Recombinant small ruminant lentivirus subtype B1 in goats and sheep of imported breeds in Mexico

Genetic Characterization of Small Ruminant Lentiviruses Isolated from Dairy Sheep in Greece

The high genetic heterogeneity of small ruminant lentiviruses (SRLV) renders the genetic characterization of the circulating strains crucial for the epidemiological investigation and the designation of effective diagnostic tools. In Greece, research data regarding the genetic diversity of the circulating SRLV strains is scarce, hindering the implementation of efficient surveillance and control programs. The objective of the study was to genetically characterize SRLV strains isolated from intensive dairy sheep farms in Greece and evaluate the variability of the immunodominant regions of the capsid protein. For this reason, a total of 12 SRLV-infected animals from four intensive dairy sheep farms with purebred Chios and Lacaune ewes were used for the amplification and sequencing of an 800 bp gag-pol fragment. The phylogenetic analyses revealed a breed-related circulation of strains; Chios ewes were infected with strains belonging exclusively to a separate group of genotype A, whereas strains belonging to subtype B2 were isolated from Lacaune ewes. Immunodominant epitopes of capsid protein were quite conserved among the strains of the same genotype, except for the Major Homology Region which showed some unique mutations with potential effects on viral evolution. The present study contributes to the extension of the current knowledge regarding the genetic diversity of SRLV strains circulating in sheep in Greece. However, broader genetic characterization studies are warranted for the exploration of possible recombinant events and the more comprehensive classification of the circulating strains.

The genetic variability of small-ruminant lentiviruses and its impact on tropism, the development of diagnostic tests and vaccines and the effectiveness of control programmes

Introduction

Maedi-visna virus and caprine arthritis encephalitis virus are two closely related lentiviruses which cause multisystemic, progressive and persistent infection in goats and sheep. Because these viruses frequently cross the species barrier, they are considered to be one genetic group called small-ruminant lentiviruses (SRLV). They have in vivo tropism mainly for monocytes and macrophages and organ tropism with unknown mechanisms. Typical clinical signs are pneumonia in sheep, arthritis in goats, and mastitis in both species. Infection with SRLV cannot currently be treated or prevented, and control programmes are the only approaches to avoiding its spread. These programmes rely mainly on annual serological testing and elimination of positive animals. However, the high genetic and antigenic variability of SRLV complicate their early and definitive diagnosis. The objective of this review is to summarise the current knowledge of SRLV genetic variation and its implications for tropism, the development of diagnostic tests and vaccines and the effectiveness of control and eradication programmes.

Material and Methods

Subject literature was selected from the PubMed and the Google Scholar databases.

Results

The high genetic diversity of SRLV affects the performance of diagnostic tools and therefore control programmes. For the early and definitive diagnosis of SRLV infection, a combination of serological and molecular tests is suggested. Testing by PCR can also be considered for sub-yearling animals. There are still significant gaps in our knowledge of the epidemiology, immunology and biology of SRLV and their impact on animal production and welfare.

Conclusion

This information may aid selection of the most effective SRLV spread reduction measures.

Small ruminant lentivirus capsid protein (SRLV-p25) antigenic structural prediction and immunogenicity to recombinant SRLV-rp25-coupled to immunostimulatory complexes based on glycyrrhizinic acid

Small ruminant lentiviruses (SRLV) infect sheep and goats resulting in significant economic losses. This study evaluated for the first time the predicted conformational structure of the SRLV-capsid-protein 25 (SRLV-p25) and analyzed the antigenicity of recombinant protein (SRLV-rp25) in mice by coupling to an immunostimulatory complexes based on glycyrrhizinic acid liposomes (GAL) and tested plasma from goats and sheep naturally infected. Analysis in silico and conformational structure of SRLV-p25 (genotype B-FESC-752) showed similar characteristics to other lentiviral capsids. The efficient expression of SRLV-rp25 was confirmed by Western blot. The humoral immune responses in mice showed an increased level of antibodies from day 21 to 35 of the SRLV-rp25-GAL and SRLV-rp25-ISCOM® groups and the cellular immune response showed no significant difference in IL-10 levels (P >.05), however, a significant difference (P <.001) was observed when comparing SRLV-rp25-GAL with SRLV-rp25 groups. Immunoreactivity toward SRLV-rp25 revealed 61% of positive samples from naturally infected goats and sheep.

