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

Abstract

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.

Genetic Characterization of Small Ruminant Lentiviruses Isolated from Dairy Sheep in Greece

“…Considering that immunodominant linear epitopes of capsid protein are strongly associated with the type-specific host immune response [ 46 , 53 , 55 ], their role in serological diagnosis is crucial. The investigation of genetic heterogeneity in these epitopes among the different SRLV strains could reveal diagnostic drawbacks of the existent serological diagnostic tools and contribute to the development of highly efficient ones [ 56 , 57 ]. Also, serotyping diagnostic tools discriminating the different SRLV genotypes have been developed using subunits of the viral capsid protein [ 58 , 59 ].…”

A Combined Approach for the Characterization of Small Ruminant Lentivirus Strains Circulating in the Islands and Mainland of Greece

“…Control programs mainly rely on testing and removing positive animals. However, the genetic variability of SRLVs and the lack of gold-standard diagnostic tests able to identify all the possible genotypes and subtypes represent a challenge and limitation in these programs [15].…”

“…SRLVs are characterized by a high genetic and antigenic variability, having one of the fastest-evolving genomes thanks to the lack of proofreading ability of their reverse transcriptase [4]. This high heterogeneity strongly influences both the in vivo and in vitro properties of SRLVs, as well as their diagnostic test results [1,[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19].…”

“…Agar gel immunodiffusion (AGID) and enzyme-linked immunosorbent assay (ELISA) are the most commonly used and prescribed by the WOAH [14]. Of these, ELISA tests are widely used, since their good performance is combined with scalability and cost-effectiveness, while AGID is usually applied to confirm ELISA results [15,16]. However, indirect diagnosis can be affected by the variability of circulating strains, delayed seroconversion, and variations in antibody responses [1,17].…”

Detection of small ruminant Lentivirus proviral DNA in red deer from Poland

“…The most likely routes of SRLVs transmission are ingestion of SRLV-contaminated milk or colostrum or via inhalation of respiratory secretions through close contact between animals. However, transmission through contaminated feeding and drinking equipment, contaminated water and feces is also possible [ 4 , 8 – 10 ].…”