Rotavirus A is a pesky little organism that causes problems for most pig farmers across Nebraska and around the country. Despite decades of research on the topic, pigs are still highly likely to contract the virus at some point in their lifetimes.
However, a team of researchers at the University of Minnesota — led by doctoral candidate Frances Shepherd in the College of Veterinary Medicine — are working on getting to the root cause of the problem.
Pig farmers who have to deal directly with the rotavirus know it causes diarrheal disease in their animals. While it doesn’t get the news coverage that the African swine fever virus does these days, it’s still quite common in pigs and hits pork producers directly in their pocketbooks.
“The biggest impact on hog production is weight loss and failure for animals to thrive,” Shepherd said. “Ultimately, that will cause producers to suffer potentially extensive economic loss. The virus is also very hard to get rid of on pig farms.”
The doctoral candidate said rotaviruses are “sturdy” viruses and they tend to affect piglets the most out of any age group. She said rotaviruses like to “hang out” and replicate themselves in the small intestines of pigs, which is not a good spot for piglets.
“Compared to older animals, the piglets’ small intestines can’t regenerate themselves fast enough to fight it off,” she said. “When piglets are first born, they suckle for roughly three weeks and rely on the antibodies they get from the mother’s milk to fight diseases. As the antibodies from the milk travel through the GI tract, they bind to the rotaviruses and prevent infection.”
It’s fecal-orally transmitted to the piglets because it’s in the environment. The most common way pig producers typically immunize piglets is with “natural planned exposure.” Material containing a live virus from the farm is mixed in with feed, which the sows then consume. It doesn’t make the mothers sick, but it does boost their immune systems.
“Producers prefer this method of stimulating immunity in their animals because it deals with the rotavirus strains that are specific to their farm,” Shepherd said. “Producers often prefer the feedback method of immunizations to commercial vaccines, which don’t always cover virus strains that are prevalent at a given time on their operation.”
So, the question is, why are pigs still highly likely to get rotavirus at least once in their lives with treatment methods available? Shepherd and her study teammates are finding out that viruses can adapt over time, which can help them escape treatment methods on the farm.
“If it’s a different kind of rotavirus, that’s an easy question to answer,” she said. “If there are just a few genetic changes to the virus, that’s a more difficult question. That’s the knowledge gap we’re trying to fill with the research we are doing here.”
Her team is hoping to identify the specific parts of the rotavirus that interact with a pig’s immune system.
“When those parts change, that’s how the virus will escape recognition from the immune system,” Shepherd said.
A native of Madison, Wisconsin, Shepherd said viruses change all the time as they replicate and transmit between different hosts. Even the replicating process itself isn’t “super-accurate” and changes can happen naturally through the process. While existing immunity has something to do with changes in the rotavirus, Shepherd said a lot of it is random.
The research team is using a computer-model approach to try to figure out where the viruses interact with the immune system. Computer models help them predict which sites of the virus structure are most likely to interact with antibodies.
As the work continues, the long-term goal of the study is to help the pork industry come up with better vaccines for rotavirus. While most producers like the way that natural planned exposure can be tailored to their farm, she said using a live virus can be a bit of a “messy process”
Instead, if the researchers can figure out what parts of the virus are most vulnerable to the immune system, that will help scientists design vaccines to specifically target those sites. The other goal they want to accomplish is to develop the ability to tell producers to watch for certain changes in the rotavirus on their farms — information that producers could use to update their feedback control efforts.
“Natural planned exposure uses a live virus to induce immunity,” Shepherd said. “That’s great, but there are also piglets in those sows that will be born soon, and you don’t want those piglets around a live virus. We’re hoping to be able to put something else in a syringe that will induce immunity and not be a health risk to other animals, especially piglets.”
She’s optimistic that the project will get to its goal due to one specific reason — the technology is already available for other pathogens.
“Merck Animal Health already has the technology that will allow producers to put the influenza virus they may be dealing with on their farm directly into a vaccine,” she said. “Getting to that point with rotavirus is certainly within our grasp.”