Identification of QTL affecting resistance/susceptibility to acute Actinobacillus pleuropneumoniae infection in swine

Abstract

Actinobacillus pleuropneumoniae is among the most important pathogens worldwide in pig production. The agent can cause severe economic losses due to decreased performance, acute or chronic pleuropneumonia and an increased incidence of death. Therapeutics cannot be used in a sustainable manner, and vaccination is not always available, but discovering more about host defence and disease mechanisms might lead to new methods of prophylaxis. The aim of the present study was to detect quantitative trait loci (QTL) associated with resistance/susceptibility to A. pleuropneumoniae. Under controlled conditions, 170 F2 animals of a Hampshire/Landrace family, with known differences in founder populations regarding A. pleuropneumoniae resistance, were challenged with an A. pleuropneumoniae serotype 7 aerosol followed by a detailed clinical, radiographic, ultrasonographic, pathological and bacteriological examination. F2 pigs were genotyped with 159 microsatellite markers. Significant QTL were identified on Sus scrofa chromosomes (SSC) 2, 6, 12, 13, 16, 17 and 18. They explained 6-22% of phenotypic variance. One QTL on SSC2 reached significance on a genome-wide level for five associated phenotypic traits. A multiple regression analysis revealed a combinatory effect of markers SWR345 (SSC2) and S0143 (SSC12) on Respiratory Health Score, Clinical Score and the occurrence of death. The results indicate the genetic background of A. pleuropneumoniae resistance in swine and provide new insights into the genetic architecture of resistance/susceptibility to porcine pleuropneumonia. The results will be helpful in identifying the underlying genes and mechanisms.

Update onActinobacillus pleuropneumoniae-knowledge, gaps and challenges

“…The fact that more than 50 App genes are involved in iron uptake and metabolism (Xu et al., ), some of which are differentially expressed during infection (Deslandes et al., ; Klitgaard, Friis, Jensen, Angen, & Boye, ), supports the major importance of this bacterial adaptation strategy for disease pathogenesis (Bossé et al., ). Genetically defined differences in disease susceptibility between breeding lines were, in part, due to differences in the iron‐transport protein transferrin, because different protein variants might be bound with variable intensity by the transferrin binding receptors of App (Daniłowicz et al., ; Reiner, Bertsch, et al., ).…”

“…It was shown after experimental infection that a clinical respiratory health score was highly correlated to the severity of lung lesions, and that acute lung damage varies between pig breeding lines and was decisive for the course of disease (Hoeltig et al., ). Quantitative trait loci (QTL) associated with resistance were found on S. scrofa chromosome 2 (SSC2); candidate genes on SSC2 are IL‐9 and CD14 , which are involved in lung immunity and LPS recognition, respectively (Reiner, Bertsch, et al., ). Further, candidate genes on other chromosomes were members of the signal transducer and activator of transcription gene family, which, depending on the type of cytokine receptor that is activated during the infection, can selectively stimulate multiple signal pathways during the inflammatory response (Reiner, Dreher, et al., ).…”

“…An ambitious prevention strategy for the future is the development of genetic markers for selection of disease resistant pigs for breeding strategies. QTL on SSCs 2, 6, 12, 13, 16, 17 and 18, associated with resistance/susceptibility to App, were identified in controlled infection experiments in cross‐bred Hampshire/Landrace pigs and explained 6%–22% of variance in disease severity (Reiner, Bertsch, et al., ; Reiner, Dreher, et al., ). Another group found six QTL, also including SSCs 2, 12, 13 and 18, associated with dorso‐caudal chronic pleuritis (Gregersen et al., ).…”

Genetic resistance - an alternative for controlling PRRS?

“…However, the search for significant and applicable gene variants has developed into an ever-expanding and successful branch of clinical research, including viral (Pseudorabiesvirus [88]; Influenza A (e.g. [143]); bacterial (Haemophilus parasuis [131]; Actinobacillus pleuropneumoniae [93,94]; Mycoplasma hyopneumoniae (e.g., [108]); Streptococcus suis [136]) and parasitic diseases (Sarcocystis [89]; Ascaris suum [100,101]). More than 2,500 quantitative trait loci (QTL) have been published for health parameters in the pig, among them 400 for resistance/susceptibility against a broad range of pathogens (http://www.animalgenome.org/QTLdb/; current status: October 2016).…”

Candidate genes and gene markers for the resistance to porcine pleuropneumonia

“…Resistance to A. pleuropneumoniae has been described by different authors and in different pig breeds (Straw et al 1983;Jones 1986;Hoeltig et al 2009). Differences between lines of German Landrace and Hampshire pigs were used to map QTL for resistance to A. pleuropneumoniae in a F2 family, with the highest effects on SSC2 and SSC12 (Reiner et al 2014a), and to show associations between resistance and a broad range of differentially expressed genes (Reiner et al 2014b). The QTL identified in this study were in good agreement with those mapped in a study of slaughter pigs (Gregersen et al 2010).…”