Small ruminant lentivirus capsid protein (SRLV-p25) antigenic structural prediction and immunogenicity to recombinant SRLV-rp25-coupled to immunostimulatory complexes based on glycyrrhizinic acid

Small ruminant lentiviruses (SRLV) infect sheep and goats resulting in significant economic losses. This study evaluated for the first time the predicted conformational structure of the SRLV-capsid-protein 25 (SRLV-p25) and analyzed the antigenicity of recombinant protein (SRLV-rp25) in mice by coupling to an immunostimulatory complexes based on glycyrrhizinic acid liposomes (GAL) and tested plasma from goats and sheep naturally infected. Analysis in silico and conformational structure of SRLV-p25 (genotype B-FESC-752) showed similar characteristics to other lentiviral capsids. The efficient expression of SRLV-rp25 was confirmed by Western blot. The humoral immune responses in mice showed an increased level of antibodies from day 21 to 35 of the SRLV-rp25-GAL and SRLV-rp25-ISCOM® groups and the cellular immune response showed no significant difference in IL-10 levels (P &gt;.05), however, a significant difference (P &lt;.001) was observed when comparing SRLV-rp25-GAL with SRLV-rp25 groups. Immunoreactivity toward SRLV-rp25 revealed 61% of positive samples from naturally infected goats and sheep.

Pathological, molecular, and serological study of small ruminant lentiviruses in Jordan

Background and Aim:

Maedi-visna is a chronic viral disease of sheep with worldwide distribution causing substantial economic losses to the small ruminant industry. Pneumonia and mastitis are the main manifestations of the disease. This study aimed to investigate the occurrence of maedi-visna virus (MVV) in sheep using histopathology and nested polymerase chain reaction (PCR) techniques and also to estimate the seroprevalence of small ruminant lentiviruses (SRLVs) in sheep and goats using commercially available enzyme-linked immunosorbent assay (ELISA).

Materials and Methods:

Lung tissue samples from 380 sheep were collected and fixed in 10% formalin for histopathology and molecular diagnosis of MVV. Separately, 806 serum samples were randomly collected from 633 sheep and 173 goats to detect the seroprevalence of SRLVs using ELISA.

Results:

The results showed that 4.7% of lung samples (n=190) were positive by both histopathology and nested PCR, 5.8% (n = 380) were positive by histopathology only (have lymphoid follicular hyperplasia), and 7.4% (n = 190) were positive by nested PCR only. Statistical analysis revealed a moderate agreement between the two tests (Kappa=0.451, n = 190). Serology results revealed that sheep and/or goats herd prevalence was 59.8% (n = 87), while individual seroprevalence in sheep (40.1%, n = 633) was significantly higher than that in the other six countries and also significantly higher than that in goats (18.5%, n = 173) (at p < 0.05).

Conclusion:

The moderate statistical agreement between nested PCR and histopathological diagnosis of MVV in formalin-fixed paraffin-embedded sheep lung tissue samples (Kappa=0.451, n = 190) suggests combining both tests for more sensitive MVV detection in sheep lung samples. SRLVs seropositivity in sheep was significantly higher than in goats, thus, it is of high concern and urges the inquiry into the economic impact of the disease and the financial benefit of adopting eradication measures.

Genetic Characterization of Small Ruminant Lentiviruses (SRLVs) Circulating in Naturally Infected Sheep in Central Italy

Small ruminant lentiviruses (SRLVs) represent a very heterogeneous group of ss-RNA viruses that infect sheep and goats worldwide. They cause important, deleterious effects on animal production and limit the animal trade. SRLVs show a high genetic variability due to high mutation rate and frequent recombination events. Indeed, five genotypes (A–E) and several subtypes have been detected. The aim of this work was to genetically characterize SRLVs circulating in central Italy. On this basis, a phylogenetic study on the gag-pol genetic region of 133 sheep, collected from 19 naturally infected flocks, was conducted. In addition, to evaluate the frequency of mutation and the selective pressure on this region, a WebLogo 3 analysis was performed, and the dN/dS ratio was computed. The results showed that 26 samples out of 133 were clustered in genotype A and 106 samples belonged to genotype B, as follows: A9 (n = 8), A11 (n = 10), A24 (n = 7), B1 (n = 2), B2 (n = 59), and B3 (n = 45). No recombination events were found. Mutations were localized mainly in the VR-2 region, and the dN/dS ratio of 0.028 indicated the existence of purifying selection. Since the genetic diversity of SRLVs could make serological identification difficult, it is important to perform molecular characterization to ensure a more reliable diagnosis, to maintain flock health status, and for the application of local and national control programs.

