Conserved sequence motifs involving the tat reading frame of Brazilian caprine lentiviruses indicate affiliations to both caprine arthritis-encephalitis virus and visna-maedi virus

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.

Soroprevalência da infecção por lentivírus de pequenos ruminantes em abatedouros do estado de Pernambuco, Brasil

RESUMO: A soroprevalência da infecção por lentivírus de pequenos ruminantes (LVPR) foi determinada em amostras de soros sanguíneos de caprinos e ovinos de aptidão cárnea provenientes de abatedouros de dez municípios do estado de Pernambuco, Brasil. O diagnóstico sorológico ocorreu por meio da imunodifusão em gel de agarose (micro-IDGA) com antígenos dos vírus artrite encefalite caprina (CAE)/Maedi-Visna. Entre as 369 amostras de caprinos, 7(1,89%) (0,8-3,9%) eram soropositivas, e, entre as 383 de ovinos, 1 (0,26%) (0,0-1,4%) estava infectada. Os 7 caprinos soropositivos procederam dos abatedouros públicos dos municípios de Gravatá (n=2), Sertânia (n=4) e Timbaúba (n=1), e o ovino soropositivo veio do abatedouro público de Serra Talhada. A soroprevalência da infecção por LVPR em pequenos ruminantes oriundos de abatedouros do estado de Pernambuco, de 1,06% (8/752), é considerada baixa.

Molecular characterization of the gag gene of caprine arthritis encephalitis virus from goats in the Philippines

Caprine arthritis encephalitis virus (CAEV) causes caprine arthritis encephalitis syndrome, which is an emerging disease of goats in the Philippines. DNA sequence analysis showed homology of 86-93 % between Philippine CAEV and available CAEV sequences in GenBank. CAEV was detected using nested polymerase chain reaction (PCR), and new sets of primers were designed in order to amplify the gag gene, which is a highly conserved region of the viral genome. In addition, the Philippine CAEV isolate clustered in group B with the prototype caprine lentivirus. Based on amino acid sequence alignments, it is possible that the Philippine CAEV isolate is a new strain of CAEV, but it is also possible that it was already present in the country even before the start of goat importation. Molecular characterization of the CAEV gag gene is important for the development of a detection kit specific for the local strain of CAEV and the establishment of small ruminant lentivirus eradication programs in the Philippines. This study is the first report to describe the molecular characteristics of CAEV circulating in the Philippines.

Padronização do Elisa indireto e Western Blot para diagnóstico da artrite-encefalite caprina

A artrite-encefalite caprina (CAE) é diagnosticada rotineiramente pela técnica de imunodifusão em gel de agarose (IDGA), que é considerada pouco sensível. Objetivou-se com este estudo padronizar testes de Elisa-i e Western Blot (WB) para diagnóstico precoce de anticorpos em caprinos contra CAEV e comparar os resultados obtidos nesses testes com a prova de IDGA. Para a padronização dos testes Elisa-i e WB, utilizaram-se diferentes concentrações e diluições de antígeno, soros e conjugado. No Elisa-i, adotaram-se microplacas rígidas com 96 poços, sendo a combinação de concentração de 0,5µg/poço de antígeno e diluições de 1:100 de soro e 1:1500 de conjugado a que apresentou melhor resultado. No WB foram utilizadas membranas de nitrocelulose, definindo-se as diluições de 1:50 de soro e 1:15000 de conjugado. Para avaliar o desempenho das técnicas, 222 amostras de soro caprino foram testadas e os dados obtidos foram comparados com o IDGA. A sensibilidade e a especificidade do Elisa-i/IDGA, WB/IDGA e WB/Elisa-i foram de 70% e 91%, 100% e 72,6%, 84,6% e 76,5%, concomitantemente. O índice Kappa desses testes foi de 0,35, 0,2 e 0,36, respectivamente. As técnicas de Elisa-i e WB apresentaram-se mais sensíveis que a IDGA, podendo ser utilizadas como ferramentas para o diagnóstico precoce da CAE.

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.

