By T. D. Thornton
Only weeks after making the preliminary identification that an entirely new rotavirus is responsible for the spate of diarrhea cases afflicting just-born foals this spring, researchers at the University of Kentucky's Maxwell H. Gluck Equine Research Center and the Veterinary Diagnostic Laboratory are in the process of fine-tuning a just-developed assay to differentiate this emerging threat from the better-recognized Rotavirus A first detected three decades ago.
This new strain has been dubbed Rotavirus B, and Dr. David Horohov, Gluck's director and the chairperson of the school's Department of Veterinary Science, told TDN Friday it is “likely, if not entirely, the cause for all the diarrheas we've been seeing.”
Horohov added that the prognosis is generally good for foals who have suffered through this new form of rotavirus during the first two to 14 days of their lives.
“Once you get the foal through the rough spot where it's having these difficulties, you can expect a sort of normal recovery and then normal growth by the foal,” Horohov said in a May 7 phone interview.
When diarrhea cases began mounting at central Kentucky's Thoroughbred farms in March, the Gluck team began to mobilize to better understand the extent and scope of this health threat, utilizing emergency funding to do so while also receiving financial support from the Kentucky Thoroughbred Owners and Breeders Foundation, the Grayson-Jockey Club Research Foundation, and Coolmore America.
Horohov said the initial identification was made by using a DNA sequencing technique called metagenomic analysis, which involves taking pool samples from numerous foals with diarrhea and examining the many genomes that are present to see if something familiar or different can be discerned. In this case, it was quickly determined that there was something genetically novel present.
The Gluck's diagnostic lab researchers then got to work, and within several weeks had developed a polymerase chain reaction test that would enable them to look at individual samples to determine if the new virus was present there.
“They've been sort of troubleshooting the assay and making it work, and right now we do have an assay that will allow us to identify the Rotavirus B,” Horohov said. “And it will differentiate it from the Rotavirus A so we know we're looking at the novel rotavirus.”
Horohov said that in preliminary studies of 43 individual samples collected from foals with a presumptive diagnosis of rotavirus-related diarrhea, 42 came back positive for Rotavirus B and the lone outlier was indeterminate.
“So it looks like the test is, in fact, accurate,” Horohov said. “They are doing some subsequent testing against known negatives and some other samples to make sure that it is exactly what we think it is. But based on that preliminary data, looking at a collection of samples from different farms, all of them foals with the same basic pattern, it's pretty clear that this is indeed the Rotavirus B that we are dealing with.”
As for the extent and trajectory of Rotavirus B in Kentucky right now, Horohov said that's difficult to pinpoint.
“We're having a relatively limited view of that right now because we're really only working with selected farms [that are providing the samples],” Horohov said. “We're not getting large numbers of samples coming into the diagnostic labs since the test isn't ready yet for use by the public, [so] we don't really have a way to monitor that.
“[But] word of mouth is that again, it's showing the pattern we saw before, where some farms were having a significant problem with it whereas other farms were either having minimal problems or, more importantly, those that took the steps to increase their biosecurity-including things like having the foals born outside and minimal handling of the foals-seem to have gotten a better handle on this,” Horohov said.
“There seems to be more control going on than there was [at the start of the outbreak],” Horohov said. “A lot of the farms, fortunately, seem to have found ways to reduce the problem.”
Horohov said the Gluck researchers also looked at whether the diarrhea outbreak might have been caused by a bacterial problem, but that “all of the data that we have right now indicates that is not the primary cause of this.”
Horohov said that the concern with Rotavirus B is “typical of any diarrheal disease. There's fluid loss associated with that. There's also a loss of ions. So the foals, particularly given their young age, rapidly become metabolically challenged by this. As a result of that, the therapy that's given to them is primarily supportive, and typically it's quite successful.”
Horohov summed up: “This is similar to what we saw originally when the Rotavirus A variant first appeared. We were seeing that going back into the 1990s. As long as you get the foals through this period and you replace that fluid loss and keep your ions in check, normally they come out of it okay. There is always a risk that you may have secondary issues that occur, [but] certainly these foals will be watched carefully to make sure none of those issues show up.”