Restrictive type of replication of ovine/caprine lentiviruses in ovine fibroblast cell cultures

Productive Replication of HIV-1 but Not SIVmac in Small Ruminant Cells

Animal lentiviruses (LVs) have been proven to have the capacity to cross the species barrier, to adapt in the new hosts, and to increase their pathogenesis, therefore leading to the emergence of threatening diseases. However, their potential for widespread diffusion is limited by restrictive cellular factors that block viral replication in the cells of many species. In previous studies, we demonstrated that the restriction of CAEV infection of sheep choroid plexus cells was due to aberrant post-translation cleavage of the CAEV Env gp170 precursor. Later, we showed that the lack of specific receptor(s) for caprine encephalitis arthritis virus (CAEV) on the surface of human cells was the only barrier to their infection. Here, we examined whether small ruminant (SR) cells can support the replication of primate LVs. Three sheep and goat cell lines were inoculated with cell-free HIV-1 and SIVmac viral stocks or transfected with infectious molecular clone DNAs of these viruses. The two recombinant lentiviral clones contained the green fluorescent protein (GFP) reporter sequence. Infection was detected by GFP expression in target cells, and the infectious virus produced and released in the culture medium of treated cells was detected using the indicator TZM-bl cell line. Pseudotyped HIV-GFP and SIV-GFP with vesicular stomatitis virus G glycoprotein (VSV-G) allowed the cell receptors to be overcome for virus entry to further evaluate the viral replication/restriction in SR cells. As expected, neither HIV nor SIV viruses infected any of the SR cells. In contrast, the transfection of plasmid DNAs of the infectious molecular clones of both viruses in SR cells produced high titers of infectious viruses for human indicators, but not SR cell lines. Surprisingly, SR cells inoculated with HIV-GFP/VSV-G, but not SIV-GFP/VSV-G, expressed the GFP and produced a virus that efficiently infected the human indictor, but not the SR cells. Collectively, these data provide a demonstration of the lack of replication of the SIVmac genome in SR cells, while, in contrast, there was no restriction on the replication of the IV-1 genome in these cells. However, because of the lack of functional receptors to SIVmac and HIV-1 at the surface of SR cells, there is specific lentiviral entry.

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.

Foot and mouth disease virus undergoes non-progressive replication in mice peritoneal macrophages and induces M1 polarization

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Non-progressive replication of foot and mouth disease virus was observed in mice peritoneal macrophages.

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Macrophages turns to M1 type polarization in response to FMDV infection.

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Upregulation of pro-inflammatory cytokines was peak by 8 h FMDV infection.

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Type I IFN and viperin showed marked upregulation following FMDV infection in the macrophages.

Despite the fact that macrophages link the innate and adaptive arms of immunity, it’s role in the early infection of foot and mouth disease virus (FMDV) is largely unknown. Recently, depletion of macrophages in vivo after vaccination has shown to drastically diminish the protection against FMDV challenge in mouse model. Even the ability of macrophages to reduce or resist FMDV infection is not known hitherto. Therefore, we examined the replication ability of FMDV in mice peritoneal macrophages and the responsiveness in terms of macrophage polarization and cytokine production. Negative strand specific RT-PCR indicated replication of FMDV RNA in macrophages. Absolute quantitation of FMDV transcripts, immunofluorescence studies and titre of the infectious progeny virus revealed that replication peaked at 12 hpi and significantly declined by 18 hpi indicating non-progressive replication in the infected macrophages. Further, significant up regulation of inducible nitric oxide synthase by 8 –12 hpi and increase of M1 specific CD11c + cells by 42.6 % after infection showed that FMDV induce M1 polarization. A significant up regulation of TNFα and IL12 transcripts at 8 hpi supported that M1 macrophages were functional. Further, we studied the expression of Type I to III interferons (IFN) and other antiviral molecules. The results indicate a marked up regulation of Type I IFNα and β by 9.2 and 11.2 fold, respectively at 8 hpi. Of the four IFN stimulated genes (ISG), viperin showed a significant up regulation by 286-fold at 12 hpi in the mice macrophages. In conclusion, the results suggest that replication of FMDV in mice peritoneal macrophages is non-progressive with up regulation of Type I IFN and ISGs. Further, FMDV induces M1 polarization in murine peritoneal macrophages.

An Immunodominant Region of the Envelope Glycoprotein of Small Ruminant Lentiviruses May Function as Decoy Antigen

(1) Background: Small ruminant lentiviruses (SRLV) persist in infected goats that mount a strong humoral immune response characterized by low neutralizing titers. In this study, we characterized the antibody response to SU5, a variable, immunodominant epitope of the envelope glycoprotein of SRLV. We tested the working hypothesis that the variability of SU5 reflects escape from neutralizing antibody. (2) Methods: Affinity purified anti-SU5 antibody were tested for their neutralizing activity to the homologous lentivirus. Virus culture supernatant—in native form or following sonication and filtration—was used to test the ability of free envelope glycoproteins to compete for binding in a SU5-peptide-ELISA. (3) Results: Anti-SU5 antibodies are not neutralizing, strongly suggesting that they do not bind intact viral particles. In contrast, shed envelope glycoproteins efficiently compete for binding in a SU5-ELISA, providing convincing evidence that the SU5 epitope is exposed only on shed envelope glycoproteins. (4) Conclusions: Our results show that the antibody engaging SU5 is not neutralizing and does not appear to bind to SU expressed at the surface of virus particles. We propose that SU5 is a potential decoy epitope exposed on shaded envelope glycoproteins, luring the humoral immune response in committing an original antigenic sin to a functionally irrelevant epitope.