Influence of chronic caprine arthritis-encephalitis virus infection on the population of peripheral blood leukocytes

The influence of caprine arthritis-encephalitis (CAE) virus infection on the population of peripheral blood leukocytes in goats was evaluated. For this purpose two groups of adult dairy female goats were formed. The experimental group consisted of 17 goats, which had been naturally infected for many years. The control group comprised 29 non-infected goats, which originated from CAE-free herd. All goats were clinically healthy. Whole blood was collected and tested in hematological analyzer and light microscope to assess the total number of leukocytes and the percentage of four leukocyte populations--neutrophils, eosinophils, monocytes and lymphocytes. Then, flow cytometry with monoclonal antibodies against several surface antigens (namely CD14, CD2, B-B2, CD4, CD8h, TCR-N6, WC1-N2 and WC1-N3) was performed to assess the proportion of lymphocyte subpopulations. Statistically significant differences (alpha < or = 0.01) were observed only in the subpopulations of T lymphocytes--percentage of all subpopulations were significantly higher in the group of seropositive goats. No statistically significant differences were revealed with respect to the total number of blood leukocytes, the average percentage of blood leukocyte populations and proportions of both T and B lymphocytes.

DETECÇÃO DO VÍRUS DA ARTRITE ENCEFALITE CAPRINA NO SÊMEN ATRAVÉS DAS TÉCNICAS DE PCR E NESTED-PCR

RESUMO A Artrite Encefalite Caprina é uma enfermidade de caráter multissistêmico afetando animais de qualquer idade e sexo; causado por um Lentivirus caprino pertencente ao grupo de Lentivirus de Pequenos Ruminantes. Os sintomas conhecidos são leucoencefalomielite, pneumonia intersticial crônica, artrite e mastite intersticial endurativa. Foi descrito que machos soropositivos apresentavam sêmen infectado pelo Lentivirus e processo inflamatório gradual do testículo. A detecção em amostras de sêmen pelas técnicas de PCR e nested-PCR são caracterizadas como métodos de altas especificidade e sensibilidade provendo resultados rápidos. O objetivo do estudo foi detectar, por meio da técnica molecular de PCR e nested-PCR, a presença de DNA pró-viral do Lentivirus caprino em amostras de sêmen de reprodutores criados no Estado de São Paulo. Das 17 amostras, cinco (29,4%) apresentaram a detecção do vírus provando que há a presença de partículas virais no sêmen dos caprinos reprodutores soropositivos a Atrite Encefalite Caprina estudados.

Impact of natural sheep-goat transmission on detection and control of small ruminant lentivirus group C infections

Dissemination of small ruminant lentivirus (SRLV) infections in Norway is affected by the different control strategies used for maedi-visna virus (MVV) infections in sheep and caprine arthritis-encephalitis virus (CAEV) infections in goats. Here we investigated SRLV phylogenetic group variants in sheep. CAEV-like isolates, belonging to phylogenetic group C, were found among both seropositive sheep and goats in mixed flocks, in which sheep and goats are kept together. Intra-herd clustering confirmed that mixed flock animals were infected by the same virus variant, suggesting ongoing interspecies transmission. Few sheep flocks were found to be infected with the MVV-like phylogenetic group A. The apparent absence of SRLV group A type in goats is probably due to the MVV control programme and animal management practices. SRLV group C targets lungs and mammary glands in sheep, and induces typical SRLV pathological lesions. SRLV group C isolated from the sheep mammary glands suggested a productive infection and potential for transmission to offspring. SRLV group C was most prevalent among goats. A lower PCR sensitivity in seropositive sheep suggested a lower load of SRLV group C provirus in sheep than in goats. Higher genetic divergence of group C than in other SRLV groups and extensive heterogeneity among group C isolates in the matrix C-terminal region demonstrate the need for identifying conserved target regions when developing PCR protocols for SRLV detection. As sheep and goats may serve as reservoirs for all SRLV genogroup types, successful control programmes require inclusion of both species.

Molecular characterization of lentiviruses from goats from Poland based on gag gene sequence analysis

Caprine arthritis-encephalitis virus (CAEV) infection in goats is worldwide but with higher prevalence in industrialized countries. While positive serology of CAEV in Polish goats was reported there was no genetic study of this virus. In this study, we described the molecular characterization of lentiviruses isolated from seropositive goats from Poland. We cloned and sequenced a fragment from the gag gene covering part of the coding sequences for the matrix (MA) p17 and for the capsid (CA) p25 proteins. Resulting nucleotide sequences were aligned with those from other ovine/caprine lentivirus isolates. We present data showing that the sequences of most goat lentivirus isolates are closer to the prototypic CAEV-Co isolate, nevertheless from one goat we isolated a virus that is closer to the sheep Maedi Visna virus (MVV) isolate. This might indicate a recent cross-species infection from sheep to goat.