Genomic Epidemiology and Heterogeneity of SRLV in Italy from 1998 to 2019

Small ruminant lentiviruses (SRLV) are viruses that retro-transcribe RNA to DNA and show high rates of genetic variability. SRLV affect animals with strains specific for each host species (sheep or goats), resulting in a series of clinical manifestations depending on the virulence of the strain, the host’s genetic background and farm production system. The aim of this work was to present an up-to-date overview of the genomic epidemiology and genetic diversity of SRLV in Italy over time (1998–2019). In this study, we investigated 219 SRLV samples collected from 17 different Italian regions in 178 geographically distinct herds by CEREL. Our genetic study was based on partial sequencing of the gag-pol gene (800 bp) and phylogenetic analysis. We identified new subtypes with high heterogeneity, new clusters and recombinant forms. The genetic diversity of Italian SRLV strains may have diagnostic and immunological implications that affect the performance of diagnostic tools. Therefore, it is extremely important to increase the control of genomic variants to improve the control measures.

Classification of small ruminant lentivirus subtype A2, subgroups 1 and 2 based on whole genome comparisons and complex recombination patterns

Background: Small ruminant lentiviruses (SRLVs) cause a multisystemic chronic wasting disease in sheep across much of the world. SRLV subtype A2 is prevalent in North America and further classified into multiple subgroups based on variation in the group antigens gene (gag) and envelope (env) genes. In sheep, the ovine transmembrane protein 154 (TMEM154) gene is associated with SRLV susceptibility. Ewes with at least one copy of TMEM154 encoding a full-length protein with glutamate at position 35 (E35; haplotypes 2 and 3), are highly susceptible to SRLV infection while ewes with any combination of TMEM154 haplotypes which encodes lysine (K35; haplotype 1), or truncated proteins (haplotypes 4 and 6) are several times less so. A2 subgroups 1 and 2 are associated with host TMEM154 genotypes; subgroup 1 with the K35/K35 genotype and subgroup 2 with the E35/E35 genotype.

Methods:  Sequence variation within and among full-length assemblies of SRLV subtype A2 subgroups 1 and 2 was analyzed to identify genome-scale recombination patterns and subgroup-specific variants.

Results:  Consensus viral genomes were assembled from 23 infected sheep, including animals of assorted TMEM154 genotypes comprised of haplotypes 1, 2, or 3. Viral genome analysis identified viral subgroups 1 and 2 among the samples, and revealed additional sub-structure within subgroup 2 based on models predicting complex patterns of recombination between the two subgroups in several genomes. Animals with evidence of dual subgroup infection also possessed the most diverse quasi-species and the most highly recombined consensus genomes. After accounting for recombination, 413 subgroup diagnostic single nucleotide polymorphisms (SNPs) were identified.

Conclusions:  The viral subgroup framework developed to classify SRLV consensus genomes along a continuum of recombination suggests that animals with the TMEM154 E35/K35 genotype may represent a reservoir for producing viral genomes representing recombination between A2 subgroups 1 and 2.

Replication of Small Ruminant Lentiviruses in Aluminum Hydroxide-Induced Granulomas in Sheep: a Potential New Factor for Viral Dissemination