Immortalized sheep microglial cells are permissive to a diverse range of ruminant viruses

BACKGROUND

Ruminants, including sheep and goats (small ruminants), are key agricultural animals in many parts of the world. Infectious diseases, including many viral diseases, are significant problems to efficient production of ruminants. Unfortunately, reagents tailored to viruses of ruminants, and especially small ruminants, are lacking compared to other animals more typically used for biomedical research.

OBJECTIVE

The purpose of this study was to determine the permissibility of a stably immortalized, sheep microglial cell line to viruses that are reported to infect ruminants: bovine viral diarrhea virus (BVDV), bovine herpesvirus 1 (BoHV-1), small ruminant lentiviruses (SRLV), and bovine respiratory syncytial virus (BRSV).

METHODS

Sublines A and H of previously isolated, immortalized, and characterized (CD14-positive) ovine microglial cells were used. Bovine turbinate cells and goat synovial membrane cells were used for comparison. Cytopathic changes were used to confirm infection of individual wells, which were then counted and used to calculate the 50% tissue culture infectious dose. Uninoculated cells served as negative controls and confirmed that the cells were not previously infected with these viruses using polymerase chain reaction (PCR).

RESULTS

Inoculation of the two microglial cell sublines with laboratory and field isolates of BVDV, BoHV-1, and BRSV resulted in viral infection in a manner similar to bovine turbinate cells. Immortalized microglia cells are also permissive to SRLV, similar to goat synovial membrane cells.

CONCLUSION AND CLINICAL RELEVANCE

These immortalized sheep microglial cells provide a new tool for the study of ruminant viruses in ruminant microglial cell line.

Goat umbilical cord cells are permissive to small ruminant lentivirus infection in vitro

Small ruminant lentiviruses isolated from peripheral blood leukocytes and target organs can be propagated in vitro in fibroblasts derived from goat synovial membrane cells. These cells are obtained from tissues collected from embryos or fetuses and are necessary for the establishment of the fibroblast primary culture. A new alternative type of host cells, derived from goat umbilical cord, was isolated and characterized phenotypically with its main purpose being to obtain cell monolayers that could be used for the diagnosis and isolation of small ruminant lentiviruses in cell culture. To accomplish this goal, cells were isolated from umbilical cords; characterized phenotypically by flow cytometry analysis; differentiate into osteogenic, chondrogenic and adipogenic lineage; and submitted to viral challenge. The proliferation of goat umbilical cord cells was fast and cell monolayers formed after 15 days. These cells exhibited morphology, immunophenotype, growth characteristics, and lineage differentiation potential similar to mesenchymal stem cells of other origins. The goat umbilical cord derived cells stained positive for vimentin and CD90, but negative for cytokeratin, CD34 and CD105 markers. Syncytia and cell lysis were observed in cell monolayers infected by CAEV-Cork and MVV-K1514, showing that the cells are permissive to small ruminant lentivirus infection in vitro. These data demonstrate the proliferative competence of cells derived from goat umbilical cords and provide a sound basis for future research to standardize this cell lineage.

Low proviral small ruminant lentivirus load as biomarker of natural restriction in goats

Small ruminant lentiviruses (SRLV) globally affect welfare and production of sheep and goats and are mainly controlled through elimination of infected animals, independently of the viral kinetics within the single animal. Control programs are based on highly sensitive serological tests, however the existence of low antibody responders leads to the permanent presence of seronegative infected animals in the flock, thus perpetuating the infection. On the other hand, long-term non-progressors show a detectable antibody response not indicative of a shedding animal, suggesting immune contention of infection. In this study, we analyse two goat populations within the same herd, harbouring low or high proviral SRLV loads respectively, both showing a robust antibody response. In vivo findings were confirmed in vitro since fibroblastic cell lines obtained from one high and one low proviral load representative goats, showed respectively a high and a faint production of virus upon infection with reference and field circulating SRLV strains. Differences in virus production were relieved when strain CAEV-Co was used for experimental infection. We analysed LTR promoter activity, proviral load, entry step and production of virus and viral proteins. Intriguingly, proteasomal activity was higher in fibroblasts from low proviral load animals and proteasome inhibition increased viral production in both cell lines, suggesting the implication of active proteasome-dependent restriction factors. Among them, we analysed relative expression and sequences of TRIM5α, APOBEC3 (Z1, Z2, Z3 and Z2-Z3) and BST-2 (Tetherin) and found a global antiviral status in low proviral carriers that may confer protection against viral shedding and disease onset.

Detailed analysis of the promoter activity of an attenuated lentivirus

In spite of an eradication campaign that eliminated clinical cases of caprine arthritis encephalitis virus-induced arthritis in the Swiss goat population, seroconversions are still observed. In the affected flocks, viruses belonging mainly to the small ruminant lentivirus A4 subtype are regularly isolated. These viruses are considered attenuated, except in the mammary gland, where high viral loads and histopathological lesions have been observed. We previously characterized and sequenced such field isolates, detecting several potentially attenuating mutations in their LTR. Here we present a detailed analysis of the promoter activity of these genetic elements, which was comparable to those of virulent isolates. An AP-1 binding site was shown to be crucial for promoter activity in reporter gene assays and also in the context of a replicating molecular clone. Other sites, such as AML(vis) and a conserved E-box, appeared to be less crucial. Analysis of a unique AP-4 site showed a clear discrepancy between results obtained with reporter gene assays and those with mutated viruses. Within the limits of this in vitro study, we did not find evidence pointing to the LTR as the genetic correlate of attenuation for these viruses. Finally, the limited replication of SRLV A4 in mammary cell culture could not explain the suggested mammary tropism. In contrast, and in view of the abundance of macrophages in the mammary gland, it is the striking replication capacity of SRLV A4 in these cells, unaffected by all LTR mutations tested, which may explain the apparent mammary tropism of these viruses.