Natural transmission and comparative analysis of small ruminant lentiviruses in the Norwegian sheep and goat populations

Serological surveys for small ruminant lentivirus (SRLV) infections have revealed seropositive sheep in several mixed herds, where sheep are kept together with seropositive goats. Here we have examined the genetic relationships in LTR, pol and env surface unit (SU) and the growth patterns in goat (GSM) and sheep (FOS) synovial membrane cell cultures of SRLV isolates obtained from both mixed and single species herds. Phylogenetic analyses of pol and env SU revealed that Norwegian SRLVs derived from both goat and sheep in mixed herds are distributed into group C, while isolates obtained from unmixed sheep flocks cluster in group A, together with maedi-visna-like representatives of the A1 subtype. In this study, the direction of group C virus transmission is proposed to be from goat to sheep. The replication efficiency in GSM and FOS cultures and the cytopathic phenotype induced by the SRLV isolates gave no indication of any species-specific characteristics. No particular nucleotide sequences of the LTR-U3 region or env SU were identified that could be related to cytopathic phenotype. This study shows that sheep in Norway harbour SRLVs belonging to phylogenetic groups A and C, and this provides further evidence for cross-species infection being a regular characteristic of SRLVs, which may represent an important source for viral persistence.

LENTIVÍRUS DE PEQUENOS RUMINANTES EM OVINOS SANTA INÊS: ISOLAMENTO, IDENTIFICAÇÃO PELA PCR E INQUÉRITO SOROLÓGICO NO ESTADO DE PERNAMBUCO

RESUMO Os pequenos ruminantes podem ser infectados por um grupo de vírus genericamente denominado de Lentivírus de Pequenos Ruminantes (LVPR), que compreende vários isolados, distribuídos em quatro grupos filogenéticos. Os vírus Maedi-Visna (MVV) e da Artrite Encefalite Caprina (CAEV), originalmente, isolados de ovinos e caprinos, respectivamente, são os protótipos dos dois grupos. O objetivo desse trabalho foi isolar, identificar amostra de LVPR e realizar levantamento sorológico, em ovinos da raça Santa Inês. Através do co-cultivo de células de membrana sinovial ovina e sangue periférico de um ovino soropositivo ao teste de IDGA foi isolado LVPR, amostra BrPe2-01, identificada pelo aparecimento de sincícios nas monocamadas e pela reação em cadeia da polimerase (PCR). A sorologia foi feita através do teste de Imunodifusão em Gel de Agar (IDGA) em animais de 25 propriedades procedentes das regiões Agreste, Sertão, Mata Meridional e Metropolitana do Estado de Pernambuco, totalizando 558 amostras. Os resultados demonstraram sorologia positiva em 6 (1,07%) ovinos de 3 (12%) rebanhos estudados. Concluiu-se que os ovinos da raça Santa Inês estão sendo infectados pelos LVPR, porém com baixa prevalência.

Molecular characterization and phylogenetic study of Maedi Visna and Caprine Arthritis Encephalitis viral sequences in sheep and goats from Spain

