Genetic factors put some foals at increased risk of contracting potentially deadly pneumonia, researcher at Texas A&M University have found.
Pneumonia caused by Rhodococcus equi is a common cause of disease and death in foals.
The team of nine researchers said while environmental factors contributed to the incidence of the disease, genetic factors that could influence the clinical outcomes of R. equi infection were ill-defined.
Recent evidence suggested some horses may be genetically predisposed to the condition, they said.
Their study focused on a large Texas quarter horse breeding farm where foals bred in 2011 were categorized into three groups – 43 with R. equi pneumonia, 156 foals with ultrasonographic evidence of pulmonary lesions that never developed clinical signs of pneumonia, and 49 foals that had no clinical signs or ultrasonographic evidence of pneumonia.
From each group, 24 foals were randomly selected for genetic testing.
They found a region on chromosome 26 that had moderate evidence of association with R. equi pneumonia when comparing clinical and subclinical foals.
A joint analysis including all study foals revealed a three to four-fold increase in the odds of disease for a homozygous SNP within the associated region when comparing the clinical group with either of the other two groups of foals or their combination.
Their findings, published in the open-access journal, PLoS ONE, provided evidence that genetic factors may indeed contribute to R. equi pneumonia in foals.
“Identifying the genetic and biological basis of susceptibility, or perhaps resistance, to R. equi pneumonia in foals is important, because it might lead to the development of diagnostic and therapeutic tools to manage at-risk foals on breeding farms and might shed light on critical host defense mechanisms,” they said.
The researchers said they failed to identify a significant association with candidate genes previously associated with R. equi pneumonia in other breeds of foals in other studies.
This, they said, may have been attributable to differences among populations of foals studied, such as breeds, or study methods.
Nevertheless, what was common among these studies was the identification of genes pertaining to host defenses against infectious pathogens.
It was conceivable, they said, these apparently discrepant findings may ultimately converge on critical biological pathways or processes that could influence susceptibility to infection with R. equi and other pathogens.
McQueen CM, Doan R, Dindot SV, Bourquin JR, Zlatev ZZ, et al. (2014) Identification of Genomic Loci Associated with Rhodococcus equi Susceptibility in Foals. PLoS ONE 9(6): e98710. doi:10.1371/journal.pone.0098710
The full study can be read here.