Post-entry blockade of small ruminant lentiviruses by wild ruminants

Small ruminant lentivirus (SRLV) infection causes losses in the small ruminant industry due to reduced animal production and increased replacement rates. Infection of wild ruminants in close contact with infected domestic animals has been proposed to play a role in SRLV epidemiology, but studies are limited and mostly involve hybrids between wild and domestic animals. In this study, SRLV seropositive red deer, roe deer and mouflon were detected through modified ELISA tests, but virus was not successfully amplified using a set of different PCRs. Apparent restriction of SRLV infection in cervids was not related to the presence of neutralizing antibodies. In vitro cultured skin fibroblastic cells from red deer and fallow deer were permissive to the SRLV entry and integration, but produced low quantities of virus. SRLV got rapidly adapted in vitro to blood-derived macrophages and skin fibroblastic cells from red deer but not from fallow deer. Thus, although direct detection of virus was not successfully achieved in vivo, these findings show the potential susceptibility of wild ruminants to SRLV infection in the case of red deer and, on the other hand, an in vivo SRLV restriction in fallow deer. Altogether these results may highlight the importance of surveilling and controlling SRLV infection in domestic as well as in wild ruminants sharing pasture areas, and may provide new natural tools to control SRLV spread in sheep and goats.

Characterization of small ruminant lentivirus A4 subtype isolates and assessment of their pathogenic potential in naturally infected goats

Background

Small ruminant lentiviruses escaping efficient serological detection are still circulating in Swiss goats in spite of a long eradication campaign that essentially eliminated clinical cases of caprine arthritis encephalitis in the country. This strongly suggests that the circulating viruses are avirulent for goats.

To test this hypothesis, we isolated circulating viruses from naturally infected animals and tested the in vitro and in vivo characteristics of these field isolates.

Methods

Viruses were isolated from primary macrophage cultures. The presence of lentiviruses in the culture supernatants was monitored by reverse transcriptase assay. Isolates were passaged in different cells and their cytopathogenic effects monitored by microscopy. Proviral load was quantified by real-time PCR using customized primer and probes. Statistical analysis comprised Analysis of Variance and Bonferroni Multiple Comparison Test.

Results

The isolated viruses belonged to the small ruminant lentiviruses A4 subtype that appears to be prominent in Switzerland. The 4 isolates replicated very efficiently in macrophages, displaying heterogeneous phenotypes, with two isolates showing a pronounced cytopathogenicity for these cells. By contrast, all 4 isolates had a poor replication capacity in goat and sheep fibroblasts. The proviral loads in the peripheral blood and, in particular, in the mammary gland were surprisingly high compared to previous observations. Nevertheless, these viruses appear to be of low virulence for goats except for the mammary gland were histopathological changes were observed.

Conclusions

Small ruminant lentiviruses continue to circulate in Switzerland despite a long and expensive caprine arthritis encephalitis virus eradication campaign. We isolated 4 of these lentiviruses and confirmed their phylogenetic association with the prominent A4 subtype. The pathological and histopathological analysis of the infected animals supported the hypothesis that these A4 viruses are of low pathogenicity for goats, with, however, a caveat about the potentially detrimental effects on the mammary gland. Moreover, the high proviral load detected indicates that the immune system of the animals cannot control the infection and this, combined with the phenotypic plasticity observed in vitro, strongly argues in favour of a continuous and precise monitoring of these SRLV to avoid the risk of jeopardizing a long eradication campaign.

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.

Is caprine arthritis encephalitis virus (CAEV) transmitted vertically to early embryo development stages (morulae or blastocyst) via in vitro infected frozen semen?

The aim of this study was to determine, in vivo, whether in vitro infected cryopreserved caprine sperm is capable of transmitting caprine arthritis-encephalitis virus (CAEV) vertically to early embryo development stages via artificial insemination with in vitro infected semen. Sperm was collected from CAEV-free bucks by electroejaculation. Half of each ejaculate was inoculated with CAEV-pBSCA at a viral concentration of 10(4) TCID(50)/mL. The second half of each ejaculate was used as a negative control. The semen was then frozen. On Day 13 of superovulation treatment, 14 CAEV-free does were inseminated directly into the uterus under endoscopic control with thawed infected semen. Six CAEV-free does, used as a negative control, were inseminated intrauterine with thawed CAEV-free sperm, and eight CAEV-free does were mated with naturally infected bucks. Polymerase chain reaction (PCR) was used to detect CAEV proviral-DNA in the embryos at the D7 stage, in the embryo washing media, and in the uterine secretions of recipient does. At Day 7, all the harvested embryos were PCR-negative for CAEV proviral-DNA; however, CAEV proviral-DNA was detected in 8/14 uterine smears, and 9/14 flushing media taken from does inseminated with infected sperm, and in 1/8 uterine swabs taken from the does mated with infected bucks. The results of this study confirm that (i) artificial insemination with infected semen or mating with infected bucks may result in the transmission of CAEV to the does genital tack seven days after insemination, and (ii) irrespective of the medical status of the semen or the recipient doe, it is possible to obtain CAEV-free early embryos usable for embryo transfer.

Non-maternal transmission is the major mode of ovine lentivirus transmission in a ewe flock: a molecular epidemiology study

Transmission of ovine progressive pneumonia virus (OPPV), a lentivirus of sheep, occurs through both maternal and non-maternal means. Currently, the contribution of each route to the overall flock OPPV prevalence is poorly understood since previous serological epidemiologic studies lacked the ability to accurately track routes of transmission within an infected flock. In this study, the amount of maternal OPP transmission was assessed in a naturally infected ewe flock by applying molecular analyses to proviral sequences derived from peripheral blood leukocytes of OPP positive dam-daughter pairs (N=40). Both proviral envelope (env) and long terminal repeat (LTR) sequences, separately and combined, were utilized in the following 2 sequence analysis methods: phylogenetic analysis and pairwise distance calculations. True maternal transmission events were defined as agreement in 2 out of the 2 sequence analysis methods. Using this criterion, proviral env sequences resulted in a 14.3% maternal transmission frequency, and proviral LTR sequences resulted in a 10% maternal transmission frequency. Both proportions of maternal transmission varied significantly from equality (P<0.0001). This indicates that the remaining 85.7-90% of daughters are infected via non-maternal transmission. This is also the first study to calculate the OPP proviral rate of change for the env gene and LTR promoter. Accurately defining the routes of OPPV transmission provides critical epidemiological data supporting management intended to reduce flock transmission and viral dose.

