Felipe Reggeti, Nick Schrier, Marina Brash, Daniel Venne, Isabelle St-Pierre
Animal Health Laboratory, University of Guelph, Guelph, ON (Reggeti, Schrier, Brash); Scott Hatchery (Venne); Laboratoire de santé animale - MAPAQ (St-Pierre)
AHL Newsletter, 2020;24(2):14.
High mortality was observed in a barn housing 4-day-old broiler chickens over the first 48 hours of placement. Approximately 27,000 birds were at risk, but deaths were localized to the first 20 feet of the barn. Affected chicks were in ventral recumbency, appeared somnolent with closed eyes and had neurological signs consistent with leg paralysis (Fig. 1).
The barn had been sprayed with the pesticide Credo ® SC (Bayer) to help control darkling beetles; however, due to a presumptive mixing error, excessive amounts of concentrated product were applied to the walls near the barn’s entrance. This spray had dried out, leaving a white precipitate on the walls close to the floor (Fig. 2), and it was thought that the chicks had eaten this precipitate. The rest of the barn walls were sprayed with the remaining diluted solution, which did not leave the coating of white precipitate. When the flock veterinarian limited access to the walls using pieces of cardboard, the affected birds showed rapid clinical improvement.
Live chicks without contact to the white precipitate for 12 hours were submitted to the MAPAQ diagnostic laboratory in Québec city the next morning, but the birds appeared to be normal upon arrival, and there were no significant macroscopic or microscopic lesions on postmortem examination.
Liver samples were sent to the Animal Health Laboratory (AHL) for pesticide screening (pestscr). The samples were analyzed by liquid chromatography/electrospray ionization-tandem mass spectrometry, revealing a small peak consistent with trace amounts of imidacloprid (the active ingredient of the pesticide), confirming exposure. This finding, along with clinical presentation and exclusion of infectious diseases, supported a diagnosis of imidacloprid toxicosis. Rapid improvement of clinical signs after restricting contact to the white precipitate suggests fast metabolism of the toxic compound; therefore, submitting birds with clinical signs may increase the probability of identifying the toxin. Liver is the best sample, however, crop/gizzard contents may also be informative.
Imidacloprid is a group 4 neonicotinoid insecticide registered in Canada for applications including control of lesser mealworm (the darkling beetle Alphitobius diaperinus) larvae and adults in poultry facilities (1). Neonicotinoid pesticides were derived from modifications of nicotine, a plant alkaloid with insecticidal properties extracted from tobacco leaves. Similar to nicotine, the pharmacological and toxic effects of these new compounds involve activation of nicotinic acetylcholine receptors; however, while these effects are exerted in the central nervous system of insects, they are mostly restricted to the peripheral nervous system in vertebrates due to their low lipophilicity and poor penetration of the blood-brain barrier (2). Because of this relative selectivity, neonicotinoids are generally considered to be less harmful to vertebrates, explaining the popularity of these pesticides. However, some neonicotinoids, including imidacloprid, are particularly toxic to birds. Multiple cases of toxicity in game and wild birds have been recorded from ingestion of insecticide-coated seeds (3). In the poultry industry however, exposure is more likely to occur from ingestion of poisoned beetles or direct exposure to the substance, as reported in this case. Clinicopathological findings in experimental imidacloprid toxicity studies in broiler chickens have been reported elsewhere (4). AHL
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| Figure 1. Affected bird in ventral recumbency, with splayed right leg and closed eyes (4). | Figure 2. White “chalky” precipitate at the bottom of walls near barn entrance (courtesy of Dr. Venne) |
References
1. Health Canada. Consumer Product Safety Pesticide Label Search. 2019 August 28. Accessed 2020 May: https://pr-rp.hc- [1]sc.gc.ca/ls-re/index-eng.php [1].
2. Costa LG. Toxic effect of pesticides. In: Casarett & Doull's Toxicology: The Basic Science of Poisons, 8th ed. Klaassen CD,
ed. McGraw-Hill, 2013:955.
3. Millot F et al. Field evidence of bird poisonings by imidacloprid-treated seeds: A review of incidents reported by the French
SAGIR network from 1995-2014. Environ Sci Pollut Res Int [2] 2017;24(6):5469–5485.
4. Komal RP et al. Clinico-pathological studies of imidacloprid toxicity in broiler chickens. Haryana Vet 2016;55(2):163-165.