BEWARE BLUE-GREEN ALGAE

The role of stagnant water as habitat for mosquito populations is well known, as are West0 Nile encephalitis, eastern0 and western0 equine encephalomyelitis and other diseases that mosquitoes can transmit to horses. But there’s another less common but serious threat associated with still water: blue-green algae.

Despite the name, blue-green algae are actually a type of bacteria, known as cyanobacteria, that create energy via photosynthesis. They are normally present in small numbers in most natural waters. Under the right conditions, however—in warm, still waters with high levels of phosphorus or nitrogen from fertilizer runoff—blue-green algae multiply quickly and form thick, floating mats called “blooms” or “pond scum.”

Some species of cyanobacteria produce toxins that can make both people and horses ill. “There are several different species of algae and they produce different toxins,” says Michelle Abraham Linton, BSc, BVMS, DACVIM (LAIM), of the University of Pennsylvania. “One is a neurotoxin that affects the central nervous system; the horse develops neurological signs. The other is a hepatic toxin that creates liver disease. We notice the more apparent neurological problems such as tremors, excess salivation, ataxia0 or acute death. There isn’t much you can do for the horse once signs appear.”

Horses may ingest the toxin when they drink affected water. “Some people feel that this disease is underdiagnosed because of the severity–if you just find the horse dead, it may be hard to determine the cause,” says Linton. “The important thing is to be able to identify the algae and make sure you don’t have it in any of the water sources where your horse might drink, especially in warm weather.”