Infection of dendritic cells by the Maedi-Visna lentivirus

Isolation and Identification of Caprine Arthritis Encephalitis Virus from Animals in the Republic of Mordovia

This article presents the results of virological and genetic studies of an isolate of caprine arthritis encephalitis (CAE) virus from the republic of Mordovia, Russian Federation. The isolate was found during monitoring studies of goat blood samples for the viral genome, and the presence of antibodies to lentiviruses was detected. According to the recommendation of the OIE, the positive result of PCR was confirmed with nucleotide sequencing. It was found that the obtained nucleotide sequence is identical to the genome of small ruminant lentiviruses presented in the GenBank database. Phylogenetic analysis showed that the isolate "Mordovia-2018" was included in the same cluster with an isolate from the Tver region of the Russian Federation detected in 2008. The sequence of the fragment of the env-gene of the isolate from the republic of Mordovia is available in GenBank under the number MN186380.1. To isolate the virus, a fraction of peripheral blood monocyte cells from the animal's blood was added to a monolayer of lamb synovial membrane cell culture, and ten passages were carried out. The first manifestations of the cytopathic effect were observed after the third passage on the eighth day of cultivation in the form of single large cells of irregular shape with 5-7 nuclei. At the seventh passage, multiple syncytium with 7-12 nuclei were observed. At subsequent passage levels, the formation of syncytium containing more than 10-14 nuclei was observed.

[Indurative mastitis in a herd of Dorper sheep caused by an infection with Maedi Visna virus]

This case report describes indurative mastitis in a herd of sheep caused by Maedi Visna virus (MVV) infection. Reduced udder formation after delivery, small, indurated udders and increased losses of lambs were observed in a herd of Dorper sheep. Examination of the mammary gland and milk did not reveal findings characteristic of chronic bacterial mastitis. The protein supply was insufficient which may have contributed to reduced milk yield, but was considered unlikely as cause for the induration of the mammary gland. Nineteen of the 21 mothers were positive for MVV by serology. Mammary gland and supramammary lymph nodes were collected in a sheep with indurated udder at the time of slaughter. Meat inspection did not reveal lesions in any other organs. One part of the mammary gland showed a mild to moderate multifocal lymphohistiocytic mastitis, the other exhibited a severe diffuse lymphohistiocytic mastitis with atrophy of the glandular acini, vasculopathy, fibrosis and calcification. MVV antigen was visualized by immunohistochemistry in macrophages, dendritic cells, epithelial cells and endothelial cells in the mammary gland, and macrophages and dendritic cells in the supramammary lymph nodes. A large amount of MVV provirus was detected in the supramammary lymph nodes and the severely indurated part of the mammary gland by PCR. In conclusion, indurative mastitis as a result of a systemic infection may occur independently of the commonly known manifestations of Maedi Visna in the lung and central nervous system. MVV should be considered as differential diagnosis in mastitis of sheep. The MVV status of the herd can be tested by serological detection of specific antibodies. Additionally, characteristic histological lesions are present in the mammary gland. MVV antigen can also be detected by immunohistochemistry and MVV provirus by PCR in the altered mammary gland and regional lymph nodes.

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 Diversity of the LTR Region of Polish SRLVs and Its Impact on the Transcriptional Activity of Viral Promoters

A long terminal repeat (LTR) plays an indispensable role in small ruminant lentivirus (SRLV) gene expression. In this study, we present the LTR sequence of Polish SRLVs representing different subtypes, and analyzed their impact on SRLV promoter activity, as measured in transient transfection assays. Although certain nucleotide motifs (AML(vis), TATA box and the polyadenylation site (AATAAA)) were conserved across sequences, numerous mutations within the LTR sequences have been identified. Single nucleotide polymorphisms (SNPs) were detected in both regulatory (AP-1, AP-4, Stat and Gas) and non-regulatory sequences, and subtype-specific genetic diversity in the LTR region of Polish SRLVs was observed. In vitro assays demonstrated subtype-specific functional differences between the LTR regions of distinct SRLV subtypes. Our results revealed that the promoter activity of Polish strains was lower (1.64-10.8-fold) than that noted for the K1514 reference strain; however, the differences in most cases were not statistically significant. The lowest promoter activity was observed for strains representing subtype A5 (mean 69.067) while the highest promoter activity was observed for strain K1514 representing subtype A1 (mean 373.48). The mean LTR activities of strains representing subtypes A12, A17, A23, A18 and A24 were 91.22, 137.21, 178.41, 187.05 and 236.836, respectively. The results of the inter-subtype difference analysis showed that the promoter activity of strains belonging to subtype A5 was significantly lower than that for subtype A12 strains (1.32-fold; p < 0.00). The promoter activities of the A5 strain were 1.98-fold and 2.58-fold less active than that of the A17 and A23 strains, and the promoter activities of A12 strains were 1.955 and 1.5 times lower than the promoter activity of A23 and A17 strains, respectively. Furthermore, the promoter activity of A17 strains was 1.3 lower than the promoter activity of A23 strains. Our findings suggest that subtype-specific genetic diversity, mainly in the transcription factor's binding sites, has an impact on their transcriptional activity, producing a distinct activity pattern for the subtypes. This study provides new information that is important for better understanding the function of the SRLV LTR. However, further research including more strains and subtypes as well as other cell lines is needed to confirm these findings.

Phylogenetic Analysis of Small Ruminant Lentiviruses Originating from Naturally Infected Sheep and Goats from Poland Based on the Long Terminal Repeat Sequences

Introduction

Previous gag and env sequence studies placed Polish small ruminant lentiviruses (SRLVs) isolated from sheep and goats in subtypes B1, B2, A1, A5, A12, A13, A16-A18, A23, A24 and A27. This study extended the genetic/phylogenetic analysis of previously identified Polish SRLV strains by contributing long terminal repeat (LTR) sequences.

