Unusual cause of seizures: Imported fire ant bite reaction

INTRODUCTION

Ant bites usually lack any serious sequelae. Neurological manifestations and complications there off are very rare. After an exhaustive literature search, we found anecdotal case reports of ant bite precipitating seizures. This is a similar case of ant bite of species Solenopsis leading to neurological manifestations.

CASE REPORT

A 56-year-old lady teacher, from interior Tamil Nadu, with no comorbidities was alright until 2 weeks back when she experienced a painful ant bite on her back. She had throat discomfort, burning sensation at the bite site; had loss of consciousness, bowel, and bladder incontinence. Her coworkers noticed generalized tonic clonic movements involving bilateral upper and lower limbs for 30 s, followed by confused behavior for 3 h.

She had similar history 5 years back, when she noticed a sting on her toe, developed angioedema and an episode of seizures. She was started on anti-epileptic which she discontinued due to allergic reactions- likely carbamazepine induced mild Steven Johnson’s syndrome. She was bitten by similar ant in five other occasions in the past 4 years, when she had local swelling, swelling of lips, choking sensation, and giddiness; all resolved within 3 h.

Her workplace has a large ground with many ants, insects. School children at the same premises would develop self-resolving skin lesions after ant bite, but not seizures.

Her clinical examination was unremarkable, bite site had no signs of inflammation. Her baseline laboratory investigations, magnetic resonance imaging brain, and electroencephalogram were normal.

Suspecting a possible ant bite-related complication, the attenders were asked about the description of the ant and to bring one for perusal.

The ant picture and the physical verification matched with the description of imported fire ant (IFA) species Solenopsis invicta [Figure 1a and b].^[1]

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Figure 1:

(a) The ant brought for physical verification, (b) Solenopsis invicta.

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The patient was reassured on the cause of her symptoms and advised to take adequate precautions. She was explained how to address an allergic reaction and report to medical facility.

DISCUSSION

IFA are usually found in South America, also in India. Two species – S. invicta and Solenopsis richteri are termed as IFA.

Studies on similar ant bites have described pustular, papulovesicular eruptions which develop and resolve in a week’s time.^[2] This was not noted in our patient.

IFA stings can cause unconsciousness, convulsions, blurred vision, neuropathies, and encephalopathies. The probable mechanisms for these could be immunological reaction or immediate hypersensitivity reaction.^[2] The toxin is a complex fluid having cytotoxic, neurotoxic, and hemolytic components predisposing to hypercoagulable states.^[2,3] Piperadines in the venom inhibit sodium potassium ATPase, decreasing end plate membrane sensitivity to acetylcholine causing post-synaptic blockade. Cerebral hypoxia due to anaphylactic shock could precipitate seizures. Direct convulsant effect of the venom has been studied in rodents.^[4]

CONCLUSION

Seizures precipitated by an ant bite are quite uncommon. We have only few case reports regarding fire ant bite related neurological complications. We need more studies on the composition of fire ant toxin and its implication on neurobiology.