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

Comparison of serological and molecular methods for differentiation between genotype A and genotype B strains of small ruminant lentiviruses

Introduction

Small ruminant lentiviruses (SRLV) cause multisystemic, degenerative and chronic disease in sheep and goats. There are five genotypes (A, B, C, D and E), of which A and B are the most widespread. The purpose of this study was to evaluate the serotyping efficiency of the Eradikit SRLV Genotyping ELISA and the molecular typing efficiency of a newly developed nested real-time PCR targeting the long terminal repeat-gag (LTR-gag) region using samples from animals infected with subtypes of SRLV known to circulate in Poland.

Material and Methods

A total of 97 sera samples taken from 34 sheep and 63 goats were immunoassayed, and 86 DNA samples from 31 sheep and 55 goats were tested with the PCR. All ruminants were infected with known SRLV strains of the A1, A5, A12, A13, A16, A17, A18, A23, A24, A27, B1 and B2 subtypes.

Results

A total of 69 (80.2%, 95% confidence interval 71.6%-88.8%) out of 86 tested samples gave positive results in the PCR. In 17 out of the 86 (19.8%) samples, no proviral DNA of SRLV was detected. The differentiation between MVV (genotype A) and CAEV (genotype B) by PCR matched the predating phylogenetic analysis invariably. No cross-reactivity was observed. On the other hand, the proportion of samples genotyped the same by the older phylogenetic analysis and the Eradikit SRLV Genotyping ELISA was 42.3%. The test was unable to classify 40.2% of samples, and 17.5% of sera were incorrectly classified.

Conclusion

Our results showed that the Eradikit SRLV genotyping kit is not a reliable method for predicting SRLV genotype, while the nested real-time PCR based on the LTR-gag region did prove to be, at least for genotypes A and B.

A Combined Approach for the Characterization of Small Ruminant Lentivirus Strains Circulating in the Islands and Mainland of Greece

Small ruminant lentiviruses are a group of viruses infecting goat and sheep worldwide. These viruses exhibit an extraordinary degree of genetic and antigenic variability that severely influence in vivo and in vitro features, as well as diagnostic test results. Small ruminant farming is the most important animal farming business in Greece, with a high impact on the Greek primary economy. Although SRLV infection and its impact on animal production are well established in the country, little is known about the circulating SRLV strains and their prevalence. The aim of this study was to characterize SRLVs circulating in Greece with a combined serological and molecular approach, using the bulk milk matrix collected from 60 farms in different municipalities. This study allowed us to estimate a seroprevalence of around 52% at the herd level. The B1, B2 and A3 subtypes and a novel A viral cluster were identified. Moreover, the amplicon sequencing method allowed us to identify more than one viral subtype in a sample. These results again confirm the high variability of these viruses and highlight the importance of the constant monitoring of viral evolution, in particular in antigens of diagnostic interest.

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.

A Combined Approach for Detection of Ovine Small Ruminant Retrovirus Co-Infections

Jaagsiekte retrovirus (JSRV)-induced ovine pulmonary adenocarcinoma (OPA) is an important ovine respiratory disease in Switzerland. Furthermore, ovine lungs with OPA frequently exhibited lesions suggestive of maedi-visna virus (MVV) or caprine arthritis encephalitis virus (CAEV) infection, indicating that co-morbidities might occur. Lungs and pulmonary lymph nodes were sampled from suspected OPA cases, inflammatory lung lesions and control lungs (total of 110 cases). Tissues were (a) processed for histology and immunohistochemistry (IHC), and (b) underwent DNA extraction and real-time PCR for JSRV, MVV and CAEV. Peptide sequences were used to generate virus-specific customized polyclonal antibodies. PCR-positive OPA cases and formalin-fixed and paraffin-embedded MVV- and CAEV-infected synovial cell pellets served as positive controls. Fifty-two lungs were histologically diagnosed with OPA. Histological evidence of MVV/CAEV infection was detected in 25 lungs. JSRV was detected by PCR in 84% of the suspected OPA cases; six were co-infected with MVV and one with CAEV. MVV was detected by PCR in 14 cases, and four lungs were positive for CAEV. Three lungs had MVV/CAEV co-infection. In IHC, JSRV was detected in 91% of the PCR-positive cases, whereas MVV and CAEV immunoreactivity was seen in all PCR-positive lungs. Although PCR showed a higher sensitivity compared to IHC, the combined approach allows for investigations on viral cell tropism and pathogenic processes in co-morbidities, including their potential interdependency. Furthermore, an immunohistochemical tool for specific differentiation of MVV and/or CAEV infection was implemented.