Small ruminant lentiviruses (SRLV) are widely spread in many countries, including Spain. However, little is known about the genetic characteristics of Spanish goat and sheep SRLV. In this study, segments from three genomic regions (pol, gag-p25 and LTR) were amplified using DNA isolated from three Spanish autochthonous sheep (one) and goats (two). Animals (one per flock) belonged to distantly located, single-species flocks (goat or sheep). Sequence analysis showed conservation of regions that are putatively relevant to viral survival. Sequences of Spanish goat and sheep SRLV were allocated into phylogenetic trees (phylograms) with known SRLV groups. The phylograms corresponding to the pol, gag-p25 and LTR regions analyzed presented a compatible topology. This showed that Spanish caprine and ovine SRLV sequences belonged to the A or D phylogenetic groups and were closer to sheep SRLV prototypes (A1 group) than to goat SRLV prototypes (B or C groups), according to the current classification [Shah, C., Boni, J., Huder, J.B., Vogt, H.R., Muhlherr, J., Zanoni, R., Miserez, R., Lutz, H., Schupbach, J., 2004a. Phylogenetic analysis and reclassification of caprine and ovine lentiviruses based on 104 new isolates: evidence for regular sheep-to-goat transmission and worldwide propagation through livestock trade. Virology 319 (1), 12-26]. It was not possible to amplify in the three genetic regions the expected fragment in additional Spanish caprine and ovine SRLV proviral DNA sequences with the PCR primers used. This suggests that there is heterogeneity at the primer binding site among Spanish SRLV sequences. It also illustrates the need to develop diagnostic tests that are sensitive in local breeds.

Distribution and heterogeneity of small ruminant lentivirus envelope subtypes in naturally infected French sheep

Small ruminants lentiviruses (SRLV) nucleotide sequences spanning the V1V2 variable regions of the env gene were amplified by nested-PCR from 38 blood samples collected from 16 naturally infected sheep flocks in France. For the rapid SRLV group determination of field isolates, the PCR-amplified fragments were subjected to a SRLV-adapted heteroduplex mobility assay (HMA). All viral sequences were clearly assignable to the SRLV group B by HMA analysis. Twenty-seven SRLV isolates were selected for DNA sequence analysis. In each case, nucleotide comparison and phylogenetic analyses confirmed the genetic relationships inferred by HMA. Six SRLV isolates belonged to subtype B1, and 21 pertained to subtype B2, one flock being infected with both subtypes. Subtypes B1 and B2 were found with different frequencies and geographic spread, but exhibited similar genetic diversities. These results give a more complete picture of the distribution and heterogeneity of SRLV env subtypes in sheep and confirmed that multiple interspecies transmission occurred in the past. Furthermore, HMA appeared to be a rapid and reliable method to differentiate caprine arthritis encephalitis virus from maedi-visna virus.

Genetic diversity of small-ruminant lentiviruses: characterization of Norwegian isolates of Caprine arthritis encephalitis virus

Small-ruminant lentiviruses (SRLVs), including Caprine arthritis encephalitis virus (CAEV) in goats and maedi-visna virus (MVV) in sheep, are lentiviruses that, despite overall similarities, show considerable genetic variation in regions of the SRLV genome. To gain further knowledge about the genetic diversity and phylogenetic relationships among field isolates of SRLVs occurring in geographically distinct areas, the full-length genomic sequence of a CAEV isolate (CAEV-1GA) and partial env sequences obtained from Norwegian CAEV-infected goats were determined. The genome of CAEV-1GA consisted of 8919 bp. Alignment studies indicated significant diversity from published SRLV sequences. Deletions and hypervariability in the 5′ part of the env gene have implications for the size of the proposed CAEV-1GA Rev protein and the encoded surface glycoprotein (SU). The variable regions in the C-terminal part of SU obtained from Norwegian CAEV isolates demonstrate higher sequence divergence than has been described previously for SRLVs. Phylogenetic analysis based on SU sequences gives further support for a unique group designation. The results described here reveal a distant genetic relationship between Norwegian CAEV and other SRLVs and demonstrate that there is more geographical heterogeneity among SRLVs than reported previously.

First partial characterisation of small ruminant lentiviruses from Greece

Small ruminant lentivirus (SRLV) infections are widespread in Greece, but SRLVs have never been isolated and characterized. In this study, we present the sequence of a 574-nucleotide (191-amino acid) region of the gag gene of SRLV strains from four sheep and one goat from a single geographic area of Greece. All five sequences appeared to be closely related at both nucleotide (2.1-14.2% variation) and deduced amino acid (1.6-4.2% variation) level. Greek SRLV strains were closer to ovine prototypic strains (average divergence 16.8%) than to the caprine strain CAEV-Co (21% divergence). By amino acid composition, the Greek SRLVs were on the average more than twice as distant from CAEV-Co as from other ovine strains. Phylogenetic analysis suggested that Greek strains segregate into a unique group, separate from, but related to, other ovine prototype sequences.

