Fire Ant Bites and Stings Can Cause Horse Health Issues

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"Fire ants deliver a simultaneous bite and sting that are very painful and give them their infamous name. The threat of fire ants to healthy, ambulatory adult animals is fairly minimal. However, fire ants can be a significant threat to recumbent animals and to newborns if they lie down or are born on or near an ant bed. Before any field procedure, an essential routine for veterinarians is surveying the planned work area for any fire ant beds," according to Bryan Waldridge, DVM, DACVIM, currently of Kentucky Equine Research, in an article in the University of Kentucky's Equine Disease Quarterly,

According to the USDA, two species of imported fire ants (IFA) were introduced into the United States from South America at the port of Mobile, Alabama. The black imported fire ant, Solenopsis richteri Forel, arrived sometime around 1918, and the red imported fire ant, Solenopsis invicta Buren, in the late 1930s. Both species probably came to the port in soil used as ballast in cargo ships. Today, imported fire ants infest more than 343 million acres in Alabama, Arkansas, California, Florida, Georgia, Louisiana, Mississippi, New Mexico, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia and Puerto Rico. Imported fire ants are a major public nuisance because of their ferocious sting and aggressive behavior, and they also damage several agricultural commodities.

The USDA's Animal Plant Health Inspection Service (APHIS) noted that it works to prevent further imported fire ant spread by enforcing the Federal Quarantine (7 CFR 301.81) and "cooperating with IFA-infested states to regulate articles, such as nursery stock and soil-moving equipment. Also, APHIS evaluates the efficacy of regulatory treatments for preventing imported fire ant spread by artificial means and revises regulations and procedures as necessary. APHIS works with states, industry and other Federal agencies to develop and test promising new insecticides and biological control agents."

In order to try to control and eradicate imported fire ants, APHIS, along with other federal and state agencies, implement an imported fire ant phorid fly (Pseudacteon spp.) rearing and release program. The first two species of this biocontrol agent, P. tricuspis and P. curvatus,were released between 2002-2009 and have become established in more than 50% of the imported fire ant quarantined area. In 2010 there were multiple releases of a third fly species, and production rearing of a fourth species has begun.

"Immediate clinical signs of fire ant bites include intense pain, pruritis (severe itching of the skin) and erythema (superficial reddening of the skin)," noted Waldridge. "Fire ant venom is composed mainly of piperidine alkaloids and is less than 1% proteinaceous. Stings usually develop into pustules within 12 to 24 hours due to local necrosis caused by the piperidine alkaloids. Sometimes only secondary lesions such as erythema and epidermal collarettes may be noticed; affected skin may feel thickened and corrugated."

Waldridge said that neonatal horses can be killed if attacked by the many ants inhabiting a mound, but adult animals are unlikely to die as a result of fire ant stings. "The overall severity of clinical signs and disease is likely due to the number of ant stings suffered."

Waldridge said he saw a weanling horse that developed severe laminitis as a complication of multiple fire ant stings with nearly one entire side of the horse's body affected, necessitating euthanasia. "Anaphylactoid reactions are rare without massive exposure to stings and occur in those animals hypersensitive to the protein portion of fire ant venom," noted Waldridge.

Treatment of fire ant stings is largely symptomatic, noted Waldridge. "The ants often remain attached, and mechanical removal or bathing is needed," he advised. "The main goal of treatment is to reduce pruritis and pain using topical or parenteral corticosteroids and nonsteroidal anti-inflammatory drugs. Antihistamines may also be of benefit. Affected animals should be observed for any possible secondary complications such as laminitis, respiratory difficulty, abortion, etc. Most will have a full recovery after several days of mild to moderate pruritis and dermatitis."

The USDA advises anyone buying hay from an area infested with imported fire ants be cautious as the ants can be carried in the hay. For more information visit this page.

For more information about fire ants in the United States, including updates to maps and locations of fire ant quarantine visit the USDA website.

To determine whether the USDA has detected fire ants in your zip code you can go here.