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 (LLIN). 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 LLIN’s. Insecticides-induced behavioural changes in vectors, such as increased outdoor feeding on cattle and other animals also limit the effectiveness of these strategies. Novel vector control strategies must therefore be found to complement IRS and LLIN’s. A promising tool is the use of cattle-applied endectocides. Endectocides are broad-spectrum systemic drugs effective against a range of internal nematodes parasites and blood-feeding arthropods. The aim of this study was to investigate the effect of two endectocide drugs, ivermectin and fipronil, on the survival and fecundity of zoophilic Anopheles arabiensis. Methods Laboratory-reared mosquitoes were allowed to feed on cattle treated with either ivermectin (0.2 mg/kg), fipronil (1.0 mg/kg) or saline (Control) on day 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 3.52 and 2.43 times with ivermectin and fipronil, respectively. The overall fecundity of mosquitoes that fed on both ivermectin- and fipronil-treated cattle was significantly reduced by up to 90% and 60%, respectively, compared to the control group. The effects of both drugs attenuated over a period of 3 weeks. Ivermectin was more effective than fipronil and increased mosquito mortality by a risk factor of 1.51 higher than fipronil. Similarly, both drugs significantly reduced the fecundity of An. Arabiensis. Conclusions This study demonstrated that ivermectin and fipronil are able to suppress An. arabiensis density and could help to reduce outdoor malaria transmission. The data from the current study as well as other similar studies suggest that current-generation endectocides have limited-duration action and are expensive. However, new-generation sustained-release formulations of ivermectin have multi-week high mortality impact on vector populations, thus holding promise of effective reduction of outdoor malaria transmission.