Development and comparison of strain specific gag and pol real-time PCR assays for the detection of Visna/maedi virus

The aim of this study was the development of gag and pol dual labelled probe real-time PCR and RT PCR assays to quantify the proviral load and the transcripts of the British Visna/maedi virus EV1 strain. Primers and probes were chosen based on the consensus sequences of gag and pol clones representative of EV1 genetic variants. Both PCRs had a detection limit of 3 copies of target gene, with a linearity over 6 orders of magnitude. The performances of the two PCRs in vivo were evaluated and compared on a panel of DNAs extracted from blood of sheep infected experimentally with EV1. The pol assay detected in most cases lower numbers of viral molecules than gag assay, yielding some false negative results. The gag real-time RT PCR had a detection limit of 100 RNA molecules with a linearity over 5 orders of magnitude. This did not result in a lower performance of the RT PCR compared to the PCR in cells permissive for virus replication, which contain higher numbers of viral transcripts than proviral genomes. The real-time assays developed in this study, particularly the gag assay, provide a sensitive tool which can be used to quantify the viral load in experimental infections.

Lack of risk of transmission of caprine arthritis-encephalitis virus (CAEV) after an appropriate embryo transfer procedure

The aim of this study was to demonstrate that embryo transfer can be used to produce CAEV-free kids from CAEV-infected biological mothers when appropriate procedure is implemented. Twenty-eight goats that had tested positive for CAEV using PCR on vaginal secretions were used as embryo donors. Embryos with intact-ZP were selected and washed 10 times; they were then frozen and used for transfer into CAEV-free recipient goats. Nineteen of the 49 recipient goats gave birth, producing a total of 23 kids. Three blood samples were taken from each recipient goat, 10 days before, during, and 10 days after parturition; these were tested for CAEV antibodies using ELISA and for CAEV proviral DNA using PCR. The mothers were then euthanized. Tissue samples were taken from the lungs, udder, and retromammary and prescapular lymph nodes. The kids were separated from their mothers at birth. Seven of them died. At 4 months of age, 16 kids were subjected to drug-induced immunosuppression. Blood samples were taken every month from birth to 4 months of age; samples were then taken on days 15, 21, and 28 after the start of the immunosuppressive treatment. The kids were then euthanized and tissue samples taken from the carpal synovial membrane, lung tissue, prescapular lymph nodes, inguinal and retromammary lymph nodes, and uterus. All samples from the 19 recipient goats and 23 kids were found to be negative for CAEV antibodies and/or CAEV proviral DNA. Under acute conditions for infection this study clearly demonstrates that embryo transfer can be safely used to produce CAEV-free neonates from infected CAEV donors.

Potential risk of equine herpes virus 1 (EHV-1) transmission by equine embryo transfer

The objective of this study was to determine whether the 10 wash cycles proposed by the International Embryo Transfer Society (IETS) for bovine embryos efficiently decontaminated equine embryos exposed to equine herpes virus 1 (EHV-1) in vitro. Donor mares and stallions were individually screened and shown to be negative for the virus by PCR detection of EHV-1 DNA in blood leukocytes, semen, and uterine lavages in which embryos were recovered. Twenty embryos were recovered and randomly assigned to one of two groups: 10 embryos were exposed for 24h to infectious EHV-1 at 10(6)TCID(50)/ml, and 10 embryos were used as negative controls. Exposed embryos were washed in accordance with IETS recommendations for ruminant and porcine embryos, before being incubated for 24 h with semiconfluent rabbit kidney (RK13) cells to detect any cytopathic effects (CPE), and finally tested for the presence of EHV-1 viral DNA by PCR. The embryo washing media were also assayed for the virus on RK 13 cells and by PCR. Control embryos were neither exposed to the virus nor washed. EHV-1 was not found in the control embryos, or in the last five washes of the exposed embryos. However, the virus was detected in 7/10 of the embryos exposed to EHV-1 for 24h, as well as in the first five washes of the embryos. The gradual disappearance of EHV-1 from the 10 successive wash solutions from the exposed embryos and the detection of viral DNA in 7/10 washed embryos by PCR, demonstrated that the washing procedure was unable to remove EHV-1 and suggested that EHV-1 could be attached to the acellular layer surrounding embryos (zona pellucida or capsule) or had penetrated the embryo.

Activation/proliferation and apoptosis of bystander goat lymphocytes induced by a macrophage-tropic chimeric caprine arthritis encephalitis virus expressing SIV Nef

Caprine arthritis encephalitis virus (CAEV) is the natural lentivirus of goats, well known for its tropism for macrophages and its inability to cause infection in lymphocytes. The viral genome lacks nef, tat, vpu and vpx coding sequences. To test the hypothesis that when nef is expressed by the viral genome, the virus became toxic for lymphocytes during replication in macrophages, we inserted the SIVsmm PBj14 nef coding sequences into the genome of CAEV thereby generating CAEV-nef. This recombinant virus is not infectious for lymphocytes but is fully replication competent in goat macrophages in which it constitutively expresses the SIV Nef. We found that goat lymphocytes cocultured with CAEV-nef-infected macrophages became activated, showing increased expression of the interleukin-2 receptor (IL-2R). Activation correlated with increased proliferation of the cells. Interestingly, a dual effect in terms of apoptosis regulation was observed in exposed goat lymphocytes. Nef was found first to induce a protection of lymphocytes from apoptosis during the first few days following exposure to infected macrophages, but later it induced increased apoptosis in the activated lymphocytes. This new recombinant virus provides a model to study the functions of Nef in the context of infection of macrophages, but in absence of infection of T lymphocytes and brings new insights into the biological effects of Nef on lymphocytes.

