Loci Associated With Antibody Response in Feral Swine (Sus scrofa)Infected With Brucella suis

Authors: PIERCE, COURTNEY - Colorado State University; BROWN, VIENNA - Colorado State University; Olsen, Steven; Boggiatto, Paola; PEDERSEN, KERRI - Colorado State University; Miller, Ryan; SPEIDEL, SCOTT - Colorado State University; SMYSER, TIMOTHY - Colorado State University

Submitted to: Frontiers in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/23/2020
Publication Date: 11/25/2020
Citation: Pierce, .F., Brown, V.R., Olsen, S.C., Boggiatto, P.M., Pedersen, K., Miller, R.S. Speidel, S.E., Smyser, T.J. 2020. Loci associated with antibody response in feral swine (Sus scrofa)infected with Brucella suis. Frontiers in Veterinary Science. 7. https://doi.org/10.3389/fvets.2020.554674.
DOI: https://doi.org/10.3389/fvets.2020.554674

Interpretive Summary: Populations of invasive feral swine (Sus scrofa) are now established in the majority of U.S. states. Feral swine disrupt ecosystems, damage crops, and carry zoonotic pathogens including Brucella suis – the causative organism for brucellosis. Brucellosis serologic tests are not sensitive in swine as they frequently do not develop antibody responses even when infected. Contact with infected feral swine poses spillover risks to domestic pigs as well as humans, companion animals, wildlife, and other livestock. Genetic factors influence the outcome of infectious diseases; therefore, genome wide association studies (GWAS) of differential immune responses can provide insight into disease dynamics. In this study genes related to immune responses were compared between seropositive and seronegative feral swine which were naturally-infected with B. suis. Nine putative candidate genes associated with differences in seroconversion were identified on chromosome 8, 9, 10, 12, and 18. This work identified nine genes that may play a role in influencing serologic responses to brucellosis infection and provides a scientific explanation for the observed lack of seroconversion in infected swine. This work will be of interest to brucellosis researchers, regulatory personnel, and producers for its implications not only related to brucellosis, but also for understanding immune responses to other pathogens of swine.

Technical Abstract: Populations of invasive feral swine (Sus scrofa) are now established in the majority of U.S. states. Feral swine disrupt ecosystems, damage crops, and carry zoonotic pathogens including Brucella suis – the causative organism for brucellosis. In domestic swine, brucellosis results in reproductive failure due to abortions and infertility. Contact with infected feral swine poses spillover risks to domestic pigs as well as humans, companion animals, wildlife, and other livestock. Genetic factors influence the outcome of infectious diseases; therefore, genome wide association studies (GWAS) of differential immune responses among feral swine can provide an understanding of disease dynamics and inform management to prevent the spillover of brucellosis from feral swine to domestic pigs. We sought to identify quantitative trait loci (QTL) associated with differential immune responses among feral swine naturally-infected with B. suis using a case-control GWAS. Tissue, serum, and genotype data (68,516 bi-allelic single nucleotide polymorphisms) were collected for 47 feral swine at two Texas abattoirs. The 47 feral swine were culture positive for Brucella spp. and, of these, 16 were antibody positive (cases) and 31 were antibody negative (controls). Single-locus GWAS were performed using efficient mixed-model association eXpedited (EMMAX) methodology with three genetic models: additive, dominant, and recessive. Eight loci associated with seroconversion were identified on chromosome 8, 9, 10, 12, and 18. Subsequent bioinformatic analyses revealed nine putative candidate genes related to immune function, most notably phagocytosis and induction of an inflammatory response. Identified QTL may play an important role in host immune responses to B. suis infection, characterized by a detectable bacterial presence yet a differential antibody response. Additional studies are necessary to fully understand the genetic component of the response to B. suis infection and to translate understanding to inform management decisions for disease control.