Material and Methods

A total of 112 samples were analysed. Phylogenetic analyses were carried out on the LTR fragment using the neighbour-joining, maximum likelihood, and unweighted pair group method with arithmetic mean methods.

Results

Polish caprine and ovine LTR sequences clustered within group A and grouped in at least 10 clusters (subtypes A1, A5, A12, A13, A16-A18, A23, A24 and A27). Most of the Polish strains (78%) belonged to the same subtype by the indication of the gag, env and LTR genomic regions. Discrepancies in affiliation depending on the particular sequence were observed in 24 (21%) strains, most of which came from mixed-species flocks where more than one SRLV genotype circulated. Sequences of the LTR reflected subtype-specific patterns. Several subtype-specific markers were identified, e.g. a unique substitution of T to A in the fifth position of the TATA box in A17, A27, A20 and B3.

Conclusion

This study provides valuable insights into the genetic diversity of SRLV field strains in Poland, their phylogenetic relationships and their position in the recently established SRLV classification. Our results confirmed the existence of the ten subtypes listed and the readier emergence of new SRLV variants in mixed-species flocks.

A high-density genome-wide association with absolute blood monocyte count in domestic sheep identifies novel loci

Monocytes are a core component of the immune system that arise from bone marrow and differentiate into cells responsible for phagocytosis and antigen presentation. Their derivatives are often responsible for the initiation of the adaptive immune response. Monocytes and macrophages are central in both controlling and propagating infectious diseases such as infection by Coxiella burnetii and small ruminant lentivirus in sheep. Genotypes from 513 Rambouillet, Polypay, and Columbia sheep (Ovis aries) were generated using the Ovine SNP50 BeadChip. Of these sheep, 222 animals were subsequently genotyped with the Ovine Infinium^® HD SNP BeadChip to increase SNP coverage. Data from the 222 HD genotyped sheep were combined with the data from an additional 258 unique sheep to form a 480-sheep reference panel; this panel was used to impute the low-density genotypes to the HD genotyping density. Then, a genome-wide association analysis was conducted to identify loci associated with absolute monocyte counts from blood. The analysis used a single-locus mixed linear model implementing EMMAX with age and ten principal components as fixed effects. Two genome-wide significant peaks (p < 5x10^-7) were identified on chromosomes 9 and 1, and ten genome-wide suggestive peaks (p < 1x10^-5) were identified on chromosomes 1, 2, 3, 4, 9, 10, 15, and 16. The identified loci were within or near genes including KCNK9, involved into cytokine production, LY6D, a member of a superfamily of genes, some of which subset monocyte lineages, and HMGN1, which encodes a chromatin regulator associated with myeloid cell differentiation. Further investigation of these loci is being conducted to understand their contributions to monocyte counts. Investigating the genetic basis of monocyte lineages and numbers may in turn provide information about pathogens of veterinary importance and elucidate fundamental immunology.

An outbreak of visna-maedi in a flock of sheep in Southern Brazil

Visna-maedi is a multisystemic and progressive inflammatory disease caused by a non-oncogenic retrovirus (Visna-maedi virus, VMV). An outbreak of visna-maedi occurred in Southern Brazil in sheep with clinical signs of blindness and stumbling gait. At post-mortem examination, all animals had similar lesions, including heavy non-collapsed lungs and multifocal yellow areas in the cerebral white matter, affecting mainly the periventricular region. These lesions corresponded histologically to lymphocytic interstitial pneumonia and histiocytic periventricular encephalitis surrounding areas of necrosis, in addition to significant demyelination in the brain. Serology was performed in all the sheep from the flock and 14% were seropositive for VMV. The presence of VMV was confirmed through PCR and partial sequencing of the 5'LTR. Sequencing demonstrated that the virus had 89.7 to 90.0% of nucleotide identity with VMV strains reported in the USA. This is the first description of clinical disease related to VMV in Brazil leading to economic losses. This study calls for the need to implement control measures to prevent the spread of small ruminant lentiviruses in Brazil.

Molecular Characterization of Small Ruminant Lentiviruses Isolated from Polish Goats with Arthritis

Previous studies revealed that the small ruminant lentivirus (SRLV) population in Poland is highly heterogeneous. All SRLVs detected from Polish sheep and goats so far have belonged to subtypes B1, B2, A1, A5, A12, A13, A16, A17, A18, A23 and A24. However, all characterized strains originated from asymptomatic animals. This is the first study that characterizes the molecular properties of SRLVs isolated from different organs of six arthritic goats. Segments from three genomic regions (gag, LTR and env) were analyzed. In addition, we quantified the SRLV proviral load in the blood and different organs and examined its association with different degrees of histopathological lesions. All sequences obtained from the goats involved in this study were homogeneous, showing an average degree of variability of 4.8%, 3.7% and 8.8% for gag, LTR and env, respectively. Phylogenetic analysis revealed that the sequences from the analyzed goats were clustered within SRLVs group A and formed a new subtype within this group, tentatively named A27. The histopathological examination of the lung, mammary gland, synovial membranes of joints and brain of the analyzed goats revealed evidence of inflammatory processes associated with SRLV infection, which was confirmed by positive immunohistochemistry assays. No significant correlation was observed between histological features and alterations in the sequences from different tissues. No tissue-specific signature pattern was identified. It was shown that animals with a higher proviral load showed more lesion severity in various SRLV-affected tissues, indicating a positive association between these two parameters. Our results also revealed differences in the SRLV load between animals even though the sequences derived from all of the goats were closely related, suggesting that host factors may restrict and control viral replication. This study provides new information about SRLV variants isolated from arthritic goats; however, more studies, including the isolation and characterization of biological properties of these viruses, should be performed to evaluate their pathogenic potential.

