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Department of Family Medicine

Fire Ants

BACKGROUND

  • There are two species of imported fire ants (IFA): the black ant, Solenopsis richteri, and the red ant, Solenopsis invicta. Both are native to South America (Uruguay and Brazil respectively). They are believed to have been brought into the U.S. through Mobile, Alabama between 1918 and 1935 in infested nursery stock or in soil used for ship ballast.
  • Both ants are about a quarter inch in length. The red ant is reddish brown in color and the black ant is brownish black. The ants are easily identified by their characteristic mounds which may be several inches to a couple of feet high.
  • Over 250 million acres, primarily in the Sun Belt States, have become infested.
  • The IFA sting is a two-step process. First the IFA attaches itself to the skin with its jaws. With a firm grip, the ant inserts its stinger (located at the tip of the abdomen) into the skin. Venom is released from the poison sac again and again as the ant pivots inflicting multiple stings. The stinger is permanent and is not lost as with bees.
  • IFA venom is unique in the animal kingdom with a low protein content (1%) and a high piperidine content (99%). The piperidine is responsible for the burning sensation of the wound. The venom is hemolytic, bactericidal, and insecticidal. Unlike bee venom, which is high in protein, a non-allergic adult can sustain dozens of IFA stings with little systemic toxicity.

THREE MAJOR EFFECTS OF IFA STINGS:

1. Localized Irritation

80% of victims develop a local, non-allergic response to the IFA venom. In 8 to 24 hours, a characteristic small, blister-like vesicle forms which turns into a sterile pustule. The polysaccharide venom (99% piperidine) stings like pepper and attracts white blood cells to the site. The pustules rupture and scar in 3 to 7 days.

  • Secondary infection may occur if the pustule is scratched or broken. Diabetics and others with circulatory disorders, including varicose veins and phlebitis, are at special risk for complications.
  • Pustules require only ice or cold compresses, rest, and elevation of the extremity.
  • An over-the-counter topical antihistamine lotion may help relieve itching and burning.
  • Clean the vesicles with soap and water to prevent secondary infection.
  • Do not break the pustule. If infection is suspected, seek medical attention.

2. Exaggerated Local Response

15% of victims develop an exaggerated local response which is characterized by allergic swelling at the site of the IFA sting. It can be caused by a single sting. Swelling may last for several days and may be accompanied by itching, redness, and pain. Since the swelling is due to allergy, not infection, antibiotics are not necessary. Patients in this category characteristically do not progress to the more severe allergic response - anaphylactic shock.

  • Ice or cold compresses, rest, and elevation of the extremity to reduce swelling and pain.
  • An over-the-counter topical antihistamine lotion may help relieve the itching, burning, and swelling.
  • If symptoms persist, seek medical attention. Your physician may decide to prescribe an antihistamine and a trial of oral steroids.

3. Anaphylactic Shock

1-2% of victims develop generalized anaphylactic shock which is a life threatening, allergic reaction. This may occur within minutes of the sting and can occur the first or second time a person is stung. Adults are more susceptible than most children. Symptoms include swelling of the throat, face, eyes, unconsciousness, and difficulty in breathing.

If there is a Medical Emergency, Call 911

  • Anaphylaxis is a medical emergency requiring immediate medical attention. Telephone for an ambulance or transport the victim to the nearest medical care facility.
  • Anyone who develops hives or swelling away from the site of the sting is at risk and should report immediately to a physician!
  • Anaphylaxis victims require:

1. Diagnosis

2. Prescription of two epinephrine self-injectors (Epi-Pen © ) for self administration (one may not be sufficient for a severe anaphylactic reaction)

3. Prompt referral to an allergist who will confirm the diagnosis and start the patient on a course of desensitization.


 
 
 

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