Suspected chlorfenapyr poisoning in a horse.
Authors: Simões B P, Cerri F M, Takahira R K, Borges A S, Oliveira-Filho J P, Amorim R M
Journal: Journal of equine veterinary science
Summary
# Chlorfenapyr Poisoning in Horses: A Case Report Chlorfenapyr, a mitochondrial disruptor pesticide commonly used for caterpillar control, has well-documented toxic effects in humans and dogs but remains poorly characterised in equine medicine. This case report documents a 4-year-old Quarter Horse mare presenting with acute-onset excessive sweating, hyperthermia (elevated body temperature), tachypnoea, muscle fasciculation, and behavioural changes—clinical signs that developed within 24 hours of paddock spraying with chlorfenapyr. Serum biochemistry revealed abnormalities in renal and hepatic profiles consistent with mitochondrial toxicity, though the mare responded favourably to aggressive supportive care comprising intravenous fluid therapy, antipyretic and analgesic management with sodium dipyrone (25 mg/kg four times daily), and active cooling measures, ultimately achieving clinical recovery and discharge. The case highlights that equine practitioners should consider pesticide exposure in differential diagnoses when encountering horses with sudden-onset neurological, thermoregulatory, or muscular dysfunction, particularly in grazing animals following paddock treatments. Given the severity of potential chlorfenapyr toxicity and the lack of specific antidotes, prevention through careful pesticide application protocols and owner awareness remains paramount, alongside early recognition that intensive supportive care can facilitate recovery even when systemic organ involvement is evident.
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Practical Takeaways
- •Be alert to acute onset of hyperthermia, excessive sweating, respiratory distress, and muscle tremors in horses within 24 hours of pesticide application to grazing areas—chlorfenapyr poisoning may not be immediately suspected.
- •Implement supportive care (aggressive cooling, IV fluids, and analgesics) as primary treatment while awaiting laboratory confirmation; this case suggests horses may recover without specific antidotes.
- •Advise clients to keep horses away from paddocks during and for a reasonable period after pesticide spraying, and maintain documentation of products used for rapid diagnosis if clinical signs develop.
Key Findings
- •A 4-year-old Quarter Horse mare developed signs of chlorfenapyr poisoning (excessive sweating, hyperthermia, tachypnea, muscle fasciculation) within one day of paddock pesticide application.
- •Initial serum biochemistry showed abnormalities in renal and liver profiles consistent with chlorfenapyr's mitochondrial toxicity.
- •Horse responded positively to supportive treatment including intravenous fluid therapy, sodium dipyrone (25 mg/kg QID), and cold-water showers.
- •Patient was discharged without complications, demonstrating that early recognition and aggressive supportive care may be effective for chlorfenapyr intoxication in horses.