Molecular Characterization of Small Ruminant Lentiviruses in Polish Mixed Flocks Supports Evidence of Cross Species Transmission, Dual Infection, a Recombination Event, and Reveals the Existence of New Subtypes within Group A

Small ruminant lentiviruses (SRLVs) are a group of highly divergent viruses responsible for global infection in sheep and goats. In a previous study we showed that SRLV strains found in mixed flocks in Poland belonged to subtype A13 and A18, but this study was restricted only to the few flocks from Małopolska region. The present work aimed at extending earlier findings with the analysis of SRLVs in mixed flocks including larger numbers of animals and flocks from different part of Poland. On the basis of gag and env sequences, Polish SRLVs were assigned to the subtypes B2, A5, A12, and A17. Furthermore, the existence of a new subtypes, tentatively designed as A23 and A24, were described for the first time. Subtypes A5 and A17 were only found in goats, subtype A24 has been detected only in sheep while subtypes A12, A23, and B2 have been found in both sheep and goats. Co-infection with strains belonging to different subtypes was evidenced in three sheep and two goats originating from two flocks. Furthermore, three putative recombination events were identified within gag and env SRLVs sequences derived from three sheep. Amino acid (aa) sequences of immunodominant epitopes in CA protein were well conserved while Major Homology Region (MHR) had more alteration showing unique mutations in sequences of subtypes A5 and A17. In contrast, aa sequences of surface glycoprotein exhibited higher variability confirming type-specific variation in the SU5 epitope. The number of potential N-linked glycosylation sites (PNGS) ranged from 3 to 6 in respective sequences and were located in different positions. The analysis of LTR sequences revealed that sequences corresponding to the TATA box, AP-4, AML-vis, and polyadenylation signal (poly A) were quite conserved, while considerable alteration was observed in AP-1 sites. Interestingly, our results revealed that all sequences belonging to subtype A17 had unique substitution T to A in the fifth position of TATA box and did not have a 11 nt deletion in the R region which was noted in other sequences from Poland. These data revealed a complex picture of SRLVs population with ovine and caprine strains belonging to group A and B. We present strong and multiple evidence of dually infected sheep and goats in mixed flocks and present evidence that these viruses can recombine in vivo.

Molecular Characterization of Small Ruminant Lentiviruses of Subtype A5 Detected in Naturally Infected but Clinically Healthy Goats of Carpathian Breed

Small ruminant lentiviruses (SRLVs) are widespread in sheep and goats in Poland, and several subtypes were identified and molecularly characterized up to date. This is the first study that characterizes the molecular properties of A5 strains of SRLV detected in naturally infected, but clinically healthy, Carpathian goats. Segments from three genomic regions (gag, env, and LTR) were analyzed. Genetic distance, pairwise comparison, and phylogenetic analysis revealed that Polish SRLV A5 sequences are closely related to the Swiss and German A5 sequences suggesting a common origin. The epidemiological linkage was identified particularly between the small ruminants of Germany and Poland. Amino acid sequences of immunodominant regions in CA protein were well-conserved within analyzed strains; however, they showed some remarkable changes like substitution (D) to (E), at position 90 in Major Homology Region (MHR) and (T) to (S), at position 141 in epitope 3. In contrast, aa sequences of surface glycoprotein exhibited the highest variability confirming type-specific variation in SU5 epitope. Two deletions in the U3 region of A5 strains were noted: One (8 nt) located near the 5′ end of the U3 region and the other (29 nt) located in the central region of U3. Additionally, all A5 strains had specific deletion (10 nt) in the R region. Furthermore, we did not find a correlation between copies of the CAAAT motif and clinical manifestation in infected animals. These data showed some remarkable features in the viral genome of A5 strains, which may be related to the attenuated phenotype in vivo, characterized by the lack of any clinical signs in infected goats. Certainly, more studies are required to support the hypothesis that these A5 viruses are of low pathogenicity for goats. We want to focus our future studies on the analysis of the whole genomes of these isolates and their biological properties, as well as on clinicopathological studies of goats infected by A5 SRLV, aiming to clarify the pathogenic potential of these viruses.

Characterization of minimal lesions related to the presence of visna/maedi virus in the mammary gland and milk of dairy sheep

Background

In order to characterize the complete range of lesions, especially minimal, affecting mammary gland and viral antigen distribution and target cells using immunohistochemistry in naturally Visna/maedi (VM) 84 infected sheep were studied, forty-four from flocks with clinical cases (A) and 35 randomly sampled from two abattoirs (B) together with five negative controls (C). An immunocytochemistry technique was developed and further milk samples (n = 39) were used to study viral excretion, carrier cells and the role of milk and colostrum in the transmission of the disease.

Results

All sheep from group C and three sheep from group B were negative to VM in tissue sections by histopathology, immunohistochemistry and PCR, and also in serum using ELISA. Several degrees of CD3 + lymphocytic interstitial mastitis were observed in groups A and B: minimal (+) n = 26 sheep; moderate (++), n = 32 and severe (+++), n = 12. No differences in lesion distribution were observed between groups A and B. Viral presence was confirmed by immunohistochemistry using two different antibodies and/or PCR in every tissue with lesions while serology was negative in six sheep with lesions. Two milk samples taken from milk tanks from two flocks from group A and fourteen milk samples from 29 infected sheep from group B were positive to VM (most of them from animals with moderate and severe lesions). Positivity was only found in macrophages, even in focal and minimal lesions, while no positivity was observed in epithelial or any other cells in either tissue and milk samples.

Conclusions

This new observation of the minimal lesions described in this work increased the prevalence of VM lesions in mammary gland up to 90.9% and VM should be considered as a differential diagnosis when minimal interstitial lesions are detected. A high prevalence of VM was observed in intensive milk-producing sheep, ELISA serology did not detect as positivity all infected animals, while histology, IHC or PCR showed higher sensitivity. The cytological technique developed was very useful in milk-cell studies using hematoxylin and eosin and immunocytochemistry. Viral detection in milk samples (16/39) confirms a potential but limited role of milk/colostrum in viral transmission.