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.

Evaluation of Serological Methods and a New Real-Time Nested PCR for Small Ruminant Lentiviruses

Small ruminant lentiviruses (SRLVs), i.e., CAEV and MVV, cause insidious infections with life-long persistence and a slowly progressive disease, impairing both animal welfare and productivity in affected herds. The complex diagnosis of SRLVs currently combines serological methods including whole-virus and peptide-based ELISAs and Immunoblot. To improve the current diagnostic protocol, we analyzed 290 sera of animals originating from different European countries in parallel with three commercial screening ELISAs, Immunoblot as a confirmatory assay and five SU5 peptide ELISAs for genotype differentiation. A newly developed nested real-time PCR was carried out for the detection and genotype differentiation of the virus. Using a heat-map display of the combined results, the drawbacks of the current techniques were graphically visualized and quantified. The immunoblot and the SU5-ELISAs exhibited either unsatisfactory sensitivity or insufficient reliability in the differentiation of the causative viral genotype, respectively. The new truth standard was the concordance of the results of two out of three screening ELISAs and the PCR results for serologically false negative samples along with genotype differentiation. Whole-virus antigen-based ELISA showed the highest sensitivity (92.2%) and specificity (98.9%) among the screening tests, whereas PCR exhibited a sensitivity of 75%.

First molecular detection of Maedi-Visna virus in Awassi sheep of Middle Iraq regions

Respiratory viral infections cause significant economic losses in sheep production. This preliminary molecular study aimed to detect the Maedi-Visna virus infection in Awassi sheep in three governorates in the middle region of Iraq. The presence of one or more of the specific four genes (gag, pol, env and LTR) were considered as positive result. A total of 210 blood samples of Awassi sheep were collected for the purpose of the project. The molecular prevalence of Maedi-Visna virus in sheep was 12.85% (27/210). As a result, Maedi-Visna virus was observed in sheep with chronic respiratory system disease with non-significant difference between governorates and between primers percentage (P>0.05). Sequencing studies strongly suggested that Maedi-Visna virus originated in Iraq. This is the first study describing Iraqi Maedi-Visna virus sequences with molecular characterisation of gag, pol, env and LTR genes, suggesting that Maedi-Visna virus originated in Iraq.

Species-Specific Humoral Immune Responses in Sheep and Goats upon Small Ruminant Lentivirus Infections Inversely Correlate with Protection against Virus Replication and Pathological Lesions

Maedi-Visna-like genotype A strains and Caprine arthritis encephaltis-like genotype B strains are small ruminant lentiviruses (SRLV) which, for incompletely understood reasons, appear to be more virulent in sheep and goats, respectively. A 9-month in vivo infection experiment using Belgian genotype A and B SRLV strains showed that almost all homologous (genotype A in sheep; genotype B in goats) and heterologous (genotype A in goats; genotype B in sheep) intratracheal inoculations resulted in productive infection. No differences in viremia and time to seroconversion were observed between homologous and heterologous infections. Higher viral loads and more severe lesions in the mammary gland and lung were however detected at 9 months post homologous compared to heterologous infection which coincided with strongly increased IFN-γ mRNA expression levels upon homologous infection. Pepscan analysis revealed a strong antibody response against immune-dominant regions of the capsid and surface proteins upon homologous infection, which was absent after heterologous infection. These results inversely correlated with protection against virus replication in target organs and observed histopathological lesions, and thus require an in-depth evaluation of a potential role of antibody dependent enhancement in SRLV infection. Finally, no horizontal intra- and cross-species SRLV transmission to contact animals was detected.

Serological, Molecular and Culture-Based Diagnosis of Lentiviral Infections in Small Ruminants

Small ruminant lentiviruses (SRLVs) infections lead to chronic diseases and remarkable economic losses undermining health and welfare of animals and the sustainability of farms. Early and definite diagnosis of SRLVs infections is the cornerstone for any control and eradication efforts; however, a "gold standard" test and/or diagnostic protocols with extensive applicability have yet to be developed. The main challenges preventing the development of a universally accepted diagnostic tool with sufficient sensitivity, specificity, and accuracy to be integrated in SRLVs control programs are the genetic variability of SRLVs associated with mutations, recombination, and cross-species transmission and the peculiarities of small ruminants' humoral immune response regarding late seroconversion, as well as intermittent and epitope-specific antibody production. The objectives of this review paper were to summarize the available serological and molecular assays for the diagnosis of SRLVs, to highlight their diagnostic performance emphasizing on advantages and drawbacks of their application, and to discuss current and future perspectives, challenges, limitations and impacts regarding the development of reliable and efficient tools for the diagnosis of SRLVs infections.