Aluminum (Al)-based salts are widely used adjuvants in ruminants and other species to strengthen the immune response elicited against vaccine antigen(s). However, they can lead to the formation of long-lasting granulomas composed of abundant activated macrophages. Small ruminant lentiviruses (SRLV) are widely distributed macrophage-tropic retroviruses that cause persistent infections in sheep and goats. Infected monocytes/macrophages and dendritic cells establish an inflammatory microenvironment that eventually leads to clinical manifestations. The aim of this work was to study the effect of Al-induced granulomas in the replication and pathogenesis of SRLV. Eleven adult, naturally SRLV-infected sheep showing clinical arthritis were distributed in vaccine (n = 6), adjuvant-only (n = 3), and control (n = 2) groups and inoculated with commercial Al-based vaccines, Al hydroxide adjuvant alone, or phosphate-buffered saline, respectively. In vitro studies demonstrated viral replication in Al-induced granulomas in 5 out of 10 sheep. Immunohistochemistry (IHC) evinced granular, intracytoplasmic SRLV presence in macrophages within granulomas. Viral sequences obtained from granulomas, blood monocytes, and other tissues were highly similar in most animals, suggesting virus circulation among body compartments. However, notable differences between isolated strains in granulomas and other tissues in specific animals were also noted. Interestingly, the B2 subtype was the most commonly found SRLV genotype, reaching a wider body distribution than previously described. Recombination events between genotypes B2 and A3 along the gag region were identified in two sheep. Our results indicate that Al-hydroxide-derived granulomas may represent an ideal compartment for SRLV replication, perhaps altering natural SRLV infection by providing a new, suitable target tissue.IMPORTANCE Granulomas are inflammation-derived structures elicited by foreign bodies or certain infections. Aluminum adjuvants included in vaccines induce granulomas in many species. In sheep, these are persistent and consist of activated macrophages. Small ruminant lentiviruses (SRLV), which are macrophage-tropic lentiviruses, cause a chronic wasting disease affecting animal welfare and production. Here, we studied the occurrence of SRLV in postvaccination granulomas retrieved from naturally infected ewes after vaccination or inoculation with aluminum only. SRLV infection was confirmed in granulomas by identification of viral proteins, genomic fragments, and enzymatic activity. The infecting SRLV strain, previously found exclusively in carpal joints, reached the central nervous system, suggesting that occurrence of SRLV in postvaccination granulomas may broaden tissue tropism. SRLV recombination was detected in inoculated animals, a rare event in sheep lentiviruses. Potentially, virus-host interactions within granulomas may modify viral pathogenesis and lead to more widespread infection.

Classification of small ruminant lentivirus subtype A2, subgroups 1 and 2 based on whole genome comparisons and complex recombination patterns

Background: Small ruminant lentiviruses (SRLVs) cause a multisystemic chronic wasting disease in sheep across much of the world. SRLV subtype A2 is prevalent in North America and further classified into multiple subgroups based on variation in the group antigens gene (gag) and envelope (env) genes. In sheep, the ovine transmembrane protein 154 (TMEM154) gene is associated with SRLV susceptibility. Ewes with at least one copy of TMEM154 encoding a full-length protein with glutamate at position 35 (E35; haplotypes 2 and 3), are highly susceptible to SRLV infection while ewes with any combination of TMEM154 haplotypes which encodes lysine (K35; haplotype 1), or truncated proteins (haplotypes 4 and 6) are several times less so. A2 subgroups 1 and 2 are associated with host TMEM154 genotypes; subgroup 1 with the K35/K35 genotype and subgroup 2 with the E35/E35 genotype. Methods:  Sequence variation within and among full-length assemblies of SRLV subtype A2 subgroups 1 and 2 was analyzed to identify genome-scale recombination patterns and subgroup-specific variants. Results:  Consensus viral genomes were assembled from 23 infected sheep, including animals of assorted TMEM154 genotypes comprised of haplotypes 1, 2, or 3. Viral genome analysis identified viral subgroups 1 and 2 among the samples, and revealed additional sub-structure within subgroup 2 based on models predicting complex patterns of recombination between the two subgroups in several genomes. Animals with evidence of dual subgroup infection also possessed the most diverse quasi-species and the most highly recombined consensus genomes. After accounting for recombination, 413 subgroup diagnostic single nucleotide polymorphisms (SNPs) were identified. Conclusions:  The viral subgroup framework developed to classify SRLV consensus genomes along a continuum of recombination suggests that animals with the TMEM154 E35/K35 genotype may represent a reservoir for producing viral genomes representing recombination between A2 subgroups 1 and 2.

Serotyping versus genotyping in infected sheep and goats with small ruminant lentiviruses

Despite SRLV infection being endemic in Mexico, there is little information regarding which genotypes are present. We compared serotyping and PCR-sequencing results from sheep and goats infected with SRLV. We separated plasma and peripheral blood leukocytes (PBL) from 1940 blood samples from sheep and goats from 12 states across Mexico. To detect SRLV infection, we tested plasma samples using two commercial ELISA kits (VMRD and Eradikit SRLV Screening). Then, we serotyped the infecting virus (A/ B) using Eradikit SRLV Genotyping. PBL DNA was used to detect the proviral genome via PCR. Positive amplicons were sequenced to identify viral genotypes using a phylogenetic analysis. Also, we analysed for residues differences in the sequences of a capsid epitope between genotypes. The serological results indicated a higher detection of seropositive animals using the VMRD ELISA compared to Eradikit, with 21 % and 15.3 % more in sheep and goats respectively. Only 25.7 % of the ELISA serotyping results matched those from PCR-sequencing. PCR-sequencing was able to identify genotype A, B and coinfections in animals classified as indeterminate by the ELISA test. This lack of sensitivity may be related to the lack of epitopes from the matrix and transmembrane peptides used by ELISA screening. Sequences analysis revealed that SRLVs found in sheep cluster with genetic subtypes A2 and B1, while those in goats cluster with subtypes A1 and B1. Serotyping did not prove to be an adequate method for predicting the viral genotype (A and / or B) in infections caused by SRLV.