Electronic supplementary material

The online version of this article (10.1186/s12917-019-1855-3) contains supplementary material, which is available to authorized users.

Compartmentalization of Subtype A17 of Small Ruminant Lentiviruses between Blood and Colostrum in Infected Goats Is Not Exclusively Associated to the env Gene

The compartmentalization of small ruminant lentiviruses (SRLVs) subtype A17 was analyzed in colostrum and peripheral blood leukocyte cells of three naturally infected goats. This study aimed to analyze heterogeneity of the SRLV env (V4V5) gene, which encodes neutralizing epitopes of SU glycoprotein, the gag gene encoding capsid protein (CA), and LTR, a noncoding region, responsible for determination of cell tropism. Compartmentalization was assessed using six established tree or distance-based methods, including permutation test to determine statistical significance. We found statistical evidence of compartmentalization between blood and colostrum in all infected goats although phylogenetic evidence of such compartmentalization was not obvious. Our study demonstrated that compartmentalization is not exclusively specific to the env gene, as we revealed that gag and LTR sequences are also compartmentalized between blood and colostrum. The work also confirms the combined use of different methods as essential for reliable determination of intrahost viral compartmentalization. Identifying and characterizing distinct viral subpopulations and the genetic evolution of SRLV in specific anatomical sites enhances our overall understanding of SRLV pathogenesis, immune control, and particularly virus transmission.

Duplex nested-PCR for detection of small ruminant lentiviruses

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

Prospects in Innate Immune Responses as Potential Control Strategies against Non-Primate Lentiviruses

Lentiviruses are infectious agents of a number of animal species, including sheep, goats, horses, monkeys, cows, and cats, in addition to humans. As in the human case, the host immune response fails to control the establishment of chronic persistent infection that finally leads to a specific disease development. Despite intensive research on the development of lentivirus vaccines, it is still not clear which immune responses can protect against infection. Viral mutations resulting in escape from T-cell or antibody-mediated responses are the basis of the immune failure to control the infection. The innate immune response provides the first line of defense against viral infections in an antigen-independent manner. Antiviral innate responses are conducted by dendritic cells, macrophages, and natural killer cells, often targeted by lentiviruses, and intrinsic antiviral mechanisms exerted by all cells. Intrinsic responses depend on the recognition of the viral pathogen-associated molecular patterns (PAMPs) by pathogen recognition receptors (PRRs), and the signaling cascades leading to an antiviral state by inducing the expression of antiviral proteins, including restriction factors. This review describes the latest advances on innate immunity related to the infection by animal lentiviruses, centered on small ruminant lentiviruses (SRLV), equine infectious anemia virus (EIAV), and feline (FIV) and bovine immunodeficiency viruses (BIV), specifically focusing on the antiviral role of the major restriction factors described thus far.

Genetic Characterization and Phylogenetic Analysis of Small Ruminant Lentiviruses Detected in Spanish Assaf Sheep with Different Mammary Lesions

Small Ruminant Lentiviruses (SRLVs) are widespread in many countries and cause economically relevant, slow, and persistent diseases in sheep and goats. Monitoring the genetic diversity of SRLVs is useful to improve the diagnostic tools used in the eradication programs. In this study, SRLVs detected in Spanish Assaf sheep with different grades of lymphoproliferative mastitis were sequenced. Genetic characterization showed that most samples belonged to type A and were closer to Spanish SRLV isolates previously classified as A2/A3. Four samples belonged to subtype B2 and showed higher homology with Italian B2 strains than with Spanish B2 isolates. Amino acid sequences of immuno-dominant epitopes in the gag region were very conserved while more alterations were found in the LTR sequences. No significant correlations were found between grades of mastitis and alterations in the sequences although samples with similar histological features were phylogenetically closer to each other. Broader genetic characterization surveys in samples with different grades of SRLV-lesions are required for evaluating potential correlations between SRLV sequences and the severity of diseases.

Inflammatory Lesion Patterns in Target Organs of Visna/Maedi in Sheep and their Significance in the Pathogenesis and Diagnosis of the Infection

Ovine visna/maedi (VM) infection is characterized by the development of chronic inflammatory lesions in different organs, mainly in the lung, mammary gland and central nervous system (CNS), with either histiocytic or lymphocytic pattern predominance being described in the CNS. To help to understand the role of host immune response in the development of these patterns, 50 naturally-infected sheep and eight non-infected sheep from intensive milk-producing flocks were studied. The histological lesion patterns in the three main target organs in each sheep were characterized. Lesion severity was determined, including minimal lesions. A histiocytic pattern was observed in 23 sheep (46%), a lymphocytic inflammatory pattern in 19 sheep (38%) and a mixed inflammatory pattern in eight sheep (16%). Forty animals showed moderate or severe lesions (80%), while 10 had minimal lesions (20%). Moderate or severe lesions affected only one target organ in 20 sheep (50%), two organs in 14 sheep (35%) and all three target organs in six sheep (15%). Infection was confirmed by immunohistochemistry (IHC) using an antibody specific for p28 of VM virus/caprine arthritis and encephalitis virus and by polymerase chain reaction (PCR) in all sheep. Minimal inflammatory lesions associated with positive IHC and PCR were observed. The results suggest that the development of a predominant inflammatory pattern in different organs within the same animal may be related to the host immune response. Minimal and focal lesions, not considered previously, should be taken into account when formulating a differential diagnosis in affected sheep.

