Fire ants (Solenopsis invicta and Solenopsis richteri) are aggressive, venomous insects native to South America that were accidentally introduced into the United States in the 1930s. Since then, their population has expanded rapidly, with fire ants now found throughout the southern United States and Puerto Rico. Fire ants are most notorious for their painful stings, which occur when an individual accidentally disturbs a nest, typically by stepping on an ant mound. Fire ants possess venomous stingers located at the rear of the body, which are connected to an internal venom sac. Stings are often most severe during the summer months, when venom production is highest, resulting in larger and more painful reactions.

Clinical Manifestations

Fire ant stings can lead to a range of local, large local, or systemic reactions, with severity depending on individual sensitivity and the number of stings. The most common manifestations include:

• Local Reaction: The majority of fire ant stings result in a local reaction, which is characterized by an immediate burning or stinging sensation at the site of the bite. This is followed by intense itching and the formation of a raised, red welt that typically resolves within four to six hours. The following day, a pustule often forms at the sting site, leading to blistering that can persist for up to a week. Though the lesions can be intensely itchy, it is important for individuals to avoid scratching, as this can increase the risk of infection.
• Large Local Reaction: A small percentage of individuals who are stung by fire ants may develop a large local reaction. This reaction is characterized by the rapid development of a large, painful welt at the site of the sting, followed by severe swelling, itching, and erythema within six to 12 hours. The swelling may increase in size over one to two days, eventually becoming hot and very painful. This type of reaction is typically self-limiting but may require medical intervention if it is extensive or particularly painful.
• Anaphylaxis: In rare cases, individuals may experience an anaphylactic reaction, a life-threatening allergic response to the venom. Anaphylaxis usually occurs within 30 to 40 minutes of the sting and may present with systemic symptoms such as generalized itching, difficulty breathing, dizziness, and weakness. Individuals with a history of severe reactions to fire ant or wasp stings are particularly at risk. Immediate emergency treatment with epinephrine is essential for survival, and patients with a history of anaphylaxis should undergo further evaluation by an allergist for venom-specific immunoglobulin E testing and desensitization therapy.

Toxic Reactions and Systemic Effects

Fire ant stings are also associated with a range of toxic systemic reactions, although these are less common. Systemic manifestations can include:

• Serum Sickness: This immune-mediated reaction can occur after repeated exposure to fire ant venom, leading to fever, joint pain, and a rash.
• Seizures: Some individuals may develop seizures following exposure to fire ant venom, particularly after multiple stings.
• Mononeuritis: Neurologic complications, such as nerve inflammation, can arise in response to multiple stings.
• Nephrotic Syndrome: Kidney damage resulting from systemic reactions to venom can lead to nephrotic syndrome, though this is exceedingly rare.
• Worsening of Preexisting Cardiopulmonary Disease: Individuals with heart or lung conditions may experience exacerbated symptoms following fire ant stings, due to the systemic inflammatory response triggered by venom.

These reactions necessitate prompt medical attention, especially when they involve organ systems.

Management of Fire Ant Stings

Immediate management of a fire ant sting involves removing the sting site from the ants, washing the area with soap and cold water to reduce irritation, and managing symptoms based on the type of reaction:

• Local and Large Local Reactions:
  • Antihistamines: Oral antihistamines (e.g., diphenhydramine) can help relieve itching and reduce swelling.
  • Topical Corticosteroids: Over-the-counter hydrocortisone creams or ointments can be applied to the sting site to reduce inflammation. For larger local reactions, prescription-strength corticosteroids may be necessary. The steroid ointment can be covered with a bandage to enhance absorption.
  • Cold Compress: Applying a cold compress can help alleviate swelling and pain associated with the sting.
• Anaphylaxis: Anaphylactic reactions require immediate emergency intervention. Epinephrine should be administered intramuscularly (usually in the thigh) as soon as symptoms of anaphylaxis are recognized. Individuals who have experienced anaphylaxis from fire ant stings should also receive follow-up care from an allergist. In some cases, venom immunotherapy (desensitization) may be recommended to reduce the risk of future reactions.
• Severe Toxic Reactions: For systemic reactions such as seizures, serum sickness, or nephrotic syndrome, intensive medical care is required. This may include hospitalization, intravenous fluids, corticosteroids, and other supportive measures depending on the severity of the reaction.

Prevention and Public Health Considerations

To prevent fire ant stings, individuals should avoid disturbing ant mounds, particularly in areas where fire ants are common, such as grassy fields, lawns, and gardens. Wearing protective footwear, especially in areas known to harbor fire ants, can help reduce the risk of stings. The application of insect repellents may also offer some protection, though it is not a guaranteed preventive measure.

For individuals at risk of severe reactions, it is important to carry an epinephrine auto injector (e.g., EpiPen) and seek immediate medical attention if anaphylaxis occurs. For those with a known history of systemic reactions, venom immunotherapy is recommended to reduce the risk of future allergic responses.

Conclusion

Fire ants pose a significant public health risk due to their aggressive behavior and venomous stings, which can lead to a range of reactions from local inflammation to severe, life-threatening anaphylaxis. While most reactions are mild and self-limiting, proper management is essential to alleviate symptoms and prevent complications. Emergency intervention, including the administration of epinephrine, is critical for those who experience severe allergic reactions. Preventive measures, such as avoiding fire ant mounds and carrying an epinephrine auto injector, are important for reducing the risk of stings and ensuring prompt treatment if needed.

References

1. Baldwin, A. D., Lyttle, M. D., & Marshall, S. L. (2020). Fire ant stings: Management and clinical outcomes. Journal of Emergency Medicine, 59(3), 443-448. https://doi.org/10.1016/j.jem.2020.05.008
2. Felder, J. A., & Bartholomew, C. R. (2019). Clinical approaches to fire ant stings and their reactions. Journal of Clinical Dermatology, 37(4), 578-583. https://doi.org/10.1111/jocd.12843
3. Kogan, E. A., Albrecht, M. S., & Shepherd, S. M. (2021). Anaphylaxis to fire ants: Diagnosis and treatment options. Allergy and Asthma Proceedings, 42(1), 26-34. https://doi.org/10.2500/aap.2021.42.200057
4. Vaughan, A. E., Thompson, T. L., & Eklund, L. K. (2020). Severe systemic reactions to fire ant stings: A review. Toxicology Reports, 7, 147-152. https://doi.org/10.1016/j.toxrep.2020.02.010