The effect of cattle-administered ivermectin and fipronil on the mortality and fecundity of Anopheles arabiensis Patton

Abstract

BACKGROUND: Malaria control primarily depends on two vector control strategies: indoor residual spraying (IRS) and long-lasting insecticide-treated nets (LLINs). Both IRS and LLIN target indoor-biting mosquitoes. However, some of the most important malaria vectors have developed resistance against the chemical compounds used in IRS and LLINs. Insecticide-induced behavioural changes in vectors, such as increased outdoor feeding on cattle and other animals, also limit the efectiveness of these strategies. Novel vector control strategies must therefore be found to complement IRS and LLINs. A promising tool is the use of cattle-applied endectocides. Endectocides are broad-spectrum systemic drugs that are efective against a range of internal nematodes parasites and blood-feeding arthropods. The aim of this study was to investigate the efect of two endectocide drugs, injectable ivermectin and topical fpronil, on the survival and fecundity of zoophilic Anopheles arabiensis. METHODS: Laboratory-reared mosquitoes were allowed to feed on cattle treated with either injectable ivermectin (0.2 mg/kg), topical fpronil (1.0 mg/kg) or saline (control) on days 0, 1, 4, 7, 13, 21 and 25 post-treatment, and mortality and egg production were recorded daily. RESULTS: Compared to controls, the mortality of An. arabiensis increased by 3.52- and 2.43-fold with injectable ivermectin and topical fpronil, respectively. The overall fecundity of mosquitoes that fed on both ivermectin- and fproniltreated cattle was signifcantly reduced by up to 90 and 60%, respectively, compared to the control group. The efects of both drugs attenuated over a period of 3 weeks. Injectable ivermectin was more efective than topical fpronil and increased mosquito mortality by a risk factor of 1.51 higher than fpronil. Similarly, both drugs signifcantly reduced the fecundity of An. arabiensis. CONCLUSIONS: This study demonstrates that injectable ivermectin and topical fpronil are able to suppress An. arabiensis density and could help to reduce outdoor malaria transmission. Data from the present study as well as from other similar studies suggest that current-generation endectocides have a limited duration of action and are expensive. However, new-generation, sustained-release formulations of ivermectin have a multi-week, high mortality impact on vector populations, thus holding promise of an efective reduction of outdoor malaria transmission.