The effect of a combined approach to schistosomiasis control on the transmission of Schistosoma japonicum in Xingzi of Poyang Lake area, China.

The impact of a combined approach to schistosomiasis control from 1987 to 1989 and mass chemotherapy from 1992 to 1994 was studied in a rural community in Xingzi county in the northwest corner of Poyang Lake in Jiangxi Province, China. Humans, cattle, buffalo and pigs were known potential reservoirs of Schistosoma japonicum. Transmission occurs during water contact on and around seasonally flooded marshes that are used for grazing, the harvesting of grass and fishing. Humans and livestock underwent yearly selective mass chemotherapy, and snails were eliminated through ploughing and compacting of the marshland in the spring of 1988. Transmission was monitored through the determination of annual re-infection rates in samples of the human population, the annual examination of piles of feces from animals and humans in the marshland, the annual collection and examination of intermediate snail hosts, and the exposure to potentially polluted water and subsequent examination of sentinel mice. Schistosomiasis prevalence among humans and animals declined sharply as soon as mass chemotherapy was implemented. Snail density decreased even before mollusc control was started, possibly indicating a high variability of this indicator. The infection rates of snails and sentinel mice reached zero after a single application of mollusc control. The results underline the importance of single infected water buffalo for the transmission of schistosomiasis. Since the impact stopped for two years (1990-1991), the schistosomiasis prevalence rose quickly. Mass chemotherapy was an effective means to curb the prevalence of schistosomiasis in this area, but the effects were only maintained for one or two years in the marsh zone.