This study was carried out to evaluate the performance of Brazilian Somalis sheep to natural infections by gastrointestinal nematodes. During 98 days, 75 weaned sheep, initially 3-4 months old, were kept on the same pasture and evaluated. Fecal and blood samples were collected for parasitological and hematological exams. After this period, the eight most resistant and the eight most susceptible animals were selected based on their individual averages of nematode fecal egg counts and were slaughtered for worm burden determination and nematodes identification. Abomasum and abomasum lymph nodes were also recovered for gene expression analysis. The animals selected as resistant had lower fecal egg counts during experimental period and smaller worm burdens than the susceptible ones (P < 0.05). The genus Haemonchus, followed by Trischostrongylus and Oesophagostomum, were identified in composite cultures. Haemonchus contortus was the specie identified in the abomasum. Packed cell volume and total plasma protein means were higher in the resistant group (27.2% and 6.1 g/dL) than in the susceptible one (22.5% and 5.3 g/dL), respectively. Regarding cytokine gene expression, IL-4 (P < 0.05) was up-regulated in the abomasum of resistant animals and TNF-α (P < 0.03) and IFN-γ (P < 0.03) in susceptible ones. In abomasum lymph nodes, IL-4 (P < 0.04) and IL-13 (P < 0.05) were up-regulated in the resistant animals and IFN-γ in the susceptible one (P < 0.01). This work provides further evidence that, within a given animal breed, individuals have different responses when infected by gastrointestinal nematodes. Resistant animals who responded more quickly and efficiently to these infections activated a TH2-type response.
Small ruminant lentiviruses (SRLVs) are prevalent in North American sheep and a major cause of production losses for the U.S. sheep industry. Sheep susceptibility to SRLV infection is influenced by genetic variation within the ovine transmembrane 154 gene (TMEM154). Animals with either of two distinct TMEM154 haplotypes that both encode glutamate at position 35 of the protein (E35) are at greater risk of SRLV infection than those homozygous with a lysine (K35) haplotype. Prior to this study, it was unknown if TMEM154 associations with infection are influenced by SRLV genetic subgroups. Accordingly, our goals were to characterize SRLVs naturally infecting sheep from a diverse U.S. Midwestern flock and test them for associations with TMEM154 E35K genotypes. Two regions of the SRLV genome were targeted for proviral amplification, cloning, sequence analysis, and association testing with TMEM154 E35K genotypes: gag and the transmembrane region of env. Independent analyses of gag and env sequences showed that they clustered in two subgroups (1 and 2), they were distinct from SRLV subtypes originating from Europe, and that subgroup 1 associated with hemizygous and homozygous TMEM154 K35 genotypes and subgroup 2 with hemi- and homozygous E35 genotypes (gag p < 0.001, env p = 0.01). These results indicate that SRLVs in the U.S. have adapted to infect sheep with specific TMEM154 E35K genotypes. Consequently, both host and SRLV genotypes affect the relative risk of SRLV infection in sheep.
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