Schistosomiasis More Debilitating Than Previously Estimated, Study Shows

The impact of symptoms associated with schistosomiasis japonica is 7 to 46 times greater than current global estimates, the Brown research team found. This is the first strain-specific study of the global disease burden of schistosomiasis and is part of a growing body of evidence that the serious health effects of this common parasitic disease are far greater than previously estimated.

"Schistosomiasis has a detrimental impact on nutrition and growth and development and can lead to major organ damage and death," said lead study author Julia Finkelstein, a graduate of Brown's Program in Public Health who is now a graduate student at the Harvard School of Public Health. "Current measures may severely underestimate its disability-related impact of the infection and need to be revised."

Schistosomiasis is one of the most common infections in the world, infecting an estimated 207 million people in 76 primarily developing countries. Schistosoma parasites are disease-producing flatworms that live in snail-infested fresh water. People get infected from contact with contaminated water through daily activities such as swimming, bathing, fishing or rice farming. The flatworms enter the body through the skin and travel in the blood, causing symptoms ranging from anemia and diarrhea to internal bleeding and organ damage, and, in some cases, death.

Through its Global Burden of Disease project, the World Health Organization (WHO) estimates the incidence, prevalence, severity and duration of more than 130 major causes of illness, injury and death worldwide. This project is based on a statistical measure called the disability-adjusted life year (DALY), which is the number of years of life lost due to premature death and the years lost due to disability. Policy-makers use the data to help determine funding for prevention and treatment programs as well as research.

According to WHO estimates, the disease burden from schistosomiasis is low, with a 0.005 percent DALY score on a scale of 0 (perfect health) to 1 (death). The global burden of schistosomiasis has not been examined in more than a decade. In just the last few years, however, some researchers have published papers showing that the health burden of schistosomiasis may be greater than expected. The Brown team focused on evaluating Schistosoma japonicum, one of the three main forms of schistosomiasis. The strain is found in China and the Philippines and is the subject of intensive study by Brown faculty members over the last 20 years.

The team used data from the scientific literature and a decision-model approach to re-examine the burden of schistosomiasis. Finkelstein and her team arrived at a substantially higher disability impact for schistosomiasis japonica. Instead of a 0.005 score, they arrived at estimates of 0.098 to 0.186. The findings are consistent with the recently published estimates.

Stephen McGarvey, professor of community health and anthropology and director of the International Health Institute at Brown, is senior scientist on the project. McGarvey said the findings have important implications for global health policy. He notes that WHO's Global Burden of Disease program, headquartered at the University of Washington, is currently revising its report on global health -- and that researchers should reevaluate the disability scores for schistosomiasis and other chronic infectious diseases.

"We've got the best evidence yet that the burden of this disease is significantly underestimated," McGarvey said. "So we urgently need new data -- data that can help keep the disease in check by increasing funds for infection control and basic and translational research."

Journal reference: Finkelstein JL, Schleinitz MD, Carabin H, McGarvey ST (2008) Decision-Model Estimation of the Age-Specific Disability Weight for Schistosomiasis Japonica: A Systematic Review of the Literature. PLoS Negl Trop Dis 2(3): e158. doi:10.1371/journal.pntd.0000158

Other members of the research team include Mark Schleinitz, M.D., assistant professor of medicine at Brown, and Hélène Carabin, associate professor of biostatistics and epidemiology at the University of Oklahoma Health Sciences Center.

In a related expert commentary article also published in PLoS Neglected Tropical Diseases, Dr. Charles King (Case Western Reserve University, Cleveland, USA) , who was not involved in the study, predicted that, "Ultimately, these new measures of schistosomiasis-associated disability will translate into a greater priority to control schistosomiasis." Incorporating such new approaches and findings with old estimates will, he said, "be essential to providing a balanced and fair assessment of neglected tropical diseases, and for properly setting disease control priorities for these disabling diseases of poverty."

The National Institutes of Health and the National Science Foundation's Ecology of Infectious Diseases Program partly funded the work.