Even when horses look like they're simply grazing peacefully in their paddocks, their bodies are on full defense. | Photo: iStock

If your horse survives one of these 5 infections, he might still suffer lasting effects.

Every day a passel of pathogens pokes and prods at your horse’s immune system, trying to find a breach in the barrier. Even when horses look like they’re simply grazing peacefully in their paddocks, their bodies are on full defense. On a daily basis, for instance, they might encounter:

• Soil-borne bacteria such as Rhodococcus equi in foals;
• Bacteria such as Leptospira (which causes leptospirosis), which live in pasture puddles, ponds, and streams;
• Mosquito-borne viruses such as West Nile virus and Eastern equine ­encephalitis;
• Other insect-borne bacteria, such as those that cause Lyme, piroplasmosis, and anaplasmosis from ticks;
• Bacteria or viruses from herdmates or horses coming and going from equine facilities, including herpesviruses, equine influenza virus, coronavirus, Salmonella, and Streptococcus equi subspecies equi (strangles); and
• Parasites such as tapeworms and the causative agents of equine protozoal myeloencephalitis (EPM).
• And as if the pathogens weren’t enough of a threat, there’s also the toxins some can produce—and might be found in forage—that can cause diseases such as botulism.

Your horse often can’t avoid these merciless microbes, which makes an optimally functioning immune system imperative. Luckily, most horses have fully functional immune systems; they just need a boost from time to time, in the form of vaccination, or help from antibiotics or from supportive care such as intravenous fluids, anti-inflammatory drugs, etc. After simple, straightforward infections such as rainrot or run-of-the-mill upper respiratory tract issues, most horses fully recover. In other cases patients potentially suffer long-term effects that negatively impact their performance and quality of life.

In this article we’ll learn which diseases most commonly cause post-infection illnesses, why some linger far past their welcome, and how they can impact long-term health, use, and quality of life