Accurate Diagnosis of Small Ruminant Lentivirus Infection Is Needed for Selection of Resistant Sheep through TMEM154 E35K Genotyping

Abstract

Small ruminant lentiviruses (SRLV) cause an incurable multiorganic disease widely spread in sheep and goats that disturbs animal welfare and production. In the absence of a vaccine, control measures have been traditionally based on early diagnosis and breeding with virus-inactivated colostrum with segregation of seropositive animals. However, antigenic heterogeneity, poor antibody production due to low viral load, and single strain design of most available ELISA, pose a threat to SRLV diagnosis. Genome-wide association studies have described TMEM154 E35K polymorphism as a good genetic marker for selection of resistant animals in some American and European breeds. In this study, a multitargeted serological and virological screening of more than 500 animals from four different breeds (latxa, raza Navarra, assaf, and churra) attending to SRLV infection status was performed. Then, animals were genotyped to characterize TMEM154 E35K polymorphism. ELISA procedures, individually considered, only identified a proportion of the seropositive animals, and PCR detected a fraction of seronegative animals, globally offering different animal classifications according to SRLV infection status. TMEM154 allele frequency differed substantially among breeds and a positive association between seroprevalence and TMEM154 genotype was found only in one breed. Selection based on TMEM154 may be suitable for specific ovine breeds or SRLV strains, however generalization to the whole SRLV genetic spectrum, ovine breeds, or epidemiological situation may need further validation.

First Survey of SNPs in TMEM154, TLR9, MYD88 and CCR5 Genes in Sheep Reared in Italy and Their Association with Resistance to SRLVs Infection

“…Genetic variations that generate amino acid substitutions gave rise to 15 different and unambiguous haplotypes that included 100% of the observed ones as a result of the presence of only one polymorphic site in heterozygosity. Specifically, we identified six already known (1, 2, 3, 4, 6, 16) and nine novel haplotypes (17)(18)(19)(20)(21)(22)(23)(24)(25) reported in Table S1.…”

“…TMEM154 gene encodes for a precursor protein of 191 amino acids that mature in a protein of 161 amino acids, but its biological function is still unknown. Some studies showed that the amino acid substitution glutamate tolysine (E/K) in position 35 (rs408593969) can modulate the predisposition to the infection, in particular the KK genotype is associated to a decrease in susceptibility together with low serological levels [ 9 , 15 , 16 , 17 , 18 , 19 ]. However, other authors reported that the KK genotype is not fully protective depending on several possible factors as viral dose, route of infection, type and number of SRLVs strains involved, comorbidities, other environmental and genetic factors [ 14 , 19 ].…”

Transcriptome Analysis for Genes Associated with Small Ruminant Lentiviruses Infection in Goats of Carpathian Breed

“…Several attempts to identify host factors associated with resistance to SRLV infections have been made, and some loci were identified [11][12][13][14][15]. In particular TMEM154 gene (transmembrane protein 154), TMEM38A (transmembrane protein 38A), CCR5 (chemokine(C-C motif) receptor type 5), MHC (major histocompatibility complex), ZNF389 (zinc-finger protein 389), TLRs (toll-like receptors), APOBEC3 (apolipoprotein B editing complex 3), TRIM5 (tripartite motif protein 5 alpha), Tetherin/BST-2 (bone marrow stromal cell antigen 2) and other cytokines (interleukin 2 (IL2), interleukin 2 receptor (IL2R), tumor necrosis factor alfa (TNF-α), interleukin 4 (IL4), interleukin 8 (IL8), interleukin 6 (IL6), interleukin 16 (IL-16), interferon gamma (IFN-γ), transforming growth factor beta (TGF-β1), monocyte chemoattractant protein-1 (MCP-1), granulocyte-macrophage colony-stimulating factor (GM-CSF)) and chemokine ligands (C-C motif ligand 2 (CCL2), C-C motif ligand 5 (CCL5), C-C motif ligand 20 (CCL20)) seem to have an important role in the SRLV infection susceptibility/resistance [12,13,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. However, additional studies are still necessary to learn more about genes involved in SRLV immunity.…”

Serological, Molecular and Culture-Based Diagnosis of Lentiviral Infections in Small Ruminants

“…Therefore, except for the impediments arising from virus nature and the immunopathological mechanisms, a critical endeavor for the enhancement of serological diagnosis performance is to enrich the antigenic design of ELISA and improve its negative predictive value. The use of whole virus, incorporation of multiple antigens and synthetic peptide combinations, and genotype-specific immunodominant epitopes have been proposed for the extension of the antigenic spectrum and the amplification of the detection capacity of the assay [54,[56][57][58]60,62,63].…”

“…A “gold standard” test with high values of sensitivity, specificity and accuracy, blindly used in every case does not seem readily feasible when considering the special characteristics of SRLVs (i.e., high genetic variability, mechanisms of virus replication, and animal humoral immune response). Nonetheless, the scientific community has addressed these limitations, proposing targeted combinations of diagnostic tools, which are constantly evaluated to reduce the possibility of both newly or persistently infected animals to evade diagnosis [ 27 , 39 , 62 , 63 , 70 , 82 , 86 , 101 , 102 ]. Although combination of diagnostics increases cost, time, and the effort required, it seems to be inevitable for the early and safe diagnosis in young animals which are likely infected but seronegative.…”