Longitudinal evaluation of repellent activity of Ocimum gratissimum (Labiatae) volatile oil against Simulium damnosum

Abstract

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...

Repellency of Hydrogenated Catmint Oil Formulations to Black Flies and Mosquitoes in the Field

“…1.5 ml dilution of each of three concentrations of each essential oil was applied at a rate of 1 ml per 500 cm 2 topically on each arm from elbow to finger tips (area approx 750 cm 2 ) and 2.5 ml on each leg from knee to foot (area approx 1250 cm 2 ) of test volunteers after disinfecting the treatment area skin with alcohol (Das et al 1985;Usip et al 2006). Two individuals (one male and female) applied only Helianthus annus oil and served as control for each test.…”

“…Their painful bit leads to the significant amount of blood loss and the wounds can cause secondary infections ( Fig. 1) by serving as passage for bacteria, viruses, protozoa and nematodes etc., which the fly may carry on their bodies (Usip et al 2006). …”

“…The eradication of vector borne disease is primarily based on destruction of vector larvae, killing of adult parasite in host's body and preventing vector-host contacts (Killeen et al 2000;Usip et al 2006). A number of synthetic chemical agents have been employed to destroy the black flies larvae but epidemiological results don't seem impressive (Walsh 1970;WHO 1995).…”

“…Control of adult blackflies is most desirable but it is less feasible due to frequent migration and long flight range of vector (Aisen et al 2004). Thus there exists a need to explore effective repellents in order to make the human host less attractive to black flies (Usip et al 2006).…”

“…Plant derivatives have been demonstrated to possess anti-insects properties (Bhuyan et al 1974;Tawatsin et al 2001;Aisen et al 2004;Usip et al 2006;Malau and James 2008;Zahir et al 2009;Kamaraj et al 2010). However the information on repellent activity of essential oils against blackflies biting is very scanty.…”