Seasonal variations of Onchocerciasis vector Simulium damnosum sensu lato in AbuHamed and Galabat foci in Sudan Arwa Elaagip B. Sc. (honors), M. Sc., PhD student University of Khartoum Faculty of Medical Laboratory Sciences

Introduction Onchocerciasis “River blindness” is a parasitic disease caused by the filarial worm Onchocerca volvulus. Transmitted by bites of female black fly Simulium damnosum complex and other Simulium vectors.

Introduction Patterns of seasonal changes of black flies are associated with the pronounced seasonal climatic variations. The prevalence of onchocerciasis is related to the presence and abundance of Simulium vector, therefore, studies of population dynamics is crucial for control/elimination program.

Objectives To measure the seasonal variations of Simulium damnosum s.l. flies using daily distribution, monthly densities and monthly biting rate (MBR) during wet and dry seasons in endemic villages in AbuHamed and Galabat foci in Sudan. To make scientific based recommendations on how best to reduce man-fly contact.

Materials and Methods Study areas: AbuHamed & Galabat

Materials and Methods Black fly adult collection The standard human landing capture method (Walsh, 1983) used to obtain adult flies for 5 days/month from endemic villages in AbuHamed and Galabat from 6:00 am – 7:00 pm during dry and wet seasons (2007/2008, 2009/2010). The monthly biting rate (MBR) was calculated (Davies & Crosskey, 1991; Seidenfaden et al. 2001). Statistical analysis The data were analyzed using SPSS program for t-student test.

Results Relative abundance of adult flies

Results Daily distribution

Monthly densities of S. damnosum s. l Monthly densities of S. damnosum s. l. in AbuHamed and Galabat foci during 2007-2008

Monthly densities of S. damnosum s. l Monthly densities of S. damnosum s. l. in AbuHamed and Galabat foci during 2009-2010

Statistical analysis of MBR In AbuHamed the highest density (9444; 2603) and MBR (58552.8; 16138.6 bites/person/month) were found in March 2007; 2010 respectively while the lowest density (0.0) and MBR (0.0 bites/person/month) were found in August-October. In Galabat the highest density (1138; 1163) and MBR (6828; 6978 bites/person/month) were found in September 2007; 2010 respectively, and the lowest density (0.0) and MBR (0.0 bites/person/month) in April-June. High significance difference in MBR between two foci (p=0.000).

Discussion The transmission of onchocerciasis varies within location and season in AbuHamed and Galabat foci in Sudan, and the comparison between the two breeding seasons in the two foci showed mark difference in seasonality.

Discussion Relative abundance Is high in AbuHamed compare to Galabat may be due to seasonality of Atbara River and less vegetation types which help in breeding of the flies. It is clear that the effect of rainfall on the abundance of flies during each year in the two foci.

Discussion Daily distribution The unimodal beak (10:00am-6:00pm) in AbuHamed may be synchronized with increased temperature (max 34.5°C,min 18.8°C) and human farming activity. The bimodal peak (6:00-10:00 am, 2:00-7:00pm) in Galabat might be due to decreased temperature (max 34.4°C, min 22.1°C), and coincides with the active farming periods, washing of clothes, grazing and drinking of livestock, catching and collection of drinking water in the area.

Discussion Monthly distribution In AbuHamed: wet flooding season (August- October) Zero number of flies, this may be due to high turbidity of water and the breeding sites were covered by high flooding water. In Galabat: wet rainy season (August- December) high numbers of flies, this may be to high oxygen contents found during rainy wet season.

Discussion This detailed information on human exposure in relation to vector seasonality, distribution and biting activity has generated base-line data on local ecological variations of onchocerciasis transmission which could determine the ultimate success of onchocerciasis control/elimination program and has obvious implications for planning operations in contrasted ecological situations in Sudan.

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