Signature patterns in region V4 of small ruminant lentivirus surface protein in sheep and goats

The env gene in Small Ruminant Lentiviruses (SRLV) encodes the surface glycoprotein (SU) that divides into conserved (C1-C4) and variable regions (V1-V5). SRLV region V4 has been found to be homologous to the V3 region of human lentivirus (HIV). HIV V3 is responsible for tropism and the development of nervous clinical patterns when there is a tendency to conserve amino acids in specific "signature pattern" positions. The goal of this study was to identify signature patterns in the V4 region of the SU, which is encoded by the SRLV env gene. Secondarily, to understand how these signature patterns are associated with different clinical status in naturally infected sheep and goats. Starting with 244 samples from seropositive animals from nine Mexican states, we amplified the V4 region using nested PCR and obtained 49 SRLV sequences from peripheral blood leukocytes. Based on phylogenetic analysis results, we identified three groups: asymptomatic genotypes A (Ssx GA) and B (Ssx GB), as well as animals with arthritic presentation, genotype B (A GB). Similarity levels between group sequences ranged from 67.9%-86.7%, with a genetic diversity ranging from 12.7%-29.5% and a dN / dS ratio that indicated negative selection. Analyses using Vespa and Entropy programs identified four residues at positions 54, 78, 79 and 82 in SU region V4 as possible signature patterns, although with variable statistical significance. However, position 54 residues "N" (p = 0.017), "T" (p = 0.001) and "G" (p = 0.024) in groups A GB, Ssx GA and Ssx GB respectively, best characterized the signature patterns. The results obtained identified a signature pattern related to different genotypes and clinical status by SRLV in sheep and goats.

Etiology, Epizootiology and Control of Maedi-Visna in Dairy Sheep: A Review

Maedi-visna (MV) in sheep is caused by maedi-visna virus (MVV), a small ruminant lentivirus (SRLV) that causes chronic infection and inflammatory lesions in infected animals. Pneumonia and mastitis are its predominant clinical manifestations, and the tissues infected by MVV are mainly the lungs, the mammary gland, the nervous system and the joints. MV has a worldwide distribution with distinct MVV transmission patterns depending on circulating strains and regionally applied control/eradication schemes. Nevertheless, the prevalence rate of MV universally increases. Currently, gaps in understanding the epizootiology of MV, the continuous mutation of existing and the emergence of new small ruminant lentiviruses (SRLVs) strains, lack of an effective detection protocol and the inefficiency of currently applied preventive measures render elimination of MV an unrealistic target. Therefore, modifications on the existing MV surveillance and control schemes on an evidentiary basis are necessary. Updated control schemes require the development of diagnostic protocols for the early and definitive diagnosis of MVV infections. The objectives of this review are to summarize the current knowledge in the epizootiology and control of MV in dairy sheep, to describe the research framework and to cover existing gaps in understanding future challenges regarding MV.

Seroprevalence of small ruminant lentivirus (SRLV) infection in wild cervids in Poland

Small ruminant lentiviruses (SRLV) are widespread amongst domesticated sheep and goats worldwide. Infection of wild ruminants in close contact with affected domesticated small ruminants has been proposed as an actor in SRLV epidemiology, but studies are limited. The aim of this study was to estimate the apparent (AP) and estimated prevalence (EP) of exposure to SRLV infection in wild ruminants from Poland. Samples originating from 198 free-living cervids comprising 142 European red deer and 56 roe deer were serologically tested using a multi-epitope recombinant antigen ELISA representing subtypes A1, A13, B1, and B2 of SRLV and a commercial ELISA test. The estimated prevalence of SRLV infection was estimated using the Bayesian approach with models that adjusted for the misclassification of animals because of a small population and lack of sampling method, the imperfect performance of the ELISAs and because sera of different species were tested. The calculated estimated prevalence ranged from 5.3 % (95 % CI 0.3, 12.5) to 24.6 % (95 % CI 3.3, 38.5) for the ELISA with multi-epitope antigens while estimated prevalence using the commercial ELISA was 2.5 % (95 % CI 0.2, 6.6). These results may suggest the existence of a new SRLV reservoir in Poland and highlight the importance of surveilling and controlling SRLV infection in domestic and wild ruminants sharing pasture areas.

