Evaluation of vaccines for ovine lentivirus infection

First molecular characterization of visna/maedi viruses from naturally infected sheep in Turkey

Recent worldwide serological and genetic studies of small ruminant lentiviruses (SRLV) have led to the description of new genotypes and the development of new diagnostic tests. This study investigated the detection and molecular characterization of visna/maedi virus (VMV) infection in serum and blood samples from pure and mixed sheep breeds acquired from different regions in Turkey using ELISA and PCR techniques. The prevalence of VMV was 67.8 % by ELISA and/or LTR-PCR with both assays showing a medium level of agreement (kappa: 0.26; ± 0.038 CI). Positivity of VMV in sheep increased according to the age of the animal, although PCR positivity was higher than ELISA in young individuals. Phylogenetic analysis of 33 LTR sequences identified two distinct clades that were closely related to American and Greek LTR sequences. Phylogenetic analysis of 10 partial gag gene sequences identified A2, A3, A5, A9, A11 subtypes of genotype A SRLVs. In vitro culture of all isolates in fetal sheep lung cells (FSLC) showed a slow/low phenotype causing less or no lytic infection compared with infection with the WLC-1 American strain characterized by a rapid/highly lytic phenotype. Phylogenetic analysis revealed that Turkish VMV sequences preceded the establishment of American or Greek strains that were associated with the migration of sheep from the Middle East to Western Europe several centuries ago. This is the first study that describes Turkish VMV sequences with the molecular characterization of LTR and gag genes, and it strongly suggests that SRLV-genotype A originated in Turkey.

Characterization of ovine Toll-like receptor 9 protein coding region, comparative analysis, detection of mutations and maedi visna infection

One of the major roles of innate immunity system is the recognition and the determination of the nature of the antigen. This ability is encompassed by specific receptors as Toll-like receptors (TLRs). TLR9 recognizes bacterial and viral CpG motifs, while their potent immunostimulation effect seems to be promising for lentiviral therapies. Recent studies, however, show the presence of a big polymorphism within the TLR genes and the linkage between substitutions and susceptibility to various infections. Moreover, different recognition ability seems to be utilized by different species and possibly breeds. In this study, we characterized the protein coding region of ovine TLR9 gene. By using comparative analysis of two closely related species and humans, we suggest, which characteristics of protein could be responsible for altered recognition. Furthermore, analyzing the presence of the substitutions, we show the intraspecies polymorphism and its possible implications, while attempting to define the association of discovered substitutions with the maedi visna infection.

Extensive rearing hinders Maedi-Visna Virus (MVV) infection in sheep

Maedi-Visna Virus (MVV) seroprevalence and its relationship with housing and mode of rearing of replacement ewe-lambs was investigated in 38 non-randomly selected sheep-flocks in Spain. They included extensive lamb-producing Manchega cross-bred flocks raised almost permanently at pasture, semi-intensive Latxa dairy flocks housed 2-8 months/year and intensively raised Assaf dairy flocks housed most time and at higher stocking density in less ventilated buildings than other flocks. Most flocks raised replacement lambs naturally with their dams until weaning and as a separate flock thereafter until lambing at one year of age. Seroprevalence (95% confidence intervals) was 77%, 25% and 5% (4-6) in intensive, semi-intensive and extensive flocks, respectively and the median (interquartile range) flock-seroprevalence was 82% (66-94) in intensive flocks, 31% (14-31) in semi-intensive flocks and 4% (0-7) in extensive flocks. Seroprevalence was lowest in one year-old sheep and increased to flock levels during the year after introduction into the adult flock in most intensive flocks and more gradually in other flocks. Adult flock seroprevalence was associated with housing time but this relationship was not evident within a particular rearing system, indicating that other unknown factors are critical in horizontal MVV-transmission. Low seroprevalence in extensive flocks further supports previous indications that lactogenic MVV-infection is relatively inefficient and horizontal transmission is necessary to ensure long-term maintenance of MVV and this could explain that MVV has not been reported from countries with mainly extensively reared sheep such as Australia and New Zealand. Moreover, it indicates that MVV-control in extensive and semi-intensive flocks can be simple and inexpensive.

Maedi-Visna and ovine progressive pneumonia

Maedi-Visna and ovine progressive pneumonia are disease of sheep that are caused by ovine lentivirus and characterized by chronic inflammation of the lungs, mammary glands, joints, and central nervous system. Although tremendous progress in research has led to a better understanding of the pathogenesis of these diseases, many questions still remain. Much of the mystery is the result of the complexity of the ovine lentivirus genome and the intricate interactions of the virus with the host during replication. Discoveries in molecular virology are shedding light on these interactions and novel approaches to prevent and control lentivirus infections are being explored. There is hope that some of these approaches will eventually be used to eradicate these diseases.