Abstract
BackgroundSalmonella infection is a serious concern in poultry farming because of its impact on both economic loss and human health. Chicks aged 20 days or less are extremely vulnerable to Salmonella pullorum (SP), which causes high mortality. Furthermore, an outbreak of SP infection can result in a considerable number of carriers that become potential transmitters, thus, threatening fellow chickens and offspring. In this study, we conducted a genome-wide association study (GWAS) to detect potential genomic loci and candidate genes associated with two disease-related traits: death and carrier state.MethodsIn total, 818 birds were phenotyped for death and carrier state traits through a SP challenge experiment, and genotyped by using a 600 K high-density single nucleotide polymorphism (SNP) array. A GWAS using a single-marker linear mixed model was performed with the GEMMA software. RNA-sequencing on spleen samples was carried out for further identification of candidate genes.ResultsWe detected a region that was located between 33.48 and 34.03 Mb on chicken chromosome 4 and was significantly associated with death, with the most significant SNP (rs314483802) accounting for 11.73% of the phenotypic variation. Two candidate genes, FBXW7 and LRBA, were identified as the most promising genes involved in resistance to SP. The expression levels of FBXW7 and LRBA were significantly downregulated after SP infection, which suggests that they may have a role in controlling SP infections. Two other significant loci and related genes (TRAF3 and gga-mir-489) were associated with carrier state, which indicates a different polygenic determinism compared with that of death. In addition, genomic inbreeding coefficients showed no correlation with resistance to SP within each breed in our study.ConclusionsThe results of this GWAS with a carefully organized Salmonella challenge experiment represent an important milestone in understanding the genetics of infectious disease resistance, offer a theoretical basis for breeding SP-resistant chicken lines using marker-assisted selection, and provide new information for salmonellosis research in humans and other animals.
Highlights
Salmonella infection is a serious concern in poultry farming because of its impact on both economic loss and human health
Mortality rates for the Rhode Island Red (RIR), Beijing You (BY), and Dwarf Chicken (DW) chicks reached 25.1, 8.3, and 22.7%, respectively, and the corresponding carrier-state levels in the spleens were equal to 17.9, 0.6, and 15.8%, which indicate that BY chicks are more resistant to Salmonella pullorum (SP) infection than DW and RIR chicks
Runs of homozygosity We found that FROH did not differ between the traits analyzed here (Fig. 6), but the DW and BY chicks that died of SP infection showed the lowest values
Summary
Salmonella infection is a serious concern in poultry farming because of its impact on both economic loss and human health. Pullorum disease is an acute poultry infectious disease that is caused by the chicken-restricted facultative intracellular gram-negative bacterium, Salmonella pullorum (SP) This disease usually results in high mortality of chicks less than 20 days old, especially in developing countries where cleaning and disinfection procedures are usually not effective [2]. SP infection generally leads to three disease outcomes: the most susceptible birds die within about 2 to 20 days showing typical SP infection symptoms such as hepatosplenomegaly, white diarrhea and cecal cores [3]; some chicks survive by clearing the pathogen through a series of immune responses; and other chicks develop a carrier state with SP present in their splenic macrophages for a long period of time [4]. These carriers can transmit the pathogen to other chickens horizontally or to their offspring via the eggs [5]
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