Genotyping Based on the LTR Region of Small Ruminant Lentiviruses from Naturally Infected Sheep and Goats from Mexico

Small ruminant lentiviruses (SRLVs) belong to the genus Lentivirus in the Retroviridae family. There are five genotypes (A, B, C, D, and E), where genotypes A and B have a global distribution and genotypes C, D, and E are limited to Europe. The presence of SRLV has been confirmed in Mexico, with genotype B detected in the central region of the country. We examined the presence of SRLVs and genotype prevalence in 1014 sheep and 1383 goats from 12 Mexican states. Using a commercial competitive ELISA (cELISA) test, we detected SRLV antibodies in 107 sheep (10.55%) and 466 goats (33.69%). We used an endpoint PCR to amplify the LTR region on seropositive animals. A total of 50 sheep and 75 goats tested positive via PCR. Positive amplicons from 11 sheep and 17 goats from ten Mexican States were cloned and sequenced. With the LTR sequence data obtained in this study, a phylogenetic analysis was performed; we also constructed a phylogenetic tree using the obtained sequences and GenBank's available sequences. All studied sequences were associated with genotype B, specifically with the FESC-752 isolate previously identified in Mexico. Highly conserved transcription factor binding sites were observed in analyzed alignments, such as AML (vis), AP-4, and TATA box. However, we identified nucleotide differences at site AP-1 that suggest function loss. Our study found that ovine and caprine genotype B SRLVs are widely distributed in Mexico; a highly conserved LTR region among the sequences evaluated in this study was also found.

Genotyping Based on the LTR Region of Small Ruminant Lentiviruses from Naturally Infected Sheep and Goats from Mexico

Small ruminant lentiviruses (SRLVs) belong to the genusLentivirusin the Retroviridae family. There are five genotypes (A, B, C, D, and E), where genotypes A and B have a global distribution and genotypes C, D, and E are limited to Europe. The presence of SRLV has been confirmed in Mexico, with genotype B detected in the central region of the country. We examined the presence of SRLVs and genotype prevalence in 1014 sheep and 1383 goats from 12 Mexican states. Using a commercial competitive ELISA (cELISA) test, we detected SRLV antibodies in 107 sheep (10.55%) and 466 goats (33.69%). We used an endpoint PCR to amplify the LTR region on seropositive animals. A total of 50 sheep and 75 goats tested positive via PCR. Positive amplicons from 11 sheep and 17 goats from ten Mexican States were cloned and sequenced. With the LTR sequence data obtained in this study, a phylogenetic analysis was performed; we also constructed a phylogenetic tree using the obtained sequences and GenBank’s available sequences. All studied sequences were associated with genotype B, specifically with the FESC-752 isolate previously identified in Mexico. Highly conserved transcription factor binding sites were observed in analyzed alignments, such as AML (vis), AP-4, and TATA box. However, we identified nucleotide differences at site AP-1 that suggest function loss. Our study found that ovine and caprine genotype B SRLVs are widely distributed in Mexico; a highly conserved LTR region among the sequences evaluated in this study was also found.

Epidemiological survey in single-species flocks from Poland reveals expanded genetic and antigenic diversity of small ruminant lentiviruses

Small ruminant lentivirus (SRLV) infections are widespread in Poland and circulation of subtypes A1, A12, A13, B1 and B2 was detected. The present work aimed at extending previous study based on the analysis of a larger number of animals from single-species flocks. Animals were selected for genetic analysis based on serological reactivity towards a range of recombinant antigens derived from Gag and Env viral proteins. Phylogenetic analysis revealed the existence of subtypes B2 and A12 in both goats and sheep and subtypes A1 and B1 in goats only. In addition, two novel subtypes, A16 and A17, were found in goats. Co-infections with strains belonging to different subtypes within A and B groups were detected in 1 sheep and 4 goats originating from four flocks. Although the reactivity of serum samples towards the recombinant antigens confirmed immunological relatedness between Gag epitopes of different subtypes and the cross-reactive nature of Gag antibodies, eleven serum samples failed to react with antigens representing all subtypes detected up-to-date in Poland, highlighting the limitations of the serological diagnosis. These data showed the complex nature of SRLV subtypes circulating in sheep and goats in Poland and the need for improving SRLV-related diagnostic capacity.

