Middle East DVEP - Armed Forces Pest Management Board

outside and during the day. Engorgement usually requires only a few minutes. Bitesmay cause extreme irritation and itching in human or animal hosts. In sensitive persons,black fly bites can cause an acute allergic response. These flies are anthropophilic butalso feed on cattle. Black flies are exophilic and not noted for entering human structures.After feeding, black flies fly to nearby shaded sites or protective vegetation.Black flies are strong fliers that can travel many kilometers (5 to 10 km or more) fromtheir home streams. It is estimated that strong winds could easily carry them anadditional 5 to 10 km from their breeding sites.Because most suitable streams flow primarily during the rainy season, the seasonaldistribution of black flies is usually short. In Yemen, this season lasts from April toAugust, primarily in the southwest part of the country bordering the Asir District of SaudiArabia.Vector Surveillance and Suppression. Control can rarely be achieved by directlyattacking the adult black fly. Adults are susceptible to insecticides but are usually toowidely dispersed for insecticidal spraying or fogging to achieve more than verytemporary local control. Black fly populations are most concentrated in the immatureaquatic stages. Control measures have been directed against black fly larvae with greatsuccess. Black fly larvae are susceptible to very low doses of many insecticides,including the biological control agent Bacillus thuringiensis (BTI). Aerial larviciding isusually necessary to treat rivers with extensive tributary systems. Reducing contactbetween black flies and military personnel is best achieved by using personal protectivemeasures, such as wearing protective clothing and headgear and applying repellents.(Appendix F).D. Bancroftian Filariasis.Bancroftian filariasis is caused by the nematode Wuchereria bancrofti, which normallyresides in the lymphatic system of infected humans. After 8 to 12 months, adult femaleworms release thousands of microfilariae into the circulatory system. Females continueto produce microfilariae over the next 15 to 18 years. Many individuals areasymptomatic in the early stages of infection. The disease develops slowly, withrecurrent episodes of fever and inflammation of the lymph glands. Microfilariae canobstruct the lymphatic system, causing the legs, breasts or scrotum to swell to grotesqueproportions, a chronic condition known as elephantiasis. This occurs only after repeatedinfections. Death of numerous microfilariae resulting from drug therapy may causesevere immune reactions.Military Impact and Historical Perspective. Microfilariae of W. bancrofti werediscovered in the blood of a patient in Brazil in 1866. This was the first discovery of apathogen that is transmitted by insects. Over 70 million people worldwide are estimatedto be infected by W. bancrofti, resulting in serious economic costs to developingcountries. The long incubation period and requirement for multiple infections over a longperiod of time before the appearance of clinical symptoms render chronic Bancroftianfilariasis of little medical significance to military operations. However, military124