The level of equine parasite transmission should be diminished on pastures that were so flooded they had to be evacuated, said Craig Reinemeyer, DVM, PhD, president of East Tennessee Clinical Research in Knoxville, Tenn. “Many larvae would get washed away, and others would go down into the soil,” he said. “In either case, climatic conditions right now along the Gulf Coast aren’t favorable for long-term survival of infective stages (the hotter it is, the quicker they die). So, horses going back to their original pastures may theoretically face less challenge than usual. Of course, there won’t be much forage to eat either, so their nutritional challenges will be more significant than the worms.”

Regrettably, Reinemeyer added, the infective stages on pasture aren’t going to drown.

He noted that heavy precipitation is known to break down manure piles and distribute infective larvae onto wider areas of pasture for eventual ingestion by grazing horses. “Of course, that takes place several times a year under normal climatic conditions, and only requires about 2 cm of water, not nine feet,” he stated. This would mean owners or caretakers would need to make sure horses are dewormed on schedule.

He also said because of the flooding there might be a small chance for other strains of parasites to be brought onto your property. “It’s possible that some parasites that were not native to your farm may come floating in from down the road,” said Reinemeyer. “These differences could be qualitative (i.e., different species; for instance, Strongylus vulgaris coming back if you’d previously eradicated it on your pastures) or quantitative (e.g., resistant strains of some worms might be brought in with the floodwaters, which would mean dewormers that previously were effective on your farm might not be in the future)