Fire Ants and Horses
Fire ant's 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.
Immediate clinical signs of ant bites include intense pain, pruritis, and erythema. Fire ant venom is composed mainly of piperidine alkaloids and is less than 1% proteinaceous. Stings usually develop into pustules within 12-24 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.
Neonates 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. The author has seen a weaning horse that developed severe laminitis as a complication of multiple fire ant stings with nearly one entire side of the 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.
Treatment of fire ant stings is largely symptomatic. The ants often remain attached, and mechanical removal or bathing is needed. The main goal of treatment is to reduce pruritis and pain using topical or parenteral corticosteroids and non-steroidal 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 prutitis and dermatitis.
Equine Disease Quarterly, April, 2008. Dr. Bryan Waldridge, Rood and Riddle Equine Hospital, Lexington, Kentucky.