Maedi-visna virus persistence: Antigenic variation and latency

Maedi-visna virus (MVV), a lentivirus of sheep, shares with other lentiviruses the ability to establish a lifelong infection. In this study five sheep were infected intravenously with MVV and housed together with a number of uninfected sheep for natural transmission. All virus isolates from ten sheep that had been infected naturally had multiple mutations in the principal neutralization domain in Env and were antigenic variants, while three of four isolates from the carrier sheep had identical sequences to the infecting strain and were not antigenic variants. There was evidence of positive selection in the gene, particularly in amino acids comprising the neutralization epitope and some adjacent glycosylation sites. Together these results suggest that virus persistence is acquired by a reservoir of latent viruses, and that there is selection for antigenic variants of virus that is transmitted naturally.

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.

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.

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.

Comparative Analysis of Tat-Dependent and Tat-Deficient Natural Lentiviruses

The emergence of human immunodeficiency virus (HIV) causing acquired immunodeficiency syndrome (AIDS) in infected humans has resulted in a global pandemic that has killed millions. HIV-1 and HIV-2 belong to the lentivirus genus of the Retroviridae family. This genus also includes viruses that infect other vertebrate animals, among them caprine arthritis-encephalitis virus (CAEV) and Maedi-Visna virus (MVV), the prototypes of a heterogeneous group of viruses known as small ruminant lentiviruses (SRLVs), affecting both goat and sheep worldwide. Despite their long host-SRLV natural history, SRLVs were never found to be responsible for immunodeficiency in contrast to primate lentiviruses. SRLVs only replicate productively in monocytes/macrophages in infected animals but not in CD4+ T cells. The focus of this review is to examine and compare the biological and pathological properties of SRLVs as prototypic Tat-independent lentiviruses with HIV-1 as prototypic Tat-dependent lentiviruses. Results from this analysis will help to improve the understanding of why and how these two prototypic lentiviruses evolved in opposite directions in term of virulence and pathogenicity. Results may also help develop new strategies based on the attenuation of SRLVs to control the highly pathogenic HIV-1 in humans.

Genetic subgroup of small ruminant lentiviruses that infects sheep homozygous for TMEM154 frameshift deletion mutation A4Δ53

Small ruminant lentivirus (SRLV) infections of sheep are influenced by genetics on both the host and pathogen sides. Genetic variation in the ovine transmembrane 154 (TMEM154) gene associates with infection susceptibility, and distinct SRLV genetic subgroups infect sheep in association with their TMEM154 diplotypes. In this study, a novel SRLV subgroup was identified that naturally infected sheep with various TMEM154 diplotypes, including those homozygous for a rare frameshift mutation (A4 delta53), which is predicted to abolish TMEM154 protein function. Thus, these SRLVs may infect sheep that lack functional TMEM154, and may not be restricted by TMEM154 diplotypes in establishing infections.

Plasticity of migrating CD1b+ and CD1b- lymph dendritic cells in the promotion of Th1, Th2 and Th17 in response to Salmonella and helminth secretions

Dendritic cells (DCs) are pivotal in the development of specific T-cell responses to control pathogens, as they govern both the initiation and the polarization of adaptive immunity. To investigate the capacities of migrating DCs to respond to pathogens, we used physiologically generated lymph DCs (L-DCs). The flexible polarization of L-DCs was analysed in response to Salmonella or helminth secretions known to induce different T cell responses. Mature conventional CD1b⁺ L-DCs showed a predisposition to promote pro-inflammatory (IL-6), pro-Th1 (IL-12p40) and anti-inflammatory (IL-10) responses which were amplified by Salmonella, and limited to only IL-6 induction by helminth secretions. The other major population of L-DCs did not express the CD1b molecule and displayed phenotypic features of immaturity compared to CD1b⁺ L-DCs. Salmonella infection reduced the constitutive expression of TNF-α and IL-4 mRNA in CD1b^- L-DCs, whereas this expression was not affected by helminth secretions. The cytokine response of T cells promoted by L-DCs was analysed in T cell subsets after co-culture with Salmonella or helminth secretion-driven CD1b⁺ or CD1b^- L-DCs. T cells preferentially expressed the IL-17 gene, and to a lesser extent the IFN-γ and IL-10 genes, in response to Salmonella-driven CD1b⁺ L-DCs, whereas a preferential IL-10, IFN-γ and IL-17 gene expression was observed in response to Salmonella-driven CD1b^- L-DCs. In contrast, a predominant IL-4 and IL-13 gene expression by CD4⁺ and CD8⁺ T cells was observed after stimulation of CD1b⁺ and CD1b^- L-DCs with helminth secretions. These results show that mature conventional CD1b⁺ L-DCs maintain a flexible capacity to respond differently to pathogens, that the predisposition of CD1b^- L-DCs to promote a Th2 response can be oriented towards other Th responses, and finally that the modulation of migrating L-DCs responses is controlled more by the pathogen encountered than the L-DC subsets.

Small ruminant macrophage polarization may play a pivotal role on lentiviral infection

Small ruminant lentiviruses (SRLV) infect the monocyte/macrophage lineage inducing a long-lasting infection affecting body condition, production and welfare of sheep and goats all over the world. Macrophages play a pivotal role on the host’s innate and adaptative immune responses against parasites by becoming differentially activated. Macrophage heterogeneity can tentatively be classified into classically differentiated macrophages (M1) through stimulation with IFN-γ displaying an inflammatory profile, or can be alternatively differentiated by stimulation with IL-4/IL-13 into M2 macrophages with homeostatic functions. Since infection by SRLV can modulate macrophage functions we explored here whether ovine and caprine macrophages can be segregated into M1 and M2 populations and whether this differential polarization represents differential susceptibility to SRLV infection. We found that like in human and mouse systems, ovine and caprine macrophages can be differentiated with particular stimuli into M1/M2 subpopulations displaying specific markers. In addition, small ruminant macrophages are plastic since M1 differentiated macrophages can express M2 markers when the stimulus changes from IFN-γ to IL-4. SRLV replication was restricted in M1 macrophages and increased in M2 differentiated macrophages respectively according to viral production. Identification of the infection pathways in macrophage populations may provide new targets for eliciting appropriate immune responses against SRLV infection.

