Middle East DVEP - Armed Forces Pest Management Board

Cercariae are killed by exposure for 30 minutes to concentrations of chlorine of 1 ppm.Treating water with iodine tablets is also effective. Heating water to 50 o C for 5 minutesor allowing it to stand for 72 hours will render it free of infective cercariae. Waterpurification filters and reverse osmosis are effective in removing cercariae.Molluscicides may be applied area-wide or focally by preventive medicine teams toeliminate snails from aquatic areas likely to be used by military personnel. Consult TIM23, A Concise Guide for the Detection, Prevention and Control of Schistosomiasis in theUniformed Services, and TIM 24, Contingency Pest Management Pocket Guide, formolluscicide recommendations and application techniques. There is little evidence thatsnail intermediate hosts have developed resistance to commonly used molluscicides likeniclosamide. The absence of snails in an area does not preclude infection, since cercariaemay be transported considerable distance by currents and wave action.Control programs in the Middle East have concentrated on the elimination of snail hostsby the use of chemical molluscicides and the early detection and treatment of infectedcases. The incidence of schistosomiasis has been greatly reduced in many MiddleEastern countries. Prevalence declined in Saudi Arabia from 9.5% in 1983 to 1.8% in1988. However, migration of workers from areas where schistosomiasis is endemic, theinaccessibility of snail habitatats, limited public health resources, and new water resourcedevelopment projects such as dams and irrigation schemes have hampered control effortsin many countries. The provision of piped water to houses or installation of water tapsfor public use will help reduce human contact with infested water and interrupttransmission of infection.C. Onchocerciasis. (River Blindness)This is a chronic, nonfatal disease in which adult worms form fibrous nodules insubcutaneous tissues. Adult female worms can live for 15 years and produce thousandsof microfilariae that migrate through the skin, causing disfiguring skin lesions.Microfilariae invade other tissues and organs and may reach the eye, where their invasionand subsequent death cause visual disturbances and blindness. The parasite is a filarialnematode worm, Onchocerca volvulus. A related species, O. fasciata, occurs in camelsbut does not infect man.Military Impact and Historical Perspective. Onchocerciasis has had a devastatingimpact on villages in the savanna area of West Africa. In many places over 10% of thepopulation is blind. Because of limited exposure, the impact of onchocerciasis would beinsignificant during most military operations. The severity of disease depends oncumulative effects of repeated infection that could result in long-term health problems forcontinuously exposed troops. Knowledge of this could impact troop morale during anoperation. Prolonged infection in an endemic area would be required to developclinically severe disease. After infection, larvae grow into adult worms over a period ofmonths. Microfilariae are found in the skin a year or more after the infective bite, whichis usually long after military personnel have left an endemic area.Disease Distribution. About 95% of all cases worldwide occur in Africa, where thedisease is endemic over vast areas of tropical western and equatorial Africa between the121