas regionais circulantes.