Transmission dynamics of Simulium damnosum in rural communities of Akwa Ibom State, Nigeria.

BACKGROUND & OBJECTIVES: Onchocerciasis is endemic in some parts of Akwa Ibom State, Nigeria. This study describes the entomological parameters of transmission in three rural communities of Akwa Ibom State, prior to ivermectin intervention in 2004. METHODS: Blackflies were caught using human bait and 90% of the flies were dissected for parity. All parous flies were further dissected for the presence of filaria larvae. Monthly and annual biting rate, and transmission potential were calculated using standard methods. RESULTS: A total of 4296 adult Simulium damnosum were caught on human bait, 4119 were dissected of which 208 (5.1%) were infected with Onchocerca volvulus larvae. Transmission parameters varied significantly (p < 0.05) in the three villages. Annual biting rates, ranged from 9490 to 11,218 bites per person per year. The annual transmission potential ranged from 131 to 189 infective larvae per person per year, monthly biting rate and monthly transmission potential varied significantly (p < 0.05) in the three villages. Transmission was highly seasonal occurring during the peak of rainy season from August to October. There was no transmission during the dry periods--November to March, and the early rainy periods--April to May. The diurnal biting activity of the fly exhibited a bimodal pattern with a morning peak (0900-1000 hrs) and a more marked evening peak (1600-1700 hrs). INTERPRETATION & CONCLUSION: The results indicate that there is a temporal and spatial variation in the transmission dynamics of S. damnosum in the study area.

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

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 percent (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 percent, in Idomido, Obiocamp, and Ikot Adaha respectively. The oil gave protection against the bite of S. damnosum for at least 3 h. A total of 710 adults S. damnosum were caught by individuals treated with Ocimum oil, as against 4296 caught by the control group. When the flies caught by the treated individuals were dissected none of them was infected with microfilariae of Onchocerca volvulus. Human-vector contact and onchocerciasis transmission could be reduced by the topical application of the volatile oil during the peak biting periods of the vector.