Use of small ruminant lentivirus-infected rams for artificial insemination

Small Ruminant Lentivirus Infection in Sheep and Goats in North Portugal: Seroprevalence and Risk Factors

Small ruminant lentiviruses (SRLVs) are transmitted among ovine and caprine species. This disease is a severe problem for small ruminant production, not only for animals' well-being but also for flocks' efficiency. The main aim of this research was to quantify the seroprevalence and associated risk factors for SRLV infection in the northern region of Portugal. Samples were collected from a total of 150 flocks, of which 129 (86.0%; 95% CI: 80.67%-91.33%) had at least one seropositive animal. Out of 2607 individual blood samples, 1074 (41.2%) were positive for SRLVs. Risk factors associated with SRLV infection were species (caprine), age (>2 years old), flock size (>100 animals), production system (intensive), food production system (milk), type of activity (professional), participation in livestock competitions (yes), replacement young ewe bought (yes), and natural feeding management (yes). This knowledge empowers the implementation of effective preventive measures. Overall, biosecurity measures should be promoted and implemented with the main aim of reducing viral transmission and reducing the prevalence of this disease. We recognise that government authorities should promote and audit voluntary control and eradication programs in small ruminant flocks in the region studied.

Infectious pathogens potentially transmitted by semen of the black variety of the Manchega sheep breed: Health constraints for conservation purposes

Conservation of genetic resources from endangered breeds may be conducted through germinal banks. Preservation of healthy samples is paramount to avoid preserving pathogens shed with germinal products. The black variety of Manchega sheep (BMS), and endangered breed endemic to south-central Spain, is the subject of a conservation program; a germinal bank has been recently established. However, several pathogens circulating in BMS flocks may be shed with semen and threaten BMS preservation. Therefore, we investigated the sanitary status of BMS flocks and semen samples from 4 of the 17 flocks in which this variety is bred worldwide. A serological screening for Maedi-Visna virus, bluetongue virus, Pestivirus spp., Brucella spp., Coxiella burnetii, Chlamydophila spp., Mycobacterium tuberculosis complex, Mycobacterium avium paratuberculosis, Anaplasma spp., Mycoplasma agalactiae, Toxoplasma gondii and Neospora caninum was performed to assess for pathogens potentially shed by semen. Semen samples from 11 of the 35 BMS rams and 4 samples from coexisting rams of the white variety (WMS) were analyzed by PCR to detect Maedi-Visna virus, C. burnetii, Anaplasma marginale, Anaplasma phagocytophilum and T. gondii. Maedi-Visna virus RNA was detected in 3 semen samples (2 BMS and 1 WMS) while C. burnetii DNA was detected in 3 samples from WMS rams. Pathogens that can be transmitted by semen were present in BMS flocks, and Maedi-Visna virus and C. burnetii showed the highest potential for transmission by artificial insemination. Our results point to the need of testing semen samples kept for conservation purposes of BMS before using them for artificial insemination.

Small ruminant lentiviruses (SRLVs) break the species barrier to acquire new host range

Zoonotic events of simian immunodeficiency virus (SIV) from non-human primates to humans have generated the acquired immunodeficiency syndrome (AIDS), one of the most devastating infectious disease of the last century with more than 30 million people dead and about 40.3 million people currently infected worldwide. Human immunodeficiency virus (HIV-1 and HIV-2), the two major viruses that cause AIDS in humans are retroviruses of the lentivirus genus. The genus includes arthritis-encephalitis virus (CAEV) and Maedi-Visna virus (MVV), and a heterogeneous group of viruses known as small ruminant lentiviruses (SRLVs), affecting goat and sheep. Lentivirus genome integrates into the host DNA, causing persistent infection associated with a remarkable diversity during viral replication. Direct evidence of mixed infections with these two closely related SRLVs was found in both sheep and goats. The evidence of a genetic continuum with caprine and ovine field isolates demonstrates the absence of an efficient species barrier preventing cross-species transmission. In dual-infected animals, persistent infections with both CAEV and MVV have been described, and viral chimeras have been detected. This not only complicates animal trade between countries but favors the risk that highly pathogenic variants may emerge as has already been observed in the past in Iceland and, more recently, in outbreaks with virulent strains in Spain. SRLVs affecting wildlife have already been identified, demonstrating the existence of emergent viruses adapted to new hosts. Viruses adapted to wildlife ruminants may acquire novel biopathological properties which may endanger not only the new host species but also domestic ruminants and humans. SRLVs infecting sheep and goats follow a genomic evolution similar to that observed in HIV or in other lentiviruses. Lentivirus genetic diversity and host factors leading to the establishment of naturally occurring virulent versus avirulent infections, in addition to the emergence of new strains, challenge every aspect of SRLV control measures for providing efficient tools to prevent the transmission of diseases between wild ungulates and livestock.

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.