Maedi-Visna virus: current perspectives

Maedi-Visna virus (MVV) and caprine arthritis-encephalitis virus are commonly known as small ruminant lentiviruses (SRLVs) due to their genetic, structural, and pathogenic similarities. They produce lifelong lasting infections in their hosts, which are characterized by slow progression till overt disease happens. There are four major clinical forms derived from a chronic inflammatory response due to the constant low grade production of viruses from monocyte-derived macrophages: respiratory (caused by interstitial pneumonia), mammary (which may produce a decrease in milk production due to subclinical mastitis), joint (characterized by lameness), and neurological (characterized by chronic nonpurulent meningoencephalomyelitis). There are three levels which try to eliminate the virus: cellular, body, and the flock level. However, SRLVs have ways to counteract these defenses. This review examines some of them.

Genetic characterisation of small ruminant lentiviruses in sheep and goats from the Czech Republic

The aim of this study was to determine the prevalence of small ruminant lentivirus (SRLV) infections on sheep and goat farms which are exempt from state monitoring and carry molecular characterisation of strains circulating amongst these farms without SRLV eradication. A total number of 3,410 blood samples of sheep and goats from 21 herds were collected for the purpose of the project. The detected serological prevalence of maedi visna in sheep was 19.9% (556/2801) and the seroprevalence of caprine arthritis and encephalitis in goats was 14.1% (86/609). All positive animals were tested by the nested polymerase chain reaction (nPCR) method for the presence of provirus in the buffy-coats from EDTA-blood samples. Phylogenetic analysis of 93 SRLV strains identified the genotype in 77 sequences, where 60 of them were genotype A and 17 belonged to genotype B. Whereas all of the genotype B sequences were classified in subtype B2, the genotype A group of isolates showed higher variability and were related to subgenotypes A2 and A3. This study represents the first report of genetic characterisation of SRLV strains circulating in the territory of the Czech Republic.

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 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.

Diverse host–virus interactions following caprine arthritis-encephalitis virus infection in sheep and goats

Interspecies transmissions substantially contribute to the epidemiology of small ruminant lentiviruses (SRLVs), including caprine arthritis encephalitis virus (CAEV) and visna-maëdi virus. However, comprehensive studies of host–virus interactions during SRLV adaptation to the new host are lacking. In this study, virological and serological features were analysed over a 6 month period in five sheep and three goats experimentally infected with a CAEV strain. Provirus load at the early stage of infection was significantly higher in sheep than in goats. A broad antibody reactivity against the matrix and capsid proteins was detected in goats, whereas the response to these antigens was mostly type-specific in sheep. The humoral response to the major immunodominant domain of the surface unit glycoprotein was type-specific, regardless of the host species. These species-specific immune responses were then confirmed in naturally infected sheep and goats using sera from mixed flocks in which interspecies transmissions were reported. Taken together, these results provide evidence that SRLV infections evolve in a host-dependent manner, with distinct host–virus interactions in sheep and goats, and highlight the need to consider both SRLV genotypes in diagnosis, particularly in sheep.

Genetic and antigenic characterization of small ruminant lentiviruses circulating in Poland

Small ruminant lentivirus (SRLV) infections are widespread in Poland, but the genetic features of sheep viruses are still lacking and limited to partial gag sequences for goat viruses. In this study, segments from the gag and env genes of Polish SRLV strains screened by heteroduplex mobility assay were subjected to genetic analyses. Subtype A1 was found in both sheep and goats, while subtypes B1 and B2 were found in goats and sheep, respectively. In addition, two novel subtypes (named A12 and A13) were found in sheep. Their close phylogenetic relatedness with SRLV strains previously isolated from Polish goats indicated that these new subtypes are predominant and circulate in both species. The antigenic relationships of subtypes A12 and A13 with other SRLV subtypes were tested in an ELISA assay based on recombinant antigens carrying the immunodominant domains of structural proteins (MA, CA and SU). Antigenic cross-reactivity in the Gag epitopes was evident among genotype A subtypes and, to a lower extent, between genotypes A and B. In contrast, a subtype-specific immunoresponse was detected in the SU epitopes. These results emphasize the broad genetic and antigenic diversity of SRLV strains circulating in Europe and confirmed the need to consider all viral genotypes to choose the antigens in serological tests in order to avoid misdiagnosis in control and eradication programs.

