As pollsters have learned the hard way, prediction can be fraught with peril. When dealing with a disease as destructive as PRRSV (Porcine Reproductive and Respiratory Syndrome virus), however, science needs every edge it can get. To that end, one researcher on the Genome Alberta-led project to increase disease resilience in pigs through genomics is examining a biomarker that could predict PRRSV severity.
“One of the keys to battling PRRSV is identifying which pigs are susceptible to the virus and which are resilient, meaning they are only mildly affected,” said Dr. John Harding, Professor, Department of Large Animal Clinical Sciences at the Western College of Veterinary Medicine, University of Saskatchewan.
“We know that PRRSV infects pigs via a receptor called CD163, which is shed and released into the bloodstream. Our hope is that the bio-marker sCD163 will help predict how severely pigs are affected by the virus.”
Of course, progress on any front requires large data sets, so researchers accessed numerous blood samples from three experiments to gauge the level of sCD163 in a range of animals: pigs challenged with severe PRRSV, pigs challenged with PRRSV and other diseases, and healthy pigs. They then explored whether a correlation exists between sCD163 levels in blood and disease severity or resilience in PRRSV-infected pigs.
Though a significant relationship has not yet been found, scientists gained some valuable insights to aid in future research.
Shedding light on disease
One of the key findings was that sCD163 levels decreased from weaning to the mid-grower stage, at which point they stabilized. There were no changes detected among parities or stages of gestation, but an interesting note is that as sows get older, it appears some of them have the ability to shed more CD163 into serum.
“When we get into PRRSV infection trials in nursery pigs affected at 28 days of age, the reason there is no shedding response at that age is that pigs already have high levels of sCD163 in their blood,” said Dr. Harding. “It’s almost like the capacity to shed is not there because they have already shed so much.”
As sCD163 levels decrease with age, scientists believe a pig’s ability to shed will increase, and that PRRSV causes an acute shedding response, except in weaned pigs where the sCD163 levels are already high.
It also appears there may be an association between shedding amounts and average daily gain, and a possible connection between CD163 and either treatment levels or incidence of mortality. In both cases, more analysis is needed for confirmation.
In the meantime, researchers remain optimistic about the potential impact of future findings around CD163.
“If we can develop proof of concept that CD163 is a measure of resilience and/or susceptibility, it would support further investigation in this area. We could look at genotypic and phenotypic associations to find if there are genetic markers that can be used to pinpoint animals with high or low CD163 shedding response. This all relates to the ability of science to select animals that are genetically superior based on disease response, and sCD163 is one biomarker in the blood that could be indicative of that response.”
Though sCD163 is a promising avenue, it’s by no means the only one being explored. Science is casting a wide net when it comes to biomarkers, and regardless of where it takes them, the goal is the same.
“We aim to identify a simple, effective and inexpensive tool to support the pork sector in its quest for disease resilient pigs that can better combat PRRS and other diseases affecting breeding and feeding herds.”
Foretelling the future can be tricky, but if science finds such a tool, the response by industry isn’t hard to predict.