Schistosomiasis

Schistosomiasis is a disease caused by parasitic Schistosoma sp., commonly called blood flukes. The eggs hatch in water, where they infect an intermediate snail host. After being liberated from the snails, they can infect humans who have contact (be it swimming, bathing, or washing cloths) with infected water. This parasite can penetrate through the skin and infect its host. After maturing for six weeks in its host's abdominal cavity, the worm reproduces and the eggs spread through the small intestine, urinary bladder, and liver, causing significant tissue damage and hemorrhaging. Accumulation over time can result in a chronic, debilitating disease that can be fatal (Ohio State University, 2001).

Schistosoma mansoni egg

All three images Courtesy of Ohio State's Parasitological Resources <http://www.biosci.ohio-state.edu/~parasite/home.html>

Schistosomiasis is second only to malaria in its impact on the human population as a vector-borne disease. More than 600 million people in 74 countries are living with the risk of schistosomiasis and over 200 million people are infected (Bergquist, 2001). The disease is distributed through most of Africa and parts of Asia, South America, and islands in the Caribbean (Ohio State University, 2001).

Several characteristics of this disease make it ideal for analysis with GIS. First, the endemicity of schistosomiasis is strongly influenced by environmental factors, which can be mapped using GIS (Editorial, 2001). Second, the life cycle of this disease aids in predicting its spreading patterns. It relies on water and a snail host to reach an intermediate life stage before it can infect humans (Bergquist, 2001).

A Schistosomiasis warning sign in Puerto Rico (Translated as Do Not Bathe Yourself Here. There is Bilharzia [the local term for the parasite]); Image Courtesy of the CDC (A)

The need for GIS research on schistosomiasis is reaching a critical point. Due to development of water resources and population growth, the disease is being spread into areas previously not infected (Bergquist, 2001). Additionally, major damming projects in Egypt, Ghana, and Senegal have increased the number of people becoming infected in Africa. In 2003, a damming of the Yangtse river in Central China is set to be completed which will significantly shift the patterns of schistosomiasis in that region (Editorial, 2001).

A few projects have used GIS to try to document the patterns of the schistosomiasis disease. Researchers successfully complied paper records in Egypt into GIS to try to locate hot spots along the canal system to target for parasite control (Kling, 1997). A study of the epidemiology of intestinal infections in Africa emphasized the effectiveness of GIS as spatial modeling tool. It was noted that GIS was able to incorporate environmental variables into analysis and provided a specific data towards parasite control (Brooker and Michael, 2000).

Additionally, a team of researchers are setting up a global network on the surveillance of schistosomiasis and other snail-borne diseases using GIS. They aim for research collaboration, data sharing, and increased access of information and GIS models in order to try and more effectively control these diseases. The central resource groups include the World Health Organization, the Food and Agriculture Association, Louisiana State University, and the Danish Bilharziasis Laboratory. They will found regional GIS networks in high-risk areas for schistosomiasis. The initiated web site can be found at http://www.gnosisGIS.org (Malone et al., 2001).