Foals are born with naive immune systems and derive immediate antibody protection from colostrum, the first milk produced by their mother. Equine Rotaviruses are highly contagious, causing life-threatening diarrheal disease that typically only affects foals, not adult horses.
Typically, the younger the foal, the more severe the clinical signs. Until recently, Rotavirus A was our only concern for horses, but recently Equine Rotavirus B was identified. Like Rotavirus A, Rotavirus B has been detected in the feces of affected foal’s moms, but whether it is passing through or being amplified by the mare has yet to be determined.
Equine Rotavirus A is better-studied and has had a vaccine for pregnant mares (which helps pass immune protection on to the foal) for over 30 years, however, the new strain of Equine Rotavirus B threw a wrench in the cog of foal health care having been discovered just four years ago.
Luckily, there are researchers who are committed to finding a solution to help mitigate the impacts of Equine Rotavirus B. We sat down with Dr. Emma Adam, to discuss the ins and outs, as well as the future of rotavirus research.
Dr. Adam currently works at the Gluck Equine Research Center at the University of Kentucky, and has years of experience serving the equine industry as a highly distinguished veterinarian.
Q: How Did Equine Rotavirus Become One Of Your Specialities?
Dr. Adam: In 2021, I was hearing about a lot of neonatal diarrhea that was affecting every single foal on specific farms. There are very few things that can actually do that to a newborn foal, especially under the high health standards that we have amongst our Thoroughbred and Standardbred breeding stock in Kentucky.
Some people thought it was Clostridium perfringens (C. Perfringens) because a lot of the foals were testing positive for that disease associated pathogen, but we know that true Clostridiosis doesn't go through every single foal, one after the other. In addition, foals with Clostridiosis tend to be much sicker with signs of systemic disease and cardiovascular compromise.
I began investigating and noticed that the pattern was very distinct. These farms had multiple healthy foals born, and then one foal would get sick and then every foal after that one would develop the same signs: watery diarrhea. It looked like a contagious issue and some foals were Clostridium perfringens positive, while others were negative. They were all Rotavirus A negative, which was the only rotavirus that we had on our radar at the time.
So, in collaboration with our terrific farm managers and veterinarians, I obtained samples and brought them to my colleagues for metagenomic sequencing. Using this cutting edge technology, we identified a new virus that we termed, Equine Rotavirus B, which had never been identified in horses.
What Are the Differences Between Rotavirus A and B? What are the Signs?
Today, we don't see Rotavirus A very often if broodmares have been appropriately vaccinated with the currently available vaccine.
Rotavirus B produces the same clinical signs as Rotavirus A infection. Foals can get sick as early as 12 hours of age but typically at 2 to 3 days of age, when they develop profuse, watery diarrhea. They will often experience abdominal distension, particularly if they get sick under 24 hours of age. They get colicky as a result of gut stasis and distension. As a result of massive fluid loss in the lumen of the intestine, these foals get severely dehydrated, and with the electrolyte and acid-base derangements they experience, without rapid and aggressive veterinary medical intervention, they can die .
We also observe that the younger the foal, the more severe the clinical signs, but we do not believe there is a difference between the disease process of Rotavirus A and B on the foal.
Remember, foal rotavirus can be a fatal disease. Today, we are very proactive in treating these foals, but back in the '80s before the vaccine, we saw a lot of foal deaths from this disease. That is why you have to get on top of these sick foals quickly and aggressively.
Where Does Rotavirus in Horses Come From?
The exact epidemiology of the virus is not something that we have a good handle on. We have not put money into investigating this because all of our money has been focused on developing a protective vaccine. We've done some limited studies where we certainly can detect it in mares that have sick foals or who have had sick foals.
We do know that rotaviruses hang out in the environment. In a recent study we published, we detected the virus in water troughs, puddles, and mud, in and around barns on farms that have been affected by the disease. Rotavirus A will hang around for about 9 months. We have not done similar testing for B at this time.
It's actually a very difficult virus to kill with disinfectants because it does not have a capsule. Viruses that have capsules on them are much more susceptible to things like detergents, so they're easier to kill. It takes usually 30 minutes of wet contact with an appropriate disinfectant at an appropriate dilution to inactivate the virus. And it's extremely contagious. If you extrapolate from studies done in other species, there is a suggestion that as few as 1,000 virus particles can infect and cause disease in a susceptible animal. When you consider that number to the billions of virus particles in one teaspoon of diarrhea - it’s pretty daunting.
How Much Do We Know About Rotavirus B?
While Rotavirus B is a much less researched group of rotaviruses, we do not have any reason to believe that it is exceptionally different to Rotavirus A in its pathology, but we don’t exactly know.
This means that, just like Rotavirus A, Equine Rotavirus B virus depletes the gut’s ability to digest the milk in the gut. As a result, we see both maldigestion (trouble breaking down food into absorbable nutrients) and osmotic diarrhea (when poorly digested substances in the intestines cause water to be drawn into the gut). We suspect that these conditions then set the gut up for an overgrowth of opportunistic organisms – of which Clostridium perfringens is a perfect example.
How Does Foal Rotavirus Impact the Gut Microbiome?
While we do not conclusively understand how these viruses affect the gut microbiome, we can make some assumptions based on the fact that foals are just starting to colonize their gut (they come into the world with a “blank” microbiome).