Vírus da artrite encefalite caprina: isolamento e caracterização de parte do gene gag

Amostras de sangue de 12 animais soropositivos pelo teste de imunodifusão em gel de agarose e que não apresentavam sinais clínicos sugestivos de infecção pelo vírus da artrite-encefalite caprina (CAEV) foram coletadas para isolamento viral. Mácrofagos derivados de monócitos foram co-cultivados com células de membrana sinovial caprina (MSC), resultando em cinco amostras que apresentaram efeito citopático característico do tipo persistente, semelhante ao observado para o CAEV. Uma técnica de reação em cadeia de polimerase (PCR) foi padronizada para amplificar parte do gene gag do genoma pró-viral, codificante para a proteína do capsídeo viral (p25). As cinco amostras foram amplificadas pela PCR e três delas, BR-UFMG/PL1, BR-UFMG/PL2 e BR-UFMG/PL3, foram seqüenciadas diretamente dos seus produtos de PCR. O alinhamento múltiplo das seqüências obtidas com outras de lentivírus de pequenos ruminantes (LVPR), obtidas no GenBank, e o dendrograma revelaram que as novas amostras de CAEV são únicas e distintas das demais amostras de LVPR, possuindo maior identidade de nucleotídeos e aminoácidos entre si e com as amostras de CAEV do que com a do vírus maedi-visna.

Clearance of a productive lentivirus infection in calves experimentally inoculated with caprine arthritis-encephalitis virus

Lentiviruses have long been considered host-specific pathogens, but several recent observations demonstrated their capacity to conquer new hosts from different species, genera, and families. From these cross-species infections emerged new animal and human infectious diseases. The successful colonization and adaptation of a lentivirus to a nonnatural host depends on unspecific and specific host barriers. Some of those barriers exert a relative control of viral replication (i.e., cytotoxic T-lymphocyte response, viral inhibitory factors), but none of them was found able to totally clear the infection once the retrovirus is fully adapted in its host. In this study we examined the evolution of the host-lentivirus interactions occurring in an experimental animal model of cross-species infection in order to analyze the efficiency of those barriers in preventing the establishment of a persistent infection. Five newborn calves were inoculated with caprine arthritis-encephalitis virus (CAEV), and the evolution of infection was studied for more than 12 months. All the animals seroconverted in the first 0.75 to 1 month following the inoculation and remained seropositive for the remaining time of the experiment. Viral infection was productive during 4 months with isolation of replication competent virus from the blood cells and organs of the early euthanized animals. After 4 months of infection, neither replication-competent virus nor virus genome could be detected in blood cells or in the classical target organs, even after an experimental immunosuppression. No evidence of in vitro restriction of CAEV replication was observed in cells from tissues explanted from organs of these calves. These data provide the demonstration of a natural clearance of lentivirus infection following experimental inoculation of a nonnatural host, enabling perspectives of development of new potential vaccine strategies to fight against lentivirus infections.

Lack of trans-activation function for Maedi Visna virus and Caprine arthritis encephalitis virus Tat proteins

All lentiviruses contain an open reading frame located shortly upstream or inside of the env gene and encoding a small protein which has been designated Tat. This designation was mainly with respect to the positional analogy with the first exon of the trans-activator protein of the well studied human immunodeficiency virus type 1 (HIV-1). In this work we comparatively studied the trans- activation activity induced by Tat proteins of the small ruminant Maedi Visna virus (MVV) of sheep and Caprine arthritis encephalitis virus (CAEV) of goats on MVV and CAEV LTRs with that induced by the human lentivirus HIV-1 on its own LTR. The HIV-1 LTR alone weakly expresses the reporter GFP gene except when the HIV-1 Tat protein is coexpressed, the GFP expression is increased 60-fold. In similar conditions only minimal trans-activation increasing two- to three-fold the MVV and CAEV LTR activity was found with MVV Tat protein, and no trans-activation activity was detected in any used cell type or with any virus strain when CAEV Tat was tested. These results indicate that the small ruminant lentiviruses (SRLV) differ from the primate lentiviruses in their control of expression from the viral LTRs and put into question the biological role of the encoded protein named "Tat."

