Phytochemical screening and repellence potencies of bioactive molecules of plant extracts derived from Ocimum suave, Ocimum americanum and Eucalyptus citriodora against Anopheles gambiae.

Abstract

Background: Malaria poses a global threat to human health. It's a vector-borne disease of public health concern and affects the socio-economic status of people in developing countries. Malaria management faces many challenges namely, affordability, availability, and quality of drugs. Plants are considered a very significant resource in many parts of the world due to their variety of uses in treating diseases and ailments. Conventional drugs are expensive and not readily available. Repellents have been in use for the prevention of Anopheles bites, but all these have a myriad of negative effects to the user, such as allergy and dermatitis. This study sought to develop a plant-based Anopheles gambiae repellent for control of malaria, because it is eco-friendly and non-toxic.

Methods: The plant leaf samples: Ocimum americanum and Eucalyptus citriodora were collected from Mugui village in Tharaka Nithi County, Kenya, while Ocimum suave was harvested at Gacuru village in Meru County, Kenya. The samples were hydro-distilled using a Clevenger apparatus to obtain the essential oils. The experimental tests were done in a repellent testing chamber. The values of repellency action were determined over control at a p-value of 0.05 and 0.01 by one-way ANOVA and separated using Student-Newman-Keels at P ≤ 0.05 using Minitab software. The chemical analysis of the essential oils was done using a Gas Chromatography-Mass Selective detector instrument (GC-MSD). The human-bait method was used to assess the repellency efficacy of the essential oils and their blends against An. gambiae.

Results: The GC-MSD results revealed that the plants are endowed with terpenoids, such as 1,8-Cineole. β-Bisabolene, β-Pinene, α-Terpineol, and Geranial as the most abundant compounds in the samples. The blend of O. suave and O. americanum in the ratio of 1:1 was the most potent (100.00 ± 0.00) and compared well with the positive control Ballet™ (100.00 ± 0.00). The observation that the blend of O. suave and O. americanum was comparable to Ballet^™, suggests that this may be due to additive or synergistic effects of individual constituents.

Conclusion: This study revealed that these plants are endowed with bioactive compounds such as terpenoids and flavonoids that possess potent repellency against An. gambiae mosquitoes.