Retroviral infections in sheep and goats: small ruminant lentiviruses and host interaction

Small ruminant lentiviruses (SRLV) are members of the Retrovirus family comprising the closely related Visna/Maedi Virus (VMV) and the Caprine Arthritis-Encephalitis Virus (CAEV), which infect sheep and goats. Both infect cells of the monocyte/macrophage lineage and cause lifelong infections. Infection by VMV and CAEV can lead to Visna/Maedi (VM) and Caprine Arthritis-Encephalitis (CAE) respectively, slow progressive inflammatory diseases primarily affecting the lungs, nervous system, joints and mammary glands. VM and CAE are distributed worldwide and develop over a period of months or years, always leading to the death of the host, with the consequent economic and welfare implications. Currently, the control of VM and CAE relies on the control of transmission and culling of infected animals. However, there is evidence that host genetics play an important role in determining Susceptibility/Resistance to SRLV infection and disease progression, but little work has been performed in small ruminants. More research is necessary to understand the host-SRLV interaction.

A polytropic caprine arthritis encephalitis virus promoter isolated from multiple tissues from a sheep with multisystemic lentivirus-associated inflammatory disease

Caprine arthritis encephalitis virus (CAEV) is a lentivirus that infects both goats and sheep and is closely related to maedi-visna virus that infects sheep; collectively, these viruses are known as small ruminant lentiviruses (SRLV). Infection of goats and sheep with SRLV typically results in discrete inflammatory diseases which include arthritis, mastitis, pneumonia or encephalomyelitis. SRLV-infected animals concurrently demonstrating lentivirus-associated lesions in tissues of lung, mammary gland, joint synovium and the central nervous system are either very rare or have not been reported. Here we describe a novel CAEV promoter isolated from a sheep with multisystemic lentivirus-associated inflammatory disease including interstitial pneumonia, mastitis, polyarthritis and leukomyelitis. A single, novel SRLV promoter was cloned and sequenced from five different anatomical locations (brain stem, spinal cord, lung, mammary gland and carpal joint synovium), all of which demonstrated lesions characteristic of lentivirus associated inflammation. This SRLV promoter isolate was found to be closely related to CAEV promoters isolated from goats in northern California and other parts of the world. The promoter was denoted CAEV-ovine-MS (multisystemic disease); the stability of the transcription factor binding sites within the U3 promoter sequence are discussed.

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.

Genetic characterization of small ruminant lentiviruses circulating in naturally infected sheep and goats in Ontario, Canada

Maedi-visna virus (MVV) and caprine arthritis encephalitis virus (CAEV) are related members of a group of small ruminant lentiviruses (SRLVs) that infect sheep and goats. SRLVs are endemic in many countries, including Canada. However, very little is known about the genetic characteristics of Canadian SRLVs, particularly in the province of Ontario. Given the importance of surveillance and eradication programs for the control of SRLVs, it is imperative that the diagnostic tests used to identify infected animals are sensitive to local strains of SRLVs. The aim of this work was to characterize SRLV strains circulating in Ontario and to evaluate the variability of the immunodominant regions of the Gag protein. In this study, the nearly complete gag sequence of 164 SRLVs, from 130 naturally infected sheep and 32 naturally infected goats from Ontario, was sequenced. Animals belonged to distantly located single and mixed species (sheep and goats) farms. Ovine lentiviruses from the same farm tended to cluster more closely together than did caprine lentiviruses from the same farm. Sequence analysis revealed a higher degree of heterogeneity among the caprine lentivirus sequences with an average inter-farm pairwise DNA distance of 10% and only 5% in the ovine lentivirus group. Interestingly, amplification of SRLVs from ELISA positive sheep was successful in 81% of cases, whereas amplification of SRLV proviral DNA was only possible in 55% of the ELISA positive goat samples; suggesting that a significant portion of caprine lentiviruses circulating in Ontario possess heterogeneity at the primer binding sites used in this study. Sequences of sheep and goat SRLVs from Ontario were assembled into phylogenetic trees with other known SRLVs and were found to belong to sequence groups A2 and B1, respectively, as defined by Shah et al. (2004a). A novel caprine lentivirus with a pairwise genetic difference of 15.6-25.4% relative to other group B subtypes was identified. Thus we suggest the designation of a novel subtype, B4, within the caprine lentivirus-like cluster. Lastly, we demonstrate evidence of recombination between ovine lentiviruses. These results emphasize the broad genetic diversity of SRLV strains circulating in the province of Ontario and show that the gag region is suitable for phylogenetic studies and may be applied to monitor SRLV eradication programs.

Visna/Maedi virus genetic characterization and serological diagnosis of infection in sheep from a neurological outbreak

An extensive outbreak characterized by the appearance of neurological symptoms in small ruminant lentivirus (SRLV) infected sheep has been identified in Spain, but the genetic characteristics of the strain involved and differential diagnostic tools for this outbreak remain unexplored. In this work, 23 Visna-affected naturally infected animals from the outbreak, 11 arthritic animals (both groups presenting anti-Visna/Maedi virus serum antibodies), and 100 seronegative animals were used. Eight of the Visna-affected animals were further studied post-mortem by immunohistochemistry. All had lesions in spinal cord, being the most affected part of the central nervous system in six of them. A representative strain of the outbreak was isolated. Together with other proviral sequences from the outbreak the virus was assigned to genotype A2/A3. In vitro culture of the isolate revealed that viral production was slow/low in fibroblast-like cells but it was high in blood monocyte-derived macrophages. The long terminal repeat (LTR) of the viral genome of this isolate lacked an U3-duplication, but its promoter activity in fibroblast-like cells was normal compared to other strains. Thus, viral production could not be inferred from the LTR promoter activity in this isolate. Analysis of the viral immunodominant epitopes among SRLV sequences of the outbreak and other known sequences allowed the design of a synthetic SU peptide ELISA that detected the Visna affected animals, representing a tool of epidemiological interest to control viral spread of this highly pathogenic strain.