Small ruminant lentivirus infections and diseases

Small ruminant lentiviruses include viruses with diverse genotypes that frequently cross the species barrier between sheep and goats and that display a great genetic variability. These characteristics stress the need to consider the whole host range and to perform local surveillance of the viruses to opt for optimum diagnostic tests, in order to establish control programmes. In the absence of effective vaccines, a comprehensive knowledge of the epidemiology of these infections is of major importance to limit their spread. This article intends to cover these aspects and to summarise information related to characteristics of the viruses, pathogenesis of the infection and description of the various syndromes produced, as well as the diagnostic tools available, the mechanisms involved in transmission of the pathogens and, finally, the control strategies that have been designed until now, with remarks on the drawbacks and the advantages of each one. We conclude that there are many variables influencing the expected cost and benefits of control programs that must be evaluated, in order to put into practice measures that might lead to control of these infections.

Generation of a molecular clone of an attenuated lentivirus, a first step in understanding cytopathogenicity and virulence

Small ruminant lentiviruses infect goats and sheep, inducing clinical disease in a minority of infected animals. Following an eradication campaign, clinical cases may disappear in a population. The complete elimination of these lentiviruses is however difficult to achieve and the spreading of less virulent strains often parallels the elimination of their virulent counterparts. Here, we characterized three such strains isolated from a flock in the post-eradication phase. We completely sequenced their genomes, showing that one of the isolates was most probably the product of a recombination event between the other two viruses. By comparing the sequences of these isolates with those of virulent strains, we found evidence that particular LTR mutations may explain their attenuated phenotype. Finally, we constructed an infectious molecular clone representative of these viruses, analyzing its replication characteristics in different target cells. This clone will permit us to explore the molecular correlates of cytopathogenicity and virulence.

Identification and characterization of an emerging small ruminant lentivirus circulating recombinant form (CRF)

The molecular epidemiology of small ruminant lentiviruses (SRLVs) is constantly changing due to animal movements, cross species transmission and because of their rapid evolutionary rate. This study reports a comprehensive genetic and phylogenetic analysis based on consensus gag and pol sequences covering 3kb of the SRLV genome from small ruminants in Québec, Canada. A group of strains obtained from goats originating from different flocks, segregated in a unique clade distinct from currently known SRLV groups. Genetic dissection of the gag gene from these strains revealed that it originated as a result of a recombination event between parental strains currently circulating in small ruminants of the country. Following HIV nomenclature, we propose to call this group of strains, circulating recombinant form 1 SRLV, or CRF01_AB SRLV. In addition, the study confirms the existence of genetically distinct and homogeneous populations of SRLVs infecting sheep and goats housed in single species flocks.

Small ruminant lentivirus-induced arthritis: clinicopathologic findings in sheep infected by a highly replicative SRLV B2 genotype

We describe the clinicopathologic features of an arthritis outbreak in sheep induced by small ruminant lentivirus (SRLV), linked to the presence of a new SRLV isolate phylogenetically assigned to caprine arthritis encephalitis virus-like subgroup B2. Thirteen SRLV seropositive Rasa Aragonesa adult ewes were selected from 5 SRLV highly infected flocks (mean seroprevalence, 90.7%) for presenting uni- or bilateral chronic arthritis in the carpal joint. A complete study was performed, including symptomatology, histopathology, immunocytochemistry, immunohistochemistry, in situ hybridization, and microbiology. The carpus was the joint almost exclusively affected, with 10 sheep (76%) showing a moderate increase in carpal joint size (diameter range, 18-20 cm; normal range, 15-16 cm) without signs of locomotion problems and with 3 ewes (23%) showing severe inflammation with marked increase in diameter (21-24 cm), pain at palpation, and abnormal standing position. Grossly, chronic proliferative arthritis was observed in affected joints characterized by an increased thickness of the synovial capsule and synovial membrane proliferation. Microscopically, synovial membrane inflammation and proliferation and hyperplasia of synoviocytes were observed. More positive cases of SLRV infection were detected by immunocytochemistry of articular fluid than of bronchoalveolar lavage fluid. Immunohistochemistry and in situ hybridization also detected positive cells in the subsynovial connective tissue, lung, mediastinal lymph node, mammary gland, and mammary lymph node. All animals were negative for the presence of Mycoplasma or other bacteria in the articular space. The present outbreak likely represents an adaptation of a caprine virus to sheep. Our results underline the importance of the arthritis induced by SRLV in sheep, a clinical form that might be underestimated.

