Abstract
Small ruminant lentiviruses include members that infect sheep (ovine lentivirus [OvLV]; also known as ovine progressive pneumonia virus/maedi-visna virus) and goats (caprine arthritis encephalitis virus [CAEV]). Breed differences in seroprevalence and proviral concentration of OvLV had suggested a strong genetic component in susceptibility to infection by OvLV in sheep. A genetic marker test for susceptibility to OvLV has been developed recently based on the TMEM154 gene with validation data from over 2,800 sheep representing nine cohorts. While no single genotype has been shown to have complete resistance to OvLV, consistent association in thousands of sheep from multiple breeds and management conditions highlight a new strategy for intervention by selective breeding. This genetic marker-assisted selection (MAS) has the potential to be a useful addition to existing viral control measures. Further, the discovery of multiple additional genomic regions associated with susceptibility to or control of OvLV suggests that additional genetic marker tests may be developed to extend the reach of MAS in the future. This review will cover the strengths and limitations of existing data from host genetics as an intervention and outline additional questions for future genetic research in sheep, goats, small ruminant lentiviruses, and their host-pathogen interactions.
Highlights
It has been shown that these viruses of sheep and goats may be better described more broadly as small ruminant lentiviruses (SRLVs) [2], in part because each virus infects both host species [5,6]
The large effect size and high minor allele frequency for haplotype in a wide range of breeds suggest widespread genetic progress in susceptibility to ovine lentivirus (OvLV) is possible with the TMEM154 genetic marker test, and the recessive mode of inheritance for the favorable haplotype 1 creates a tradeoff for producers between rapid genetic gain at higher cost, or somewhat slower gain at lower cost
Intervention strategies for SRLV based on host genetics and genomics have great promise that is only beginning to be fulfilled
Summary
Small ruminant lentiviruses (SRLV) were defined by infection and disease in host species, sheep and goats. Production losses for producers stem from early lamb mortality [16], lower lamb weights in older infected ewes [16,17], estimated early culling approximately 1 year prior to uninfected animals [18], and export restrictions [12] All of these contribute to the high economic cost of OvLV [19,20]. Economic losses are due to reduced milk yield, mastitis, interaction with bacterial mammary infection, and premature culling [22,23,24,25] Both OvLV and CaLV show evidence of breed differences in susceptibility [26,27,28,29,30,31,32,33,34], that together with other evidence [35,36,37,38,39] suggest a host genetic component in susceptibility and control
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