Important mammalian veterinary viral immunodiseases and their control

This paper offers an overview of important veterinary viral diseases of mammals stemming from aberrant immune response. Diseases reviewed comprise those due to lentiviruses of equine infectious anaemia, visna/maedi and caprine arthritis encephalitis and feline immunodeficiency. Diseases caused by viruses of feline infectious peritonitis, feline leukaemia, canine distemper and aquatic counterparts, Aleutian disease and malignant catarrhal fever. We also consider prospects of immunoprophylaxis for the diseases and briefly other control measures. It should be realised that the outlook for effective vaccines for many of the diseases is remote. This paper describes the current status of vaccine research and the difficulties encountered during their development.

Capacities of migrating CD1b+ lymph dendritic cells to present Salmonella antigens to naive T cells

Dendritic cells (DCs) are well known as professional antigen-presenting cells (APC) able to initiate specific T-cell responses to pathogens in lymph nodes (LN) draining the site of infection. However, the respective contribution of migratory and LN-resident DCs in this process remains unclear. As DC subsets represent important targets for vaccination strategies, more precise knowledge of DC subsets able to present vaccine antigens to T cells efficiently is required. To investigate the capacities of DCs migrating in the lymph (L-DCs) to initiate a specific T-cell response, we used physiologically generated DCs collected from a pseudoafferent lymphatic cannulation model in sheep. The CD1b⁺ L-DCs were assessed for presenting antigens from the vaccine attenuated strain of Salmonella enterica serovar Abortusovis. CD1b⁺ L-DCs were able to phagocytose, process and to present efficiently Salmonella antigens to effector/memory T cells in vitro. They were shown to be efficient APC for the priming of allogeneic naive T cells associated with inducing both IFN-γ and IL-4 responses. They were also efficient in presenting Salmonella antigens to autologous naive T cells associated with inducing both IFN-γ and IL-10 responses. The capacities of L-DCs to process and present Salmonella antigens to T cells were investigated in vivo after conjunctival inoculation of Salmonella. The CD1b⁺ L-DCs collected after inoculation were able to induce the proliferative response of CD4⁺ T cells suggesting the in vivo capture of Salmonella antigens by the CD1b⁺ L-DCs, and their potential to present them directly to CD4⁺ T cells. In this study, CD1b⁺ L-DCs present potential characteristics of APC to initiate by themselves T cell priming in the LN. They could be used as target cells for driving immune activation in vaccinal strategies.

Small ruminant lentiviruses: immunopathogenesis of visna-maedi and caprine arthritis and encephalitis virus

The small ruminant lentiviruses include the prototype for the genus, visna-maedi virus (VMV) as well as caprine arthritis encephalitis virus (CAEV). Infection of sheep or goats with these viruses causes slow, progressive, inflammatory pathology in many tissues, but the most common clinical signs result from pathology in the lung, mammary gland, central nervous system and joints. This review examines replication, immunity to and pathogenesis of these viruses and highlights major differences from and similarities to some of the other lentiviruses.

Diagnostic assays used to control small ruminant lentiviruses

The serologic diagnostic tests, such as the agar gel immunodiffusion assay and various types of enzyme-linked immunosorbent assays (ELISAs), have contributed to the reduction of small ruminant lentivirus (SRLV) infections worldwide. Because there are no treatments or efficacious vaccines, the serologic diagnostic tests have supported most of the eradication efforts by testing and removal or separation of adult animals that generate antibodies to SRLVs. With the advent of molecular diagnostics, standard and quantitative polymerase chain reaction (PCR)-based assays for the detection of provirus in peripheral blood cells are becoming more common and aid in the detection of infected goats and sheep before antibody detection by ELISA in some animals. Performance of the serologic and molecular diagnostic tests is dependent upon a number of factors, including the format of the assay, the percentage of identity between the viral nucleotide sequences in a flock or herd of a certain geographic region and the sequences used to generate SRLV test reagents, and the intrinsic pathogenesis or amount of provirus and SRLV antibody generated in a species or individual small ruminant. In addition, small ruminant genomics may help with establishing genetic markers of SRLV infection and disease, which could also aid eradication or reduction of SRLVs from herds and flocks throughout the world.

Characterization of ovine TLR7 and TLR8 protein coding regions, detection of mutations and Maedi Visna virus infection

Toll-like receptors (TLRs) 2, 3, 4, 7, 8 and 9 play a crucial role in the recognition of viral entities and modulation of the innate immune system. This work presents sequence analysis of ovine TLR7 and TLR8 genes, depicts novel mutations and describes frequencies of mutations in Maedi Visna infected and healthy sheep. Totally 48 samples of the breed Tsigai were analyzed for the presence of mutations. Within 20 mutations, 14 were silent whereas 6 were missense. The frequencies of missense mutations in the Maedi Visna infected compared to non-infected sheep were: Lys115Glu (P-0.766, F-test), Asn117 (P-0.380) and Lys818Arg (P-0.739). These three mutations were localized in extra LRR (lucine rich repeat) region of TLR7, while mutation Ile73Leu (P-0.498) was located within LRR2 motif. Both mutations in TLR8, Asn165Lys (P-1.0) and Tyr349His (P-0.700), were present in extra LRR region. The secondary structure analysis of ovine TLR7 and TLR8 revealed conserved LRR motif structure, however with some irregularities compared to cattle and human. Transmembrane domains of TLR7 and TLR8 showed 100% homology between sheep and cattle wherein no mutations were found. In both TLRs TIR domains were highly conserved with occurrence of 4 silent mutations. Mutations in TLR7 and TLR8 may play an important role as predisposition factor for Maedi Visna infection. Considering the sequence homology among sheep, cattle and human genes encoding TLR7 and TLR8, we predict their similar function, localization and downstream signaling.