In vitro cross-species infections using a caprine arthritis encephalitis lentivirus carrying the GFP marker gene

A caprine arthritis encephalitis virus (CAEV), carrying the green fluorescent protein (GFP) into the tat region was recently reported [Mselli-Lakhal, L., Guiguen, F., Greenland, T., Mornex, J.F., Chebloune, Y., 2006. Gene transfer system derived from the caprine arthritis-encephalitis lentivirus. J. Virol. Meth. 136, 177-184]. This construct, called pK2EGFPH replicated to titres up to 10(5)IU/ml on infection of caprine cells, and could be concentrated to 10(6)IU/ml by ultracentrifugation. In the present study, the pK2EGFPH construct was characterized better and used in cross-species infection studies. The pK2EGFPH virus could transduce GFP protein expression both to goat synovial membrane cells and to an immortalized goat milk epithelial cell line. The pK2EGFPH infected cells were demonstrated to express both GFP protein and CAEV viral proteins, as demonstrated by radioimmunoprecipitation and multinucleated cell formation. However GFP expression could not be maintained over passages. This vector was used to investigate cross-species infectious potential of CAEV. The bovine cell lines MDBK and GBK were found to be sensitive to infection while the human cell lines Hela, A431 and THP-1 were not. The pK2EGFPH vector should prove useful in studies of CAEV tropism both in vitro and in vivo.

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.

Detection of ovine lentivirus in the cumulus cells, but not in the oocytes or follicular fluid, of naturally infected sheep

The aim of this study was to examine the Maedi-Visna virus (MVV) infection status of oocytes, cumulus cells, and follicular fluid taken from 140 ewes from breeding flocks. MVV proviral-DNA and MVV RNA were detected using nested-PCR and RT-PCR MVV gene amplification, respectively in the gag gene. Nested-PCR analysis for MVV proviral-DNA was positive in peripheral blood mononuclear cells in 37.1% (52/140) of ewes and in 44.6% (125/280) of ovarian cortex samples. The examination of samples taken from ovarian follicles demonstrated that 8/280 batches of cumulus cells contained MVV proviral-DNA, whereas none of the 280 batches of oocytes taken from the same ovaries and whose cumulus cells has been removed, was found to be PCR positive. This was confirmed by RT-PCR analysis showing no MVV-viral RNA detection in all batches of oocytes without cumulus cells (0/280) and follicular fluid samples taken from the last 88 ovaries (0/88). The purity of the oocyte fraction and the efficacy of cumulus cell removal from oocytes was proved by absence of granulosa cell-specific mRNA in all batches of oocytes lacking the cumulus cells, using RT-PCR. This is the first demonstration that ewe cumulus cells harbor MVV genome and despite being in contact with these infected-cumulus cells, the oocytes and follicular fluid remain free from infection. In addition, the enzymatic and mechanical procedures we used to remove infected-cumulus cells surrounding the oocytes, are effective to generate MVV free-oocytes from MVV-infected ewes.

Cultured early goat embryos and cells are susceptible to infection with caprine encephalitis virus

Zona-pellucida-free embryos at 8-16 cell stage were co-cultured for 6 days in an insert over a mixed cell monolayer infected with CAEV-pBSCA. Embryos were washed and transferred to an insert on CAEV indicator goat synovial membrane cells for 6 h, then they were washed and cultivated in B2 Ménézo for 24 h, finally, embryo cells were dissociated and cultivated on a feeder monolayer for 8 days. After 5 weeks, multinucleated giant cells typical of CAEV infection were observed in indicator GSM cell monolayers. In the acellular medium, the early embryonic cells produced at least 10(3.25) TCID50/ml over 24 h. The monolayer of cultivated embryonic cells developed cytopathic lesions within 8 days, and CAEV RNA, CAEV proviral DNA and protein p28 of the capsid were detected. All of these results clearly demonstrate that caprine early embryonic cells are susceptible to infection with CAEV and that infection with this virus is productive.

Gene transfer system derived from the caprine arthritis-encephalitis lentivirus

Lentiviruses are attractive candidates for therapeutic vectors, because of their ability to infect non-dividing target cells. Vectors based on HIV-1 efficiently transfer gene expression to a variety of dividing or quiescent cells, but are subject to reservations on safety grounds. Caprine arthritis encephalitis virus (CAEV) is a lentivirus inducing only minor pathology in its natural host and in related species after cross-species transmission. To test the CAEV potential as vector for gene transfer, a cassette expressing the green fluorescent protein (GFP) under control of a CMV promoter was inserted into the CAEV genome, producing the pK2EGFPH vector. When pseudotyped with vesicular stomatitis virus (VSV)-G envelope protein, this vector allowed efficient transfer of GFP expression in human cells (up to 86% of GFP-expressing cells into the TE671 cell line). Three vectors carrying different parts of the viral gag, pol and env genes were then developed, together with a CAEV packaging system. These vectors allowed delimitation of the minimal CAEV sequences necessary for an improvement of vector production compared to the previously described CAEV-based vectors [Mselli-Lakhal et al., 1998. Defect in RNA transport and packaging are responsible for low transduction efficiency of CAEV-based vectors. Arc. Virol. 143, 681-695]. While our previous vectors were produced in a helper/vector system, the present vectors are produced in a helper/free system. However, these vector titers remain lower than those obtained with other lentiviral vectors carrying equivalent packaging sequences. We discuss on possible reasons of such differences and possible improvements.

