Repellent and larvicidal properties of selected indigenous plants in the control of Anopheles mosquitoes.

BACKGROUND OBJECTIVES: Widespread pyrethroid resistance and plastic-feeding behaviour of most malaria vectors across Africa threaten the efficacy of current insecticide-based vector control interventions like Insecticide-Treated Nets (ITNs) and Indoor Residual Spraying (IRS). This study examined the larvicidal activity ofMorinda citrifolia against Anopheles gambiae larvae and the repellent properties of Morinda citrifolia (Noni), Moringa oleifera (Moringa), and Ocimum basilicum (Basil) as complementary vector control tools against Anopheles gambiae sensu lato (s.l.). METHODS: Noni, Basil, and Moringa oil extracts were obtained with the extraction techniques; Soxhlet, steam distillation and maceration respectively, using hexane and ethanol. The effectiveness of the extracts was assessed using the WHO standard larval susceptibility bioassay and guidelines for repellent efficacy. Following bioassays, effective doses (ED) and lethal concentrations (LC) were determined. Gas Chromatography-Mass Spectroscopy analysis was performed to identify the bioactive chemical components of the extracts of Moringa oleifera and Ocimum basilicum. RESULTS: Emulsified Morinda citrifolia seed oil had LC50=68.3, LC90=130.9 and LC99.9=222.5, and ED99. 9=308.3%v/v, the ethanolic extract of Moringa oleifera leaves had ED99.9= 1.25g/ml, and essential oil of Ocimum basilicum leaves had ED99.9=0.28g/ml against Anopheles gambiae. INTERPRETATION CONCLUSION: The results obtained indicated that seed oil of Morinda citrifolia, essential oil of Ocimum basilicum, and crude extract of Moringa oleifera have repellent activity against An. gambiae s.l. The complete protection time (CPT) of Morinda citrifolia, Moringa oleifera, and Ocimum basilicum was 120 min, 72 min and 84 min at ED99.9 respectively. Morinda citrifolia oil exhibited larvicidal effects against the larvae of An. gambiae s.l. The results provide valuable information for the use of the plants as biocides.

Risk factors affecting the feeding site predilection of ticks on cattle in Ghana.

Ticks are important disease vectors affecting animal health and causing substantial economic loss, especially in the tropics and subtropics. To examine the tick burden of cattle and associated risk factors for tick infestation, ticks were collected from 388 cattle within five regions in Ghana. Most of the cattle were males (50.3%) and generally older than 3 years (65%). Of the animals sampled, 2187 ticks were collected with a mean tick burden of 5.6 ticks per cattle, and the average tick burden on the udder/scrotum being significantly higher than in the anal region (Generalized Linear Mix Model [GLMM], p = 0.01197). The tick species identified were predominantly Amblyomma variegatum (42.6%) and Hyalomma rufipes (26.2%). High proportions of cattle examined were found to have A. variegatum infesting the udder/scrotum. Furthermore, H. rufipes infested mostly the anal region compared to other examined body parts (OR 14.8, 95% CI 8.6-25.4, p < 0.001). Using the GLMM, tick abundance was found to be significantly higher in cattle older than 3 years. The tick burden in the udder/scrotum was higher than that from the chest and leg/thigh of the cattle (GLMM, p < 0.05). The tick burden at the anal region was also significantly higher than the leg/thigh and chest. This study indicates that the preferred attachment sites of ticks on cattle are species-dependent and effective treatment with acaricides should take into consideration the udder/scrotum and anal regions as well as prioritizing older cattle.