Establishment of a GIS monitoring system for schistosomiasis japonica in Kofu, Japan.

Although the incidence of human infection with Schistosoma japonicum in Japan fell to zero in 1977, the threat of the possible re-emergence of the disease caused by this trematode still exists. Surveillance of the parasite's intermediate host, Oncomelania nosophora, in Kofu basin therefore began in 1996. A simple, new method for monitoring O. nosophora in an at-risk area in Kofu, which is based on a geographical information system (GIS), was established. At each monitoring site (of which there were 120 from 1996 until 2000, and 60 from 2001 until 2003), the O. nosophora in two quadrats, each measuring 25 x 25 cm, were collected. During the study, the exact location of each site was determined using a hand-held global-positioning system (GPS). This allowed all the sites to be digitally mapped, so that anyone with a hand-held GPS could and can reach each site. The snail and location data were processed using commercial GPS/GIS software packages and used to create a risk map for schistosomiasis re-emergence. Although all snails collected between 1996 and 2003 were uninfected, the proportion of investigated sites in which O. nosophora was detected increased from 36.7% in 1996 to 56.7% in 2003. The mean number of O. nosophora collected per snail-positive site fluctuated widely, between 8.2 and 57.4, in each calendar year. Over the study period there appeared to be a shift southwards in the areas with high densities of O. nosophora. The present results indicate that it is possible to utilize a GIS-based method for the long-term monitoring of the possible re-emergence of schistosomiasis japonica in Japan.