Sub-acute rabbit toxicity test for agrochemicals containing abamectin (2%) and acetamiprid (3%) formulation illicitly used to control acaricide-resistant ticks

Abstract

The increased occurrence of tick acaricide resistance to conventional acaricides has compelled farmers to use agrochemicals containing abamectin (2%) and acetamiprid (3%) solely or in combination with acaricides to control ticks, a practice that has been reported to cause blindness in cattle. This research assessed the ocular toxicity caused by the application of the above agrochemicals. It involved an experimental study in which eight New Zealand rabbits were kept in cages and acclimatized for two weeks in the experimental animal house. The rabbits were allocated to four groups (n=2), one of which served as a control. Proparacaine hydrochloride anesthetic was administered to all the rabbits five minutes before the application of the chemicals. Rabbits in group X were exposed to 0.03mg/ml abamectin, 0.045mg/ml acetamiprid (Dudu-acelamectin®), group Y, a combination of 0.166mg/ml Amitraz (Norotraz®), 0.013mg/ml abamectin and 0.02mg/ml acetamiprid (Dudu-acelamectin®), and group Z, 0.25mg/ml Amitraz (Norotraz®). Group C, the control was given the diluent, (distilled water). The pH of the treatment solutions was measured before use on the rabbits. Administration of the chemical was done every three days at a dose of 0.1mls, directly dropped into the left eye for a period of 21 days. Meloxicam analgesic was administered subcutaneous, eight hours after the application of the test chemicals. Measurements for body weight were done daily. At the end of the experiment on day 21, the rabbits were humanely sacrificed. Gross pathology, tissue processing, and histopathology were done on the eyes and the kidney. One-way ANOVA was used to test for significant differences in mean weight, blood, hepatic, and renal indices at 95% Confidence Interval using STATA. The pH of the diluted test chemicals was 6.9, 6.9 and 6.5 for Dudu-acelamectin (X), a combination of Dudu-acelamectin and Amitraz (Y) and Amitraz (Z), respectively. The weights of the rabbits in all groups generally increased from day 1 to 21. No observable changes were seen in the eyes of the rabbits during the course and at the end of the study. Biochemical and hematological results showed that there were no significant changes attributed to the chemicals. On histopathology, the eyes and kidneys were found to be normal with no significant lesions. It can therefore be deduced that sub-acute exposure at the above concentration of the chemical causes no significant ocular toxicity. Hence, more research should be done to assess the actual ratios of the chemicals used by farmers and investigate the outcome in a chronic (longer) ocular toxicity test.