All About Fire Ant Allergy

What are fire ants and where are they found? What types of reactions may occur after a sting? How is a fire ant allergy diagnosed and what are the options for treatment? These are very important questions as more than half of the people who live in areas where fire ants are found receive stings each year. Of those people who are stung, in turn, around half have some type of allergic reaction. Even without an allergic reaction, however, fire ant stings can lead to discomfort and the risk of infection.

What Are Fire Ants?

The imported fire ant (IFA) is a type of stinging ant that was accidentally imported into the United States from South America in the early 1900s. Since their introduction into the port of Mobile, Alabama, IFAs have spread into much of the southeastern United States and Texas. IFAs also colonize limited areas of Arizona and California. While there are native species of fire ants present in the United States, they do not pose the same threat to humans as the IFA.

How Common Are Stings?

Since IFAs are so common in the southeastern United States, people are frequently stung by them. The chance of being stung is greater than 50% over the course of a year for the general population; the rate is probably much higher for those with outdoor hobbies and occupations, such as outdoor sports and gardening.

IFAs have also been reported to sting people indoors, including in nursing homes, private homes, and hotels. In fact, it's thought that the elderly and those with disabilities may be at even greater risk of stings from the pesky creatures.

When fire ants encounter humans, they tend to sting. People are usually stung multiple times and by multiple ants. An IFA actually grasps a person’s skin with its jaw and tucks its hind end under in order to sting. The ant will then remove its stinger, rotate in a circular fashion, and sting again.

The combination of large numbers of fire ants in a nest and the ability to sting repeatedly leads to multiple stings for many people. In fact, up to 10,000 fire ant stings have been reported for a single person.

Fire ants are small and typically red or black in color. They live in large colonies in the ground and typically build mounds. Fire ants are related to other flying stinging insects such as honeybees, wasps, and hornets.

Allergic Reactions

There are several types of reactions that can occur in response to a fire ant sting.

Usual Reactions

Usual (typical) reactions occur in essentially 100% of people stung by IFAs and include localized pain, swelling, and redness at the site of the sting. Within 24 hours, a pus-filled blister will develop at the site of the sting. This blister is not infected; it is caused by a component of the fire ant venom. A usual reaction is not a sign of an allergy, but rather a physical response to the sting.

Large Local Reactions

Large but localized reactions are probably allergic in nature and occur in up to 50% of people who are stung by an IFA. Symptoms include a large area of swelling, redness, pain, and itching at the site of the sting, and occur within 12 to 24 hours of being stung.

Anaphylaxis

A whole-body allergic reaction, also known as anaphylaxis, occurs in roughly 1% of people who are stung by IFAs. Considering how common fire ant stings are in regions where these insects live, this is a significant problem. An anaphylactic reaction can be severe and even life-threatening.

Symptoms of anaphylaxis from IFA stings may include any of the following:

• Itching all over
• Hives or swelling that spreads from the site of the sting
• Flushing
• A runny nose, sneezing or postnasal drip
• Itchy/watery eyes
• Swelling of the lips, tongue or throat
• Shortness of breath, wheezing or coughing
• Stomach cramping, nausea, vomiting or diarrhea
• Lightheadedness, fast heart rate, low blood pressure or passing out
• Sense of panic or a sense of impending doom
• Metallic taste in the mouth

Toxic Reactions

Toxic reactions can mimic anaphylaxis but are due to a very large number of stings – typically in the hundreds. In a toxic reaction, however, there is no allergic antibody present; symptoms are caused by the large amount of venom that is injected.

Diagnosing Fire Ant Allergy

Typically, the diagnosis of allergy to IFAs is made with a history of an allergic reaction to a fire ant sting, along with a positive allergy test. Skin testing using IFA extract is the preferred method of allergy testing; blood tests, such as a RAST, are reasonable alternatives to skin testing.

The diagnosis of allergy to fire ants should only be performed in those people who should be considered for allergy shots, or immunotherapy, using IFA extract.

Testing is not needed: If a person has never been stung by IFA or never had any symptoms (other than usual reactions) as a result of a sting, there is no need to perform any venom allergy testing.

If a child under 16 years of age only experiences skin symptoms (such as hives and swelling) after a sting, there's no need for allergy testing. This is because anaphylaxis will only occur in up to 10% of future insect stings. However, if there is significant concern about the small chance of anaphylaxis with future stings in this group, testing, and treatment for IFA allergy is reasonable.

If a child or adult has a large local reaction in which swelling occurs at the site of the sting only, this is not usually a reason to perform venom testing or to administer IFA allergy shots. This is because the chance of developing anaphylaxis with future stings is only about 5 to 10% for both children and adults. (A few studies show that these reactions can be decreased with the use of IFA immunotherapy, and this may be required in situations where stings are frequent and the swelling disrupts a person’s quality of life or ability to work.)

Testing is needed: If a person of any age has symptoms of anaphylaxis after being stung, testing should be done. That's because the person has about a 50 to 60% chance that future insect stings will cause a similar reaction . The chance of a reaction to a future sting will decrease over time, but it still remains at about 20% many years after the last sting.

Treatment

The treatment of fire ant stings and allergy depends on the degree of the reaction experienced in the past. Treatment includes not only management in the acute setting but chronic treatment (such as shots) and prevention (avoidance).

Avoidance

The best way to prevent an allergic reaction is to avoid being stung. Here are a few tips:

• Hire a trained exterminator to treat any known IFA mounds in the immediate area; periodic surveillance for further infestation should be performed.
• Fire ant bait, obtained at most hardware stores, can be sprinkled onto mounds or over large areas to prevent new infestations.
• Always wear shoes when walking outside, particularly on grass.
• Wear pants, long-sleeved shirts, gloves, close-toed shoes, and socks when working outdoors.

Treatment of Acute Reactions

Pustules: There is no known treatment to prevent the formation of pus-filled blisters (pustules). Once a pustule has formed, it should simply be kept clean and dry, and gently washed with soap and water. A pustule is not infected, but secondary infections from disrupting the pustule are very common. Pustules formed from IFA stings will heal within three to 4 days. Applying first aid creams such as Bacitracin or Neosporin, and keeping the area covered may decrease the chance of an infection.

Large local reactions: Large local reactions can be treated with over-the-counter anti-inflammatory medications, such as Advil (ibuprofen), as well as antihistamines, such as Claritin (loratadine) or Benadryl (diphenhydramine). Ice can be applied to the area, and the area can be elevated to decrease swelling. Lastly, a topical steroid, such as hydrocortisone 1% cream, can be applied to the local reaction site.

Anaphylaxis: The treatment of anaphylaxis from IFA stings is essentially the same as the treatment of whole-body reactions to other flying stinging insects such as bees. This includes the use of injectable epinephrine (an EpiPen).

Curative Therapy

Allergy shots, or immunotherapy, using IFA extract can cure fire ant allergy. This concept is essentially the same as shots for other flying stinging insect allergies, and the same principles apply as do for the treatment of bee sting allergy.

A Word From Verywell

Fire ant stings are common, affecting the majority of people who live in proximity to these insects each year. Of these people, roughly half will have some degree of fire ant allergy. Most of these will be large local reactions, and though unpleasant, specific treatment to cure the allergy is not usually needed.

For those who have anaphylactic reactions, however, curative therapy with allergy shots is one way to prevent these most serious of allergic reactions.

Regardless of the degree of fire ant allergy, however, understanding the symptoms of anaphylaxis, and being prepared with an EpiPen is a must.