Genetic Characterization of Small Ruminant Lentiviruses (SRLVs) Circulating in Naturally Infected Sheep in Central Italy

Abstract

Small ruminant lentiviruses (SRLVs) represent a very heterogeneous group of ss-RNA viruses that infect sheep and goats worldwide. They cause important, deleterious effects on animal production and limit the animal trade. SRLVs show a high genetic variability due to high mutation rate and frequent recombination events. Indeed, five genotypes (A-E) and several subtypes have been detected. The aim of this work was to genetically characterize SRLVs circulating in central Italy. On this basis, a phylogenetic study on the gag-pol genetic region of 133 sheep, collected from 19 naturally infected flocks, was conducted. In addition, to evaluate the frequency of mutation and the selective pressure on this region, a WebLogo 3 analysis was performed, and the dN/dS ratio was computed. The results showed that 26 samples out of 133 were clustered in genotype A and 106 samples belonged to genotype B, as follows: A9 (n = 8), A11 (n = 10), A24 (n = 7), B1 (n = 2), B2 (n = 59), and B3 (n = 45). No recombination events were found. Mutations were localized mainly in the VR-2 region, and the dN/dS ratio of 0.028 indicated the existence of purifying selection. Since the genetic diversity of SRLVs could make serological identification difficult, it is important to perform molecular characterization to ensure a more reliable diagnosis, to maintain flock health status, and for the application of local and national control programs.

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

“…A previous study in our country analyzed shorter amino acid sequences, including only epitope 2 and the MHR [ 24 ], without, however, comparing the specific regions of epitopes, instead comparing the total amino acid sequences. Our findings confirmed the presence of the asparagine-valine “NV” and the double glycine “GG” motifs clustered in genotypes A and B, respectively, as previously described in similar studies [ 34 , 39 , 49 , 54 , 60 , 61 ]. Also, epitopes 2 and 3 were found highly conserved when the strains of genotype A from the present study were compared to the reference strains of the same clade, with the exception of one isolate (s-42fl) in which three new amino acid replacements were identified [one conservative substitution in epitope 2 (D/E) and two non-conservative substitutions in epitope 3 (G/R and Y/S)].…”

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

“…An infection with a genetically divergent MVV strain that is different from the MVV strain(s) circulating in the other flocks could be the reason for this particular flock's seroprevalence. Indeed, recent genetic and epidemiological studies, conducted in Italy identified at least three genotypes and great variability of subtypes, even inside the same flock [13,14].…”

“…Like other viral diseases, there is no treatment against SRLV infections. The SRLV's genetic variability, constantly enlarged by descriptions of new circulating genotypes and subtypes [12][13][14], contributes to making all efforts for the development of vaccines inconclusive. The eradication programs are expensive but remain the foremost sustainable approach to reducing SRLV infection in the small ruminant industry.…”

Isolation and Identification of Caprine Arthritis Encephalitis Virus from Animals in the Republic of Mordovia

“…To this end, it would be appropriate to draw the attention of owners who still underestimate this serious problem to a proper assessment of the state of animal health [41]. Serological screening together with a rigorous evaluation of the flock may greatly reduce the risk of infection.…”