Possible Eprinomectin toxicity in a calf
Travis May, MS, PhD
A two-month-old, 150-pound, Brahman-cross heifer calf was observed with neurologic signs following application of what was believed to be a permethrin-based insecticide. The calf died following symptomatic treatment. Fresh and fixed tissue samples were submitted to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) for testing. A portion of fresh brain was extracted and analyzed using liquid chromatography – tandem mass spectrometry (LC-MS/MS) for the presence of permethrin and avermectin insecticides. Eprinomectin was detected in the brain by LC-MS/MS at a concentration of 658 parts per billion (ppb). No other chemicals were detected.
Eprinomectin is a broad-spectrum avermectin topical endectocide that is approved for use in beef and dairy cattle in the United States and over fifty countries worldwide. Compounds in the macrocyclic lactone class act as an agonist of the GABA (gamma-aminobutyric acid) neurotransmitter in nerve cells and selectively bind to glutamate-gated chloride ion channels in the nerve and muscle cells of the parasite. Generally, cattle tolerate treatment with eprinomectin very well. Presence of eprinomectin in brain tissue indicates it crossed the blood-brain barrier, which may occur at very high doses or if the blood-brain barrier is compromised in some way. Microscopic examination of fixed brain tissue from the calf did not reveal lesions indicating the blood-brain barrier had been compromised.
To learn more about this case, contact. Dr. Travis Mays, Analytical Chemistry Section Head at the College Station laboratory. For more information about TVMDL’s test offerings, call 1.888.646.5623 or visit tvmdl.tamu.edu.