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.

An insight into a combination of ELISA strategies to diagnose small ruminant lentivirus infections

A single broadly reactive standard ELISA is commonly applied to control small ruminant lentivirus (SRLV) spread, but type specific ELISA strategies are gaining interest in areas with highly prevalent and heterogeneous SRLV infections. Short (15-residue) synthetic peptides (n=60) were designed in this study using deduced amino acid sequence profiles of SRLV circulating in sheep from North Central Spain and SRLV described previously. The corresponding ELISAs and two standard ELISAs were employed to analyze sera from sheep flocks either controlled or infected with different SRLV genotypes. Two outbreaks, showing SRLV-induced arthritis (genotype B2) and encephalitis (genotype A), were represented among the infected flocks. The ELISA results revealed that none of the assays detected all the infected animals in the global population analyzed, the assay performance varying according to the genetic type of the strain circulating in the area and the test antigen. Five of the six highly reactive (57-62%) single peptide ELISAs were further assessed, revealing that the ELISA based on peptide 98M (type A ENV-SU5, consensus from the neurological outbreak) detected positives in the majority of the type-A specific sera tested (Se: 86%; Sp: 98%) and not in the arthritic type B outbreak. ENV-TM ELISAs based on peptides 126M1 (Se: 82%; Sp: 95%) and 126M2 0,65 0.77 (Se: 68%; Sp: 88%) detected preferentially caprine arthritis encephalitis (CAEV, type B) and visna/maedi (VMV, type A) virus infections respectively, which may help to perform a preliminary CAEV vs. VMV-like typing of the flock. The use of particular peptide ELISAs and standard tests individually or combined may be useful in the different areas under study, to determine disease progression, diagnose/type infection and prevent its spread.

Quantitative estimation of the impact of caprine arthritis encephalitis virus infection on milk production by dairy goats

This retrospective study investigated milk production losses associated with serological evidence (serostatus) of caprine arthritis encephalitis virus (CAEV) infection over one lactation in 4543 Murciano-Granadina goats from 22 herds in Spain. The seroprevalence of infection was 18%, ranging from 0% to 2% in 11 herds, 7% to 60% in 10 herds and was 100% in one herd. Seropositive does had significantly shorter lactations, produced less milk and milk fat, lactose and dry extract and had higher somatic cell counts than their seronegative counterparts, although differences in milk production between seropositive and seronegative animals were noted between herds. Mixed regression models confirmed the association between CAEV seropositivity and reduced milk production. The adjusted, least squares mean (LSM) test-day milk yield was 10% less in seropositive compared to seronegative does and this difference varied according to lactation number. In contrast, differences in the LSM of milk fat, lactose and dry extract percentages between seropositive and seronegative goats were only between 0.1% and 0.2% and did not increase with lactation number. The findings of this study provide strong evidence that CAEV-infection can be a major cause of reduction in milk yield in goats and its control should be considered as part of dairy goat herd health schemes.

Diversity of caprine arthritis-encephalitis virus promoters isolated from goat milk and passaged in vitro

Transcriptional regulation in retroviruses resides in the U3 region of the proviral long terminal repeat (LTR). Transcription binding sites (TBS) in the U3 region of proviral sequences derived from the milk of 17 goats infected with caprine arthritis-encephalitis virus (CAEV) were analysed by nested PCR and sequencing. U3 sequences shared a high degree of homology (86-99%) and were closely related to isolates previously ascribed to small ruminant lentivirus subtype B1. Multiple putative AP-1, AP-4, Ets-1, Stat-1 and TATA binding protein (TBP) sites were highly conserved (>85% of isolates), as were single AML(vis), GAS, IRF-1, NFAT and TAS sites. A 10 nucleotide insertion of undetermined relevance was identified in the U3 region of two isolates. To study the stability of TBS within the CAEV U3 region through in vitro passage, milk-derived isolates of CAEV from three infected dams were cultured in goat synovial membrane (GSM) cells; in one isolate the viral U3 region was completely stable during in vitro passage, in a second isolate the viral U3 region accumulated multiple deletions, single nucleotide polymorphisms and insertions, while a third isolate had an intermediate degree of promoter stability. Promoter mutations arising during in vitro passage did not affect most of the conserved putative TBS identified in CAEV.