It is possible that you'll get an overgrowth of other bacteria (like C. perfringens) because rotavirus infection annihilates the digestive capacity of the gut, potentially allowing opportunistic bacterial overgrowth.
Secondly, when foals get rotavirus, we treat them with antimicrobials because we don't want that damaged and inflamed gut to be the source of translocation of enteric bacteria across the gut wall and into circulation. The use of antimicrobials will impact the development of their nascent microbiome.
How is Rotavirus Transmitted?
Rotavirus is transmitted via a fecal-oral route. It is important to understand that feces and manure are everywhere.
You don't necessarily know that you've got feces on your hands or your clothes or the stall door, but it is basically everywhere. This is why not touching foals, hand washing, and wearing and changing gloves is so important.
Given That Rotavirus A Has a Vaccine and Rotavirus B Does Not, How Can We Best Help Foals With No Rotavirus B Antibodies?
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If you are foaling out mares, you definitely need to make sure they're vaccinated against Rotavirus A. We have found that 3 vaccinations in each and every pregnancy are important here and cannot be skipped.
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Reduce contact with your foals. Because human contact is the way that the virus is likely best spread, the most important thing is to not touch your foals. In areas where we have identified Rotavirus B, this has helped. So, mares foal outside where humans can be there to assist with foaling, but wear protective equipment (Tyvek suits, boot covers or dedicated cleaned footwear, and gloves), do a Day 1 examination and IgG check, and then essentially do not touch the foal for the next 5 to 7 days.
Many breeders are using biothermal microchips so that they can do hands-free temperature taking. Careful observation of the mare and foal’s behavior, observing nursing behavior and looking at the mare’s udder to make sure the foal is nursing is really important.
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Practice hygiene when cleaning and mucking stalls. A lot of people will use a leaf blower to clean the passageway in a barn after they've cleaned the barn. It turns out that that is the most perfect way to spread pathogens all over the barn. Ditch the leaf blower, those are a bioterrorist's dream. Find more biosecurity information in this video and this article.
What Are the Economic Implications of Rotavirus?
First, it can mean an expensive veterinary bill. If the foal is treated on the farm, you're still talking about a significant amount of time and veterinary treatment that has to be administered either by the veterinarian or by adequately trained staff on the farm around the clock. This can result in fatigue and burnout of caretakers, too.
If a foal has to go to the veterinary clinic – for example, if it's colicking and it needs to be prevented from nursing to rest the gut – then you're looking at thousands of dollars for a bill on top of all that you've already invested to get that foal to this stage.
In Kentucky, we have not seen a noticeable uptick in deaths attributable to rotavirus, but it is very difficult to capture the full picture because a foal might not have been euthanized due to rotavirus, but perhaps a septic joint led to its demise, and we are concerned that those two things could be related, but don’t have sufficient data to call it. Without intensive and aggressive veterinary treatment young foals will absolutely die of rotavirus associated disease.
We don’t know if rotavirus infection has any long lasting effects on the gut. We know these foals can grow up to be superstars, as we have followed them out into their careers. However, the horse’s gut is closely tied to its immune system and overall wellbeing for the rest of its life, so this is an important, yet unanswered question.
What we know for sure is if you don't jump on this really quickly, young foals can certainly die of dehydration, acid-base imbalances, and electrolyte derangements.
In humans, rotavirus is still the biggest killer of children under five years of age in the developing world. This group of viruses is a big deal.
How To Prevent Rotavirus in Foals
Be very hands-off, be very diligent, always wear gloves when you're handling foals, always be very conscious, particularly when you're catching foals. Assign one of your hands as going to the dirty end (or the foal’s bum) and one hand for the clean end (or the foal’s mouth). I always put on double gloves so that if I have to ‘switch ends’ with my hands I can peel off a pair of gloves and still have a clean hand for the front end rather than a dirty glove. Practice excellent hygiene and remember that biosecurity can be enhanced by just not touching foals, which is really hard for people to do.
In our group, we are working on the Rotavirus B vaccine now. After extensive testing we are moving forward with one vaccine and are in the middle of a large clinical trial with hundreds of mares, so that we can understand whether this vaccine can perform well in the field. We certainly anticipate that it will, and we hope that this could make neonatal Rotavirus B a thing of the past in foals born in appropriately vaccinated mares.
No vaccine is perfect, unfortunately. But even if this vaccine could push the rotavirus infection off by several days, that would make a massive difference. If a foal gets sick on day 1 of its life, it is such a challenge, but if it gets sick on day 4 of life, it is generally not quite as difficult to manage.
We forget how quickly foals change in terms of how robust they are from day 1 to day 2 to day 3 of age. That doesn't mean to say that you're not going to get a really, really sick foal if it's affected at day 4, but we know that the intensity of treatment can be markedly reduced, typically speaking.
Closing Words
Number one is hygiene and contact with foals if you have an issue. Don’t struggle alone - call your veterinarian. I would certainly tell any of the farms, farm managers and breeders, that one of the most important things to do is not assume that you know what the cause of foal diarrhea or illness is. If your foal shows symptoms, take a sample, handle it appropriately, and send it off for appropriate testing.
Ensure that the lab you send it to can test for both Rotavirus A AND Rotavirus B in addition to the usual panel of disease associated organisms. It is vitally important that people don't just assume they know what the cause of the illness is. Spend the money to diagnose the problem, so that the foals can be treated effectively and efficiently.
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