Parasitic flatworm schistosomiasis much more debilitating than previously thought

Mar 6 2008

Public health researchers have found that the health burden of an Asian strain of the parasitic flatworm schistosomiasis is much more debilitating than previously thought.

In a new study, published March 5 in the open-access journal PLoS Neglected Tropical Diseases, the researchers calculate that the impact of symptoms associated with schistosomiasis japonica is 7 to 46 times greater than current global estimates. This is the first strain-specific study of the global disease burden of schistosomiasis, which is one of the most common infections in the world, infecting an estimated 207 million people in 76 primarily developing countries. The study 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 (Harvard School of Public Health, Boston, USA). “Current measures may severely underestimate the disability-related impact of the infection and need to be revised.”

Through its Global Burden of Disease project, the World Health Organization (WHO) estimates the incidence, prevalence, severity and duration of over 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. Policymakers 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 DALY score on a scale of 0 (perfect health) to 1 (death). But the global burden of schistosomiasis has not been examined in more than a decade.

In this new study, the researchers focused on evaluating schistosomiasis japonica, one of the three main forms of schistosomiasis, found in China and the Philippines. The team used data from the scientific literature and a decision-model approach to re-examine the disease burden. 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.

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.”