Phylogenetic analysis of the gag region encoding the matrix protein of small ruminant lentiviruses: Comparative analysis and molecular epidemiological applications

Little sequence information exists on the matrix-protein (MA) encoding region of small ruminant lentiviruses (SRLV). Fifty-two novel sequences were established and permitted a first phylogenetic analysis of this region of the SRLV genome. The variability of the MA encoding region is higher compared to the gag region encoding the capsid protein and surprisingly close to that reported for the env gene. In contrast to primate lentiviruses, the deduced amino acid sequences of the N- and C-terminal domains of MA are variable. This permitted to pinpoint a basic domain in the N-terminal domain that is conserved in all lentiviruses and likely to play an important functional role. Additionally, a seven amino acid insertion was detected in all MVV strains, which may be used to differentiate CAEV and MVV isolates. A molecular epidemiology analysis based on these sequences indicates that the Italian lentivirus strains are closely related to each other and to the CAEV-CO strain, a prototypic strain isolated three decades ago in the US. This suggests a common origin of the SRLV circulating in the monitored flocks, possibly related to the introduction of infected goats in a negative population. Finally, this study shows that the MA region is suitable for phylogenetic studies and may be applied to monitor SRLV eradication programs.

Immunohistochemical detection of the p27 capsid protein of caprine arthritis-encephalitis virus (CAEV) in bone-marrow cells of seropositive goats

Bone-marrow samples were collected from 48 CAEV-seropositive, symptomless goats (30 kids, 18 adults). The samples were formalin-fixed and processed for histological examination. In addition, all samples were examined immunohistochemically with a monoclonal antibody (1A7) against the p27 capsid protein of maedi-visna virus, an antibody which cross-reacts with the Ca-p27 of CAEV. Samples from 16 goats (10/30 kids, 6/18 adults) showed positive immunolabelling of bone-marrow stromal cells (fibrocytes, endothelial cells and adipocytes) and of scattered macrophages, whereas haematopoietic cells were negative. The detection of viral Ca-p27 protein in bone-marrow fibrocytes was consistent with previous in-vitro studies which indicated that such cells are semi-permissive for CAEV infection. It is speculated that bone-marrow stromal cells represent a viral reservoir in symptomless animals.

Proviral DNA of caprine arthritis encephalitis virus (CAEV) is detected in cumulus oophorus cells but not in oocytes from naturally infected goats

The aim of this study was to determine whether oocytes taken from ovarian follicles in 123 naturally infected goats were carrying the proviral CAEV genome. Examination of DNA isolated from 190 batches of oocytes with intact cumulus cells and 190 batches of oocytes whose cumulus cells had been removed, taken from follicles of the same ovaries, demonstrated that 42/190 batches of oocytes with intact cumulus cells had the proviral CAEV genome, whereas none of the 190 batches of oocytes without cumulus cells were positive for the provirus. To confirm that the proviral genome was present in the cumulus cells and not in the oocyte cells, 586 oocytes from 56 different ovaries, were separated from their cumulus cells. The DNA was then extracted from each fraction and examined. The purity of the oocyte fraction was verified by searching for granulosa cell-specific mRNA, using RT-PCR; this was negative in all the batches of oocytes in which the cumulus cells had been removed. PCR analysis demonstrated that none of the oocytes without cumulus cells were positive, whereas 22/56 of the batches with cumulus cells were found to be positive. This study clearly demonstrates that despite being surrounded by infected cumulus cells, the oocytes are not infected, and that the enzymatic and mechanical technique for removing the cells surrounding the oocyte, as used in this study, is effective, thus enabling CAEV-free oocytes to be obtained from infected goats.

Genomic characterization of a slow/low maedi visna virus

The complete genomic sequence of a sheep lentivirus isolate that presents a slow/low phenotype in vitro has been determined. The virus, designated P1OLV, was isolated from lung cells of a naturally infected sheep in Portugal. Three overlapping DNA fragments amplified by PCR, and encompassing the entire viral genome were cloned and sequenced. This isolate has an overall similarity of approximately 80% with the K1514 Maedi Visna virus (MVV) and approximately 70% with the caprine arthritis encephalitis virus (CAEV) Co strain. Phylogenetic analysis based on SU and RT nucleotide sequences grouped P1OLV with previously reported ovine MVV. To determine the virus replication rate, sheep choroid plexus (SCP) and lung cells, macrophages (MØ), and goat synovial membrane (GSM) cells were inoculated with either P1OLV or with the lytic North American strain WLC-1. Viral RNA in culture supernatants was measured by one-tube real time quantitative RT-PCR. Significant differences were observed between the replication rates of the two viruses, with WLC-1 growing rapidly and to high levels in all the cells tested, while P1OLV replicated more slowly and to lower levels inducing persistent infections in lung and SCP cells. The U3 region of the LTR of P1OLV lacks the sequence repeats that are present in the LTRs of WLC-1 and MVV prototype K1514 and that contain additional binding sites for the AML(vis) transcriptional factor. To evaluate the contribution of LTR in the virus replication rate in vitro, we measured the basal activity of the promoter from P1OLV and WLC-1 in a luciferase-driven gene expression assay and lower levels of expression were achieved for P1OLV. The genetic and biological properties of P1OLV will be useful for the study of virus transcriptional factors and genes that may be responsible for the slow/low phenotype.

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.

