To determine the repellent activity of Ocimum gratissimum volatile oil against Simulium damnosum (blackflies), a 12 month (January-December 2003) field study was conducted in three onchocerciasis endemic communities (Idomido, Obio camp, and Ikot Adaha) in Ini Local Government Area of Akwa Ibom State, Nigeria. The result revealed that topical application of 20% (v/v) concentration of the oil with liquid paraffin as a base, reduced the biting rate of S. damnosum by 90.2, 81.6, and 79.7%, in Idomido, Obiocamp, and Ikot Insect-transmitted diseases remains a major source of morbidity and mortality globally. In Nigeria, Onchocerca volvulus the causative agent of onchocerciasis (river blindness), is transmitted primarily by the blackflies (Simulium damnosum) complex (WHO 1995, Aisen et al. 2004, Opara et al. 2005. Onchocerciasis is both a public health hazard and socio-economic problem of considerable magnitude in Nigeria (Opara et al. 2005). They cause itching and disfiguring skin disease, serious eye lesions, and blindness (WHO 1995). The habit of S. damnosum, crawling on the skin of the individual constitute an intolerable nuisance, their painful bite lead to blood loss and serve as portal for viruses, bacteria, protozoa, and nematodes which the flies may carry on their bodies.The strategy for control of onchocerciasis is based on destruction of the vector's larvae, prevention of vector migration, and contact with human host, killing the adult filarial and microfilarial worms in the human host. Several attempts have been made to use DDT, larvicide, and chlorinated hydrocarbon insectide in the control of blackflies. Despite a remarkable reduction in the blackfly population the epidemiological results are not impressive (Walsh 1970, WHO 1995. The strategy being used to control onchocerciasis in Nigeria is mass drug administration (MDA) through community directed treatment with ivermectin. Ivermectin has a positive effect in reducing microfilariae load in the infected individuals, it reduces transmission of infection, prevents onchocercal blindness, and skin disease (Boaten et al. 1998, Ndyomugyenyi et al. 2004.Control of the parasites vector though desirable, is not feasible in view of the expansive areas infested and the long flight range of the fly, which facilitates the reinvasion of treated communities by flies from untreated contagious communities (Aisen et al. 2004). The worldwide threat of arthropod-transmitted disease, with their associated morbidity and mortality underscores the need for effective insect repellent. The quest to make human less attractive to blackflies has stimulated research on blackfly behaviour and control. A reduction in human vector contact through repellent action would significantly reduce the transmission of infective larvae to human hosts.Extracts from plant sources have been shown to possess insecticidal (Iwuala & Osisiogu 1981, Pathake & Dixit 1988, Anyanwu & Uloko 1997, Oda et al. 1997, Ayanwu & Amefule 2001 and repellent (Bernard 1999, Tawatsin et al. 2001, Aisen et al. 20...
