Dr. Nathan Slovis covers new technologies in accurately diagnosing the causes of infectious diarrhea in foals.
In more than half the cases with diarrhea in foals, veterinarians never identify the underlying cause.Twenty percent of foals will get some form of infectious diarrhea, Slovis said during his presentation at the 2020 American Association of Equine Practitioners’ Convention, held virtually. And because so many possible causes exist, veterinarians often find themselves treating symptoms without really knowing what they’re up against.
Yet, that scenario is changing., according to Nathan Slovis, DVM, Dipl. ACVIM, CHT, director of the McGee Center at Hagyard Equine Medical Institute, in Lexington, Kentucky. Developing technologies—and even the use of certified sniffer dogs that can identify Clostridium difficile in humans—are making it faster and easier to diagnose whether the culprit is viral, bacterial, protozoal, or something else.
Routinely treating foals with antibiotics has become controversial, Slovis acknowledged. Antibiotics are ineffective against viruses, and there’s growing concern about antibiotic-resistant bacteria, including multidrug resistant strains of salmonella. Genetically engineered “bacteria-eating” viruses known as bacteriophages hold future promise for treating some of these antibiotic-resistant infections, but more research is needed.
Antibiotics do change the gastrointestinal (GI) tract microbiome, leaving researchers to wonder whether they simply make diarrhea worse. Nonetheless, Slovis generally favors giving sick foals a broad-spectrum antibiotic even when he suspects and confirms rotavirus. “Neonates are different than adults,” he said. “Bacteremia (bacteria in the bloodstream) occurs in 50% of foal diarrhea cases.” Because endotoxins can be deadly, his strategy is to quell any primary or secondary bacterial infections before the foal’s body is overwhelmed.
Slovis also made a strong pitch for vaccinating pregnant mares against rotavirus and salmonella. A two-dose vaccine for Salmonella typhimurium and agona (conditional license in Kentucky) can be given to mares at nine and 10 months of gestation or to foals of unvaccinated mares during their first month of life. The rotavirus vaccine requires three doses administered at eight, nine, and 10 months of gestation.
Studies show the rotavirus vaccine:
- Reduces infection rates by 50%;
- Reduces the duration of diarrhea from seven days to less than two days; and
- Prevents virus shedding in mares and foals.
Unfortunately, the currently available rotavirus vaccine only protects from the G3 strain, not the G14 strain that’s becoming more common in Kentucky and elsewhere, Slovis said. He hopes a pharmaceutical company might be persuaded to work on a vaccine offering crossover protection between these two equine strains.
Rotavirus hits young foals hard and fast, with a one- to two-day incubation period. The virus invades the GI tract and impacts the production of lactase, which interferes with milk digestion, leading to diarrhea and painful bloating. Using PCR is the best way to diagnose it. Immunoassay tests can also be helpful, he noted, but they must be validated for horses, because human rotavirus antigen tests can provide false negatives in equines. Therapies include providing fluids, ulcer medication, pain relievers, and lactase to support digestion, reduce bloating, and calm the bowels.
Bacteria can also plague young foals, with C. difficile, C. perfringens, and Salmonella common culprits. Slovis warned that types A and C of C. perfringens are associated with fatal foal necrotizing enterocolitis (damage and death of cells in the small intestine and colon), so there’s no time to waste. By the time a positive culture comes back from the lab, it could be too late. Again, he said PCR is the new gold standard for identifying bacterial loads, possibly providing results within hours.
Hygiene is hugely important in preventing or reducing foal diarrhea outbreaks. If barns are potentially infected, he suggests foaling mares outdoors until all stall surfaces, tack, and equipment have been thoroughly disinfected. Foaling kits should contain only single-use items and equipment that can be sterilized between uses. Slovis also recommended using disposable udder wipes to cleanse the mare’s udder and hindquarters before her baby nurses. A bath before or after foaling might also be in order.
Not every case of foal diarrhea is preventable. But faster, more accurate diagnostics reduce guesswork regarding treatment, leading to better outcomes for babies.