D O U B L E T H R E AT S
• Vaccinate. The vaccine against PHF is recommended by the American Association of Equine Practitioners (AAEP) for horses likely to be exposed to the disease. “The vaccine is typically administered twice yearly, in spring pring and fall, but this schedule varies geographieographically and is dependent upon recommenecommendations of the veterinarian,” saysys Gilsenan. “In regions with a long hot season, it might be appropriate to vaccinate more frequently.”
• Reduce exposure to species that carry Turn off barn and outdoor lights that may attract mayflies and caddisflies, which are known to fly for miles to swarm under streetlights and other light sources. Research shows that horses stabled at the ends of aisles, near open doors and night-lights, are at a much higher risk of contracting PHF.
“There was one report of a show barn that was having problems with PHF even though it was miles from a river,” says Grenager. “They had a lot of big safety lights on at night and a number of the horses got PHF. After they turned off the lights at night, the PHF cases dropped off significantly. Many people like to have a security light left on at the barn, but you have to weigh in the risks for PHF.” If security is a concern, consider installing motion detectors on your exterior barn lights, so they will come on only when someone is present.
• Store hay indoors or under a cover.
• Keep horses at some distance from water sources. If your pastures contain natural ponds or streams, consider fencing them off; horses grazing too close to the water’s edge may pick
Two pathogens found in water may do more harm to you than to your horse: cryptosporidium and giardia.
Cryptosporidiosis, which is seen mainly in calves, lambs, foals and other young animals, is an intestinal disease caused by Cryptosporidium spp. protozoans, especially C. parvum. “It’s generally not an adult disease unless it’s an individual with a compromised immune system,” says Michelle Abraham Linton, BSc, BVMS, DACVIM (LAIM), of the University of Pennsylvania. “Theoretically, older horses or those with unregulated Cushing’s could be at risk, or a horse that has been on chemotherapy.”
This pathogen, which causes severe diarrhea, is passed out with the feces, meaning that hygiene is a primary concern. “Crypto is highly infective,” Linton says. “You don’t have to ingest very much of the pathogen to have a serious problem.”
Crypto can infect many species of animals, and mature horses may carry the parasites and pass them on without showing signs of illness. “Many horses have been exposed to crypto. One study looking at blood tests showed that about 90 percent of the horses sampled had antibodies to C. parvum,” says Nora Grenager, VMD, of Grenager Equine Consulting. “This means it is in their environment, but when the researchers in another study took fecal samples from normal horses only about 8 percent of them were shedding it.”
Giardiasis is another disease caused by a protozoan, Giardia spp., that people can get by drinking water contaminated by wildlife feces. As with crypto, the cysts shed by giardia organisms can persist for many months in wet environments.
Horses don’t get sick from giardia, but they may carry the parasite and shed the cysts in their manure. “This disease is present in the environment, and horses are potentially shedding giardia, but it doesn’t seem to be associated with diarrhea very often,” says Grenager. “There have been studies and tests trying to determine the prevalence in horses, and how often normal horses have giardia cysts in their feces. Recent studies showed 10 to 20 percent of foals in some European countries were positive when checking feces.”
scanning electron micrograph of a trophozoite, the free-swimming form of the protozoan T The protozoan parasite cr the parasitic infection cryptosporidiosis.