Modulation of the long terminal repeat promoter activity of small ruminant lentiviruses by steroids

The genetic variability of small-ruminant lentiviruses and its impact on tropism, the development of diagnostic tests and vaccines and the effectiveness of control programmes

Introduction

Maedi-visna virus and caprine arthritis encephalitis virus are two closely related lentiviruses which cause multisystemic, progressive and persistent infection in goats and sheep. Because these viruses frequently cross the species barrier, they are considered to be one genetic group called small-ruminant lentiviruses (SRLV). They have in vivo tropism mainly for monocytes and macrophages and organ tropism with unknown mechanisms. Typical clinical signs are pneumonia in sheep, arthritis in goats, and mastitis in both species. Infection with SRLV cannot currently be treated or prevented, and control programmes are the only approaches to avoiding its spread. These programmes rely mainly on annual serological testing and elimination of positive animals. However, the high genetic and antigenic variability of SRLV complicate their early and definitive diagnosis. The objective of this review is to summarise the current knowledge of SRLV genetic variation and its implications for tropism, the development of diagnostic tests and vaccines and the effectiveness of control and eradication programmes.

Material and Methods

Subject literature was selected from the PubMed and the Google Scholar databases.

Results

The high genetic diversity of SRLV affects the performance of diagnostic tools and therefore control programmes. For the early and definitive diagnosis of SRLV infection, a combination of serological and molecular tests is suggested. Testing by PCR can also be considered for sub-yearling animals. There are still significant gaps in our knowledge of the epidemiology, immunology and biology of SRLV and their impact on animal production and welfare.

Conclusion

This information may aid selection of the most effective SRLV spread reduction measures.

Alternative Molecular Tools for the Fight against Infectious Diseases of Small Ruminants: Native Sicilian Sheep Breeds and Maedi-Visna Genetic Susceptibility

Simple Summary

Local breeds represent a precious reservoir of genetic diversity, crucial to adapting to environmental and climate changes and reacting to evolving diseases. In Sicily, four native dairy breeds, namely Valle del Belìce, Comisana, Barbaresca, and Pinzirita, have adapted to low-input farming systems and semiarid environments, having an essential role in producing high-quality milk and typical dairy products. Maedi-visna (MV) is one of the most important chronic diseases affecting the sheep sector worldwide, causing production losses. Different target genes play an important role in immunity and in genetic resilience to MV, such as TMEM154, TLR9, MYD88, and CCR5. A major host genetic component to sheep MV susceptibility was identified in the ovine TMEM154 gene. Animals with either of TMEM154 haplotypes that encode glutamate at position 35 (E35) of the protein are at higher risk of MV infection than those homozygous with lysine at position 35 (K35). In the tested Sicilian breeds, animals carrying the allele E35 showed a greater risk of being serologically positive. Comisana, Barbaresca, and Pinzirita breeds showed a good frequency of the protective allele K35, whilst a high frequency of risk allele was found in the Valle del Belìce breed, related to the selection strategies addressed to obtain a productive dairy sheep. Our results highlight the importance of the preservation of autochthonous breeds as a reservoir of natural resistance against infectious disease.

Abstract

Maedi-visna (MV) is a disease caused by small ruminant lentiviruses. It is included in the list of notifiable terrestrial animal diseases due to economic losses and animal welfare harm in the sheep sector. To date, control programs remain the onliest approach to avoiding infection. The allelic variant p.Glu35Lys (E35K) of the TMEM154 gene has been strongly associated with host vulnerability to MV illness. The present study aimed to investigate the association of TMEM154 E35K allele frequencies with MV susceptibility in native Sicilian sheep breeds. More than 400 animals from 14 local sheep were serologically tested and genotyped for the TMEM154 E35K polymorphism. The local breeds displayed different values of MV seroprevalence, with the lowest antibody prevalence in Barbaresca and Pinzirita breeds. TMEM154 protective allele (K35) was less frequent than the risk allele (E35) in Valle del Belìce breed, whereas the other three breeds showed a more balanced alleles distribution. A positive association between seroprevalence and genotype was found in the entire sample set. The risk of infection resulted in more than 3-fold times as high in sheep with EK and EE genotype compared to the KK genotype. Our data could be helpful in establishing selection breeding programs aimed at reducing MV infection in Sicilian sheep farming and encouraging the breeding of native breeds.

Maedi-Visna virus: current perspectives

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