Characterization of new small ruminant lentivirus subtype B3 suggests animal trade within the Mediterranean Basin

Small ruminant lentiviruses (SRLVs) represent a group of viruses infecting sheep and goats worldwide. Despite the high heterogeneity of genotype A strains, which cluster into as many as ten subtypes, genotype B was believed to be less complex and has, so far, been subdivided into only two subtypes. Here, we describe two novel full-length proviral sequences isolated from Sarda sheep in two Italian regions. Genome sequence as well as the main linear epitopes clearly placed this cluster into genotype B. However, owing to long-standing segregation of this sheep breed, the genetic distances that are clearly >15 % with respect to B1 and B2 subtypes suggest the designation of a novel subtype, B3. Moreover the close relationship with a gag sequence obtained from a Turkish sheep adds new evidence to historical data that suggest an anthropochorous dissemination of hosts (small ruminants) and their pathogens (SRLV) during the colonization of the Mediterranean from the Middle East.

Field evaluation of a gag/env heteroduplex mobility assay for genetic subtyping of small-ruminant lentiviruses

Small-ruminant lentiviruses (SRLVs) display a high genetic diversity and are currently classified into five genotypes and an increasing number of subtypes. The co-circulation of subtypes in restricted geographical regions, combined with the occurrence of cross-species infection, suggests the need for development of a large-scale screening methodology for rapid monitoring of the prevalence of the various genetic subtypes and their genetic evolution. Here, a heteroduplex mobility assay (HMA) was developed for the rapid identification of group B subtypes. The assay was validated for both the p14 nucleocapsid-coding region of the gag gene and the V1-V2 region of the env gene using a panel of reference standards and was applied to the genetic subtyping of SRLV field isolates from five mixed flocks in France. Subtyping of 75 blood samples using the env HMA revealed a preferential distribution of subtypes B1 and B2 in sheep and goats, despite direct evidence for interspecies transmission of both subtypes. Adding the gag HMA to the env HMA provided evidence for dual infection and putative recombination between subtypes B1 and B2 in five goats, and between groups A and B in one sheep. Phylogenetic analysis revealed that 100 % (23/23) and 96.7 % (30/31) of samples were correctly classified using the gag and env HMAs, respectively. These results indicate that dual infection and recombination may be a significant source of new variation in SRLV and provide a useful tool for the rapid genetic subtyping of SRLV isolates, which could be relevant for the development of more accurate diagnosis of prevalent SRLV strains in different countries.

Demonstration of coinfection with and recombination by caprine arthritis-encephalitis virus and maedi-visna virus in naturally infected goats

Recombination of different strains and subtypes is a hallmark of lentivirus infections, particularly for human immunodeficiency virus, and contributes significantly to viral diversity and evolution both within individual hosts and within populations. Recombinant viruses are generated in individuals coinfected or superinfected with more than one lentiviral strain or subtype. This, however, has never been described in vivo for the prototype lentivirus maedi-visna virus of sheep and its closely related caprine counterpart, the caprine arthritis-encephalitis virus. Cross-species infections occur in animals living under natural conditions, which suggests that dual infections with small-ruminant lentiviruses (SRLVs) are possible. In this paper we describe the first documented case of coinfection and viral recombination in two naturally infected goats. DNA fragments encompassing a variable region of the envelope glycoprotein were obtained from these two animals by end-limiting dilution PCR of peripheral blood mononuclear cells or infected cocultures. Genetic analyses, including nucleotide sequencing and heteroduplex mobility assays, showed that these goats harbored two distinct populations of SRLVs. Phylogenetic analysis permitted us to assign these sequences to the maedi-visna virus group (SRLV group A) or the caprine arthritis-encephalitis virus group (SRLV group B). SimPlot analysis showed clear evidence of A/B recombination within the env gene segment of a virus detected in one of the two goats. This case provides conclusive evidence that coinfection by different strains of SRLVs of groups A and B can indeed occur and that these viruses actually recombine in vivo.