Specific G2 arrest of caprine cells infected with a caprine arthritis encephalitis virus expressing vpr and vpx genes from simian immunodeficiency virus

Primate lentivirus (HIV and SIV) vpr accessory genes encode 12- to 14-kDa proteins which induce cell cycle arrest at the G2 phase of infected cells, preventing them from going through mitosis. Members of the HIV-2/SIVmac/SIVsmm group also encode a second closely related accessory protein called Vpx. Vpx and HIV Vpr are critical for virus replication in nondividing cells due to their participation in nuclear import of the preintegration complex. Caprine arthritis encephalitis virus (CAEV) and maedi visna virus are the natural lentiviruses of domestic goat and sheep, respectively, and their genomes do not carry vpr and vpx genes. In this study, we generated chimeric CAEV-based genomes carrying vpr and vpx genes from SIVmac239 and tested their ability to induce G2 cell cycle arrest in infected caprine cells. CAEV-pBSCAvpxvpr is the chimeric genome that was shown to be infectious and replication competent. Our data demonstrated that CAEV-pBSCAvpxvpr-infected goat synovial membrane cell monolayer developed more cytopathic effects and a high proportion of cells remained in the G2 phase of cell cycle. This G2 arrest was observed both at the early and at the late stages of infection, while minimal effect was observed with the parental CAEV-pBSCA. These results, described for the first time in mammalian cells other than those of primates, indicate that Vpr-induced G2 cell cycle arrest is not restricted to only primate cells. Thus, conservation of Vpx/Vpr protein functions in caprine cells suggests a possible role for these proteins in the virus life cycle and its ability to adapt to new hosts. The data presented here thus raise a pertinent question about the biological significance of the conservation of Vpr and Vpx functions in caprine cells despite the high phylogenic distance between primates and small ruminants.

Epithelial cells from goat oviduct are highly permissive for productive infection with caprine arthritis-encephalitis virus (CAEV)

Caprine oviduct epithelial cells (COEC) are commonly used in in vitro goat embryo production protocols to stimulate early embryonic development. These feeder cells are usually collected from slaughterhouses from unknown serological status animals for caprine arthritis-encephalitis virus (CAEV) infection which is frequent in many regions of the world. Tissues derived from this source may be contaminated with CAEV and the use of such material in in vitro fertilisation systems may contribute to transmission of this pathogen to the cultured embryos and dissemination via embryo transfer (ET). The aim of this study was to determine the permissiveness of COEC to CAEV replication in vitro. Cells were isolated from goats from certified CAEV-free herds and then were inoculated with two CAEV strains: the molecularly-cloned isolate of CAEV (CAEV-pBSCA) and the French field isolate (CAEV-3112). Cytopathic effects (CPE) were observed on cell culture monolayers inoculated with both CAEV strains. Expression of CAEV proteins was shown both by immunocytochemistry using anti-p24 gag specific antibodies and by immunoprecipitation using a hyperimmune serum. The CAEV proteins were correctly and properly processed by artificially-infected COEC and the titers of virus released into the supernatant reached 10(6) TCID(50)/ml 6 days post-inoculation. Although the macrophage lineage cells are the main centre of infection in the virus-positive animal, these findings suggest that epithelial cells may be important in the viral life cycle probably as a reservoir allowing the viral persistence, dissemination and pathogenesis. These results suggest also that the use in in vitro fertilisation systems of co-culture feeder cells that support efficient replication of CAEV to high titers could represent a serious risk for permanent transmission of virus to the cultured embryos and to the surrogate dam involved.

Efficient replication of caprine arthritis-encephalitis virus in goat granulosa cells

Recent reports demonstrated the susceptibility of epithelial cells from different organs to caprine arthritis-encephalitis virus (CAEV) both in vitro and in vivo. Since granulosa cells (GC) are of epithelial origin and currently used for in vitro oocyte maturation, we addressed the question whether these cells are susceptible or resistant to CAEV infection. GC were isolated from goats from certified CAEV-free herds. PCR analysis on GC DNA using CAEV specific primers confirmed the absence of CAEV infection and immunocytochemistry using specific K813 anti-cytokeratin monoclonal antibodies confirmed the epithelial nature of GC. These cells were then inoculated with CAEV using two strains: the CAEV-pBSCA molecular clone and the CAEV-3112 French field isolate. Cytopathic effects (CPE) were observed on cell culture monolayers inoculated with both CAEV strains. Expression of CAEV proteins was shown both by immunocytochemistry using anti-p24 gag specific antibodies and by immunoprecipitation using an hyperimmune serum. Supernatant of infected cells were shown to contain high titers (ranging 10(5) tissue culture infectious doses 50 per ml: TCID(50) per ml) of infectious cytopathic viruses when assayed onto the indicator goat synovial membrane (GSM) cells. Our findings demonstrate the large cell tropism of CAEV and suggest that GC could serve as a reservoir for the virus during the sub-clinical phase of infection. Furthermore, given the high seroprevalence of CAEV in the all industrialised countries and the large number of ovaries derived from unknown serological status animals used for in vitro goat embryo production, one can conclude that these feeder cell cultures might be a potential source of early transmission of CAEV to goat embryos.

Host range of small-ruminant lentivirus cytopathic variants determined with a selectable caprine arthritis- encephalitis virus pseudotype system

The small-ruminant lentiviruses ovine maedi-visna virus (MVV) and caprine arthritis-encephalitis virus (CAEV) cause encephalitis, progressive pneumonia, arthritis, and mastitis in sheep and goats. Icelandic MVV strains, which are lytic in tissue culture, have a wide species distribution of functional receptors, which includes human cells. In contrast, functional receptors for the nonlytic CAEV CO are absent from human cells. To determine if the wide species distribution of functional receptors is a common property of MVV strains or related to cytopathic phenotype, we tested the infectivity of viruses pseudotyped with the envelope glycoproteins of MVV K1514, CAEV CO, and lytic and nonlytic North American MVV strains to cells of different species. Replication-defective CAEV proviral constructs lacking the env, tat, and vif genes and carrying the neomycin phosphotransferase gene in the vif-tat region were developed for the infectivity assays. Cotransfection of human 293T cells with these proviral constructs and plasmids expressing CAEV, MVV, or vesicular stomatitis virus envelope glycoproteins produced infectious pseudotyped virus which induced resistance of infected cells to G418. Using these pseudotypes, we confirmed the wide species distribution of Icelandic MVV receptors and the narrow host range of CAEV. However, functional receptors for the two North American MVV strains tested, unlike the Icelandic MVV and similar to CAEV, were limited to cells of ruminant species, regardless of cytopathic phenotype. The results indicate a differential receptor recognition by MVV strains which is unrelated to cytopathic phenotype.

