Evaluation of acute oral and sub-acute dermal toxicity of tick burn spray in mice and rats
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Existence of multi-acaricide resistant ticks in the south-western cattle corridor of Uganda has created windows for introduction of plethora of illicit chemicals for tick control including Tick Burn Spray (TBS). The dilemma with TBS ranges from debatable labels on its bottle (70mg/ml chlorpy and 20g/ml cypermethrin), absence on NDA catalogue to its unknown safety to livestock and/ livestock products and humans. This study aimed at investigating the active ingredients of TBS, as well as determination of acute oral and sub-acute dermal toxicity of TBS in mice and rats. Chemical analysis using in-house Gas Chromatography-Mass Spectrometer (GC-MS) discovered presence of 45% w/v metrifonate in TBS. In acute toxicity, 24 young adult mice divided equally into five treatment groups were exposed orally to 1ml of ascending doses of TBS with the aid of gavage tube. The main toxidrome shown by all exposed mice groups were ataxia, gait and posture abnormalities, respiratory disorder, increased salivation, urination, defecation, lacrimation, piloerection, tremors, convulsions, and subsequently death. Probit analysis revealed oral LD50 of TBS in mice to be 9.35 mg/kg at a standard error (S.E) of 0.44 mg/kg with 95% confidence interval. For sub-acute toxicity, a group of 12 rats were dermally exposed to 4mls of 5.625mg/ml of TBS for 21 days at 5 days intervals. Histopathological investigations indicated hepatic vacuolar degeneration (80%), perivascular necrosis (60%), splenic hemosiderosis (70%), and thickening of alveolar septa in the lungs (100%). Hematological findings discovered significant (p-value=0.01) average increase in the red blood cell counts from 8015000/µL in control group to 8490000/µL in the treatment group. Liver function tests also showed significant average increases in the levels of alanine aminotransferase from 67.0 U/L to 158.5 U/L and, aspartate aminotransferase from 155.0 U/L to 272.0 U/L in treatment groups. The findings of kidney function test showed a p-value=0.01, average decreases in the plasma level of sodium ions from 140.5 to 128.5 mEq/L and chloride ions from 99.3 to 92.4 mEq/L in the treatment groups. In conclusion, the findings of this study indicates that the active substance (metrifonate) present in Tick Burn Spray is highly toxic to the liver, lungs and the spleen of the rats, and hence its usage may potentially be detrimental to the health of humans, livestock and environment. Therefore, national vigilance criteria and policy should be set for the public to restrict, identify, report and prohibit usage of illicit, smuggled, non-registered acaricides, or agrochemicals. Further trials should be conducted to ascertain the chronic toxicity of this product on livestock.