Characterisation of an Irish caprine lentivirus strain--SRLV phylogeny revisited

Small ruminant lentiviruses (SRLV), i.e. caprine arthritis-encephalitis virus (CAEV) (which infects goats) and maedi-visna virus (MVV) (which infects sheep) are two closely related lentiviruses but the relationship between goat and sheep lentiviruses has not been clearly established. To better understand their genetic relationship, we reinvestigated the phylogeny of SRLV using new sequences from an Irish and a Norwegian strain together with sequences available from databases. The phylogenetic analyses were carried out on the gag, pol and env fragments using four methods: neighbor-joining (NJ), Fitch and Margoliash (Fitch), Fitch and Wagner parsimony (Pars) and maximum likelihood (ML). The tree topologies were consistent whether derived from any of the four methods or any of the gene fragments, but the phylogenetic analyses in the pol and env regions were more informative than in the gag region. The Tamura-Nei model with variable rates across sites (described by a gamma distribution) provides a more accurate description of SRLV evolution than simple methods. The newly described Irish lentivirus strain, which was isolated from a goat, was closely related to the lentivirus that infects sheep: MVV. The novel Norwegian CAEV strain belonged to a cluster specific to the CAEV strains from Norway. Together, both data confirm the previously reported subdivision of the different SRLV strains into six clades. The caprine and ovine lentivirus sequences are interspersed in phylogenetic trees, supporting the existence of cross-species transmission. Nevertheless, the transmission of an ovine lentivirus to a goat could trigger the emergence of some goat-adapted phylums. Our new sequences confirm the complex situation in SRLV phylogeny but more sequences are needed to elucidate more precisely the relationship between SRLV.

Phylogenetic analysis of small ruminant lentiviruses from Southern Brazil

The first lentivirus isolated from sheep in Brazil was analysed phylogenetically. Evolutionary trees of the proviral 597 nucleotide gag and 432 nucleotide pol sequences obtained by the maximum likelihood method demonstrated that the sheep isolate clustered with prototype Maedi Visna virus whereas three lentiviruses isolated from goats in the same geographic region were close to caprine arthritis encephalitis prototypes. A subsequent comparison of sequence data of these viruses with those contained in the EMBL sequence database revealed that, in contrast to caprine prototypic viruses, all prototypic Maedi Visna viruses contain a deletion of six nucleotides in the gag gene resulting in the deletion of two residues in the central region of capsid protein. This deletion may be a useful marker in the analysis of small ruminant lentiviruses, especially when considering possible transmission of lentiviruses between sheep and goats.

Lentivírus de pequenos ruminantes (CAEV e Maedi-Visna): revisão e perspectivas

Os lentivírus de pequenos ruminantes (SRLV), cujos protótipos são os vírus da Artrite-Encefalite Caprina (CAEV) e Maedi-Visna, são patógenos amplamente distribuidos, os quais causam doenças degenerativas progressivas lentas em caprinos e ovinos, determinando importantes perdas econômicas. Estes vírus causam infecções persistentes com período de incubação longo e causam inflamatórias e degenerativas. As lesões são induzidas em tecidos específicos do hospedeiro como articulações, pulmões, CNS e glandulas mamárias devido à replicação viral em células da linhagem monocítico-fagocitária que são as principais células-alvo. A infecção ocorre principalmente durante os primeiros meses de vida, através da ingestão de vírus no leite ou colostro de cabras ou ovelhas infectadas. A indução da resposta imunológica é variável e não protege contra a infecção. O diagnóstico é baseado primariamente na detecção de anticorpos para SRLV, geralmente por imunodifusão em gel de agar (AGID) e enzyme linked immunosorbent assay (ELISA). O diagnóstico e separação ou descarte dos animais soropositivos associado ao uso de certas práticas de manejo, especialmente das crias, são os principais meios implementados para prevenir a disseminação de SRLV, uma vez que ainda não existe vacina contra o vírus. As estratégias adotadas pelos SRLV para enfrentar o sistema imune dificultam o diagnóstico da infecção, controle ou prevenção da disseminação de SRLV. Esta revisão apresenta alguns aspectos das lentivíroses de pequenos ruminantes baseadas em estudos filogenéticos de amostras isoladas, aspectos clínicos e imunopatológicos.