Lack of functional receptors is the only barrier that prevents caprine arthritis-encephalitis virus from infecting human cells

Barriers to replication of viruses in potential host cells may occur at several levels. Lack of suitable and functional receptors on the host cell surface, thereby precluding entry of the virus, is a frequent reason for noninfectivity, as long as no alternative way of entry (e.g., pinocytosis, antibody-dependent adsorption) can be exploited by the virus. Other barriers can intervene at later stages of the virus life cycle, with restrictions on transcription of the viral genome, incorrect translation and posttranslational processing of viral proteins, inefficient viral assembly, and release or efficient early induction of apoptosis in the infected cell. The data we present here demonstrate that replication of caprine arthritis-encephalitis virus (CAEV) is restricted in a variety of human cell lines and primary tissue cultures. This barrier was efficiently overcome by transfection of a novel infectious complete-proviral CAEV construct into the same cells. The successful infection of human cells with a vesicular stomatitis virus (VSV) G-pseudotyped Env-defective CAEV confirmed that viral entry is the major obstacle to CAEV infection of human cells. The fully efficient productive infection obtained with the VSV-G-protein-pseudotyped infectious CAEV strengthened the evidence that lack of viral entry is the only practical barrier to CAEV replication in human cells. The virus thus produced retained its original host cell specificity and acquired no propensity to propagate further in human cultures.

Experimental infection of Mouflon-domestic sheep hybrids with caprine arthritis-encephalitis virus

OBJECTIVE

To determine whether monocyte-derived macrophages from Mouflon-domestic sheep hybrids (Ovis musimon X Ovis spp) were susceptible to productive infection with caprine arthritis-encephalitis virus (CAEV) in vitro and whether experimental inoculation of Mouflon-domestic sheep hybrids with a molecularly cloned CAEV would result in persistent infection.

ANIMALS

5 Mouflon hybrids.

PROCEDURE

Macrophage monolayers were inoculated with virus in vitro. Three animals were inoculated with virus intratracheally.

RESULTS

Productive replication of CAEV was demonstrated in monocyte-derived macrophages following in vitro and in vivo inoculation. Titer of infectious cytopathic CAEV produced by macrophages from the Mouflon hybrids was similar to titers produced by macrophages from an infected goat or by synovial membrane cells. Isolation of virus from monocyte-derived macrophages and use of a semiquantitative polymerase chain reaction assay to amplify a portion of the viral genome demonstrated persistent virus replication in all 3 inoculated animals. Two weeks after inoculation of sheep, approximately 1 of 5,000 monocytes was harboring the virus.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicate that Mouflon-domestic sheep hybrids are susceptible to infection with isolates of CAEV that cause infection in domestic small ruminants.

Goat milk epithelial cells are highly permissive to CAEV infection in vitro

The main route of small ruminant lentivirus dissemination is the ingestion of infected cells present in colostrum and milk from infected animals. However, whether only macrophages or other cell subtypes are involved in this transmission is unknown. We derived epithelial cell cultures, 100% cytokeratin positive, from milk of naturally infected and noninfected goats. One such culture, derived from a naturally infected goat, constitutively produced a high titer of virus in the absence of any cytopathic effect. The other cultures, negative for natural lentivirus infection, were tested for their susceptibility to infection with the CAEV-CO strain and a French field isolate CAEV-3112. We showed that milk epithelial cells are easily infected by either virus and produce viruses at titers as high as those obtained in permissive goat synovial membrane cells. The CAEV-CO strain replicated in milk epithelial cells in absence of any cytopathic effect, whereas the CAEV-3112 field isolate induced both cell fusion and cell lysis. Our results suggest that CAEV-infected milk epithelial cells of small ruminants may play an important role in virus transmission and pathogenesis.

North American and French caprine arthritis-encephalitis viruses emerge from ovine maedi-visna viruses

The full extent of genetic diversity among small ruminant lentiviruses (SRLVs), i.e., caprine arthritis encephalitis viruses (CAEVs) and maedi-visna viruses (MVVs), remains unknown. This is due in part to the fact that few sequences of CAEV are available. To contribute to this knowledge, gag, pol, and env nucleotide sequences from an SRLV named CA680 originating from a goat from western France were determined. This analysis revealed that this virus is closely related to the Cork and 63 CAEV American isolates. Mismatched amino acids between the CA680 virus and prototype CAEVs ranged from 6.7, 0. 7, and 17.5% for gag, pol, and SU sequences, respectively. The differences between the CA680 virus and MVV prototypes ranged from 16.5, 12.5, and 32.3% for the protein sequences, respectively. A screening using a heteroduplex mobility assay (HMA) adapted to SRLVs revealed that 6 of 10 caprine virus field isolates were closely related to CA680, indicating that this latter isolate was a prototype of CAEVs common in the west of France. Phylogenetic trees drawn using CA, RT, or SU sequences of numerous SRLVs and rooted with EIAV sequences revealed that CA680 and CAEV prototypes, all infectious for goat, clustered in one group. From these HMA and phylogenetic analyses, it appears that U.S. and French caprine SRLVs form a clade that had emerged from a much more diverse group containing all SRLVs infectious for sheep. These ovine SRLVs form a more ancient group in which the EIAV is rooted.