Middle East DVEP - Armed Forces Pest Management Board

Female worms can deposit from 300 to 2500 eggs per day. Adult worms live 3 to 7years, but life spans of 30 years have been reported. Only about 50% of the eggsproduced reach the bladder or intestine, where they are excreted in the urine and feces.The rest become lodged in the liver and other organs. The immunological reaction to theeggs is the primary cause of both acute and chronic clinical symptoms. The degree ofchronic disease is directly related to the number of eggs deposited in the tissues.After excretion in urine or feces, a schistosome egg hatches in fresh water, releasing asingle miracidium (first larval stage) that penetrates and infects an appropriate species ofsnail. The miracidium can survive as an infective free-living entity for less than a day.Miracidia undergo a complicated cycle of development involving several larval stages inthe snail, and after 30 to 60 days each gives rise to several hundred infective cercariae.Humans are the principal hosts for both S. mansoni and S. haematobium. In Saudi Arabiathe baboon, Papio hamadryas, may be an important reservoir. Baboons inhabit southernSaudi Arabia in large numbers and have been found naturally infected with S. mansoni.Vector Ecology Profiles.Biomphalaria arabica, Bulinus beccarii, Bu. wrighti and Bi. truncatus are theintermediate hosts of schistosomes in the Middle East. Schistosoma mansoni isassociated with Bi. arabica, while S. haematobium is associated with Bu. beccarii, Bu.wrighti and Bi. truncatus. In highly endemic areas, only a small percentage of snails(usually