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.

Mapping and characterization of visna/maedi virus cytotoxic T-lymphocyte epitopes

CD8(+) cytotoxic T-lymphocyte (CTL) responses have been shown to be important in the control of human and simian immunodeficiency virus infections. Infection of sheep with visna/maedi virus (VISNA), a related lentivirus, induces specific CD8(+) CTL in vivo, but the specific viral proteins recognized are not known. To determine which VISNA antigens were recognized by sheep CTL, we used recombinant vaccinia viruses expressing the different genes of VISNA: in six sheep (Finnish LandracexDorset crosses, Friesland and Lleyn breeds) all VISNA proteins were recognized except TAT. Two sheep, shown to share major histocompatibility complex (MHC) class I alleles, recognized POL and were used to map the epitope. The pol gene is 3267 bp long encoding 1088 aa. By using recombinant vaccinia viruses a central portion (nt 1609-2176, aa 537-725) was found to contain the CTL epitope and this was mapped with synthetic peptides to a 25 aa region (aa 612-636). When smaller peptides were used, a cluster of epitopes was detected: at least three epitopes were present, at positions 612-623: DSRYAFEFMIRN; 620-631: MIRNWDEEVIKN; and 625-635: EEVIKNPIQAR. A DNA-prime-modified vaccinia virus Ankara (MVA)-boost strategy was employed to immunize four sheep shown to share MHC class I allele(s) with the sheep above. Specific CTL activity developed in all the immunized sheep within 3 weeks of the final MVA boost although half the sheep showed evidence of specific reactivity after the DNA-prime immunizations. This is the first report, to our knowledge, of induction of CTL by a DNA-prime-boost method in VISNA infection.

Small-ruminant lentivirus enhances PrPSc accumulation in cultured sheep microglial cells

Sheep scrapie is the prototypical transmissible spongiform encephalopathy (prion disease), which has a fundamental pathogenesis involving conversion of normal cellular prion protein (PrP(C) [C superscript stands for cellular]) to disease-associated prion protein (PrP(Sc) [Sc superscript stands for sheep scrapie]). Sheep microglial cell cultures, derived from a prnp 136VV/171QQ near-term fetal brain, were developed to study sheep scrapie in the natural host and to investigate potential cofactors in the prion conversion process. Two culture systems, a primary cell culture and a cell line transformed with the large T antigen of simian virus 40, were developed, and both were identified as microglial in origin as indicated by expression of several microglial phenotype markers. Following exposure to PrP(Sc), sheep microglial cells demonstrated relatively low levels (transformed cell line) to high levels (primary cell line) of PrP(Sc) accumulation over time. The accumulated PrP(Sc) demonstrated protease resistance, an inferred beta-sheet conformation (as determined by a commercial enzyme-linked immunosorbent assay), specific inhibition by anti-PrP antibodies, and was transmissible in a dose-dependent manner. Primary microglia coinfected with a small-ruminant lentivirus (caprine arthritis encephalitis virus-Cork strain) and PrP(Sc) demonstrated an approximately twofold increase in PrP(Sc) accumulation compared to that of primary microglia infected with PrP(Sc) alone. The results demonstrate the in vitro utility of PrP(Sc)-permissive sheep microglial cells in investigating the biology of natural prion diseases and show that small-ruminant lentiviruses enhance prion conversion in cultured sheep microglia.

Mucosal immunization against ovine lentivirus using PEI-DNA complexes and modified vaccinia Ankara encoding the gag and/or env genes

Sheep were immunized against Visna/Maedi virus (VMV) gag and/or env genes via the nasopharynx-associated lymphoid tissue (NALT) and lung using polyethylenimine (PEI)-DNA complexes and modified vaccinia Ankara, and challenged with live virus via the lung. env immunization enhanced humoral responses prior to but not after VMV challenge. Systemic T cell proliferative and cytotoxic responses were generally low, with the responses following single gag gene immunization being significantly depressed after challenge. A transient reduction in provirus load in the blood early after challenge was observed following env immunization, whilst the gag gene either alone or in combination with env resulted in significantly elevated provirus loads in lung. However, despite this, a significant reduction in lesion score was observed in animals immunized with the single gag gene at post-mortem. Inclusion of IFN-gamma in the immunization mixture in general had no significant effects. The results thus showed that protective effects against VMV-induced lesions can be induced following respiratory immunization with the single gag gene, though this was accompanied by an increased pulmonary provirus load.

Experimental infection of sheep with visna/maedi virus via the conjunctival space

Experiments were performed to determine whether visna/maedi virus (VMV), a small ruminant lentivirus (SRLV), could infect sheep via ocular tissues. The EV1 strain of VMV was administered into the conjunctival space of uninfected sheep, and the animals monitored for the presence of provirus DNA and anti-VMV antibodies in blood. The results showed that provirus DNA appeared in peripheral blood mononuclear cells of all animals within a few weeks of receiving either 10(6) TCID50 or 10(3) TCID50 of VMV. Of the animals receiving the higher dose of virus via the conjunctival space, two seroconverted by 7 and 10 weeks post-infection, one seroconverted 8 months post-infection, and one had not seroconverted by 15 months post-infection. With the lower virus dose, the animals infected via the trachea seroconverted by 4 and 14 weeks, respectively. After ocular infection with this dose, one animal showed a transitory seroconversion with low levels of antibody, peaking at 2 weeks post-administration. The remaining three of the animals infected via the eyes did not seroconvert over a period of 13 months. At post-mortem, evidence for the presence of proviral DNA was obtained from ocular tissue, lungs or mediastinal lymph node in both groups of animals. Histological analysis of lung tissue from animals receiving the lower dose of virus showed the presence of early inflammatory lesions. The results thus show for the first time that transmission of VMV can occur via ocular tissues, suggesting that the conjunctival space may be an additional route of natural transmission.