China’s Hookworms Redux
A new Global Burden of Disease Study 2010 focusing on the health transitions in China confirms a lingering and severe public health impact from hookworm infection.
My visits to Shanghai and the Chinese National Institute of Parasitic Diseases (IPD) began almost 20 years ago in the winter of 1994. I was eager to work at the IPD – then a component of the Chinese Academy of Preventive Medicine (CAPM) later the Chinese Center for Disease Control and Prevention (CCDC) –- following their publication of an extraordinary parasite epidemiology study of incredible magnitude that may never be repeated. Beginning late in the 1980s and into the early 1990s Chinese parasitologists conducted fecal examinations on almost 1.5 million people across all provinces. The study first published in the English biomedical literature in the Southeast Asian Journal of Tropical Medicine and Public Health found that hundreds of millions of Chinese were infected with soil-transmitted helminths (STHs), including 194 million people with hookworm infection (‘hookworm’). Most of these infections were south of the Yangtze River, cutting across all of the southern provinces from East to West, and I felt the IPD was an ideal institute to begin the co-development of a prototype human hookworm vaccine.
Over the next decade China underwent explosive economic growth, with marked reductions in poverty especially in its urban centers and in the highly populated coastal provinces in the East. In 2002, I published an article, China’s Hookworms in The China Quarterly to describe how poverty reduction and urbanization in China’s eastern provinces paralleled reductions in the prevalence of hookworm, leaving behind severe poverty and a significant hookworm disease burden in the southwestern provinces of Guizhou, Sichuan, and Yunnan provinces, among others.
This past June experts from the Institute of Health Metrics and Evaluation at the University of Washington led by Christopher Murray, together with scientists and public health experts from the University of Melbourne and several important Chinese institutions (with support from the Bill & Melinda Gates Foundation) published a landmark study in Lancet assessing the leading causes of death and disability-adjusted life-years (DALYs) in China, together with a comparison of shifts in health indicators and disease burden since 1990. The Chinese Global Burden of Disease Study 2010 identified a significant rise of non-communicable diseases (NCDs) linked to powerful socioeconomic forces such as urbanization, rising incomes, and ageing over the two decade period between 1990 and 2010, with a commensurate reduction in many communicable diseases. Particularly dramatic declines included an 80 percent reduction in disease burden from lower respiratory infections and greater than a 50 percent reduction in China’s neglected tropical diseases (NTDs), but more than a 90 percent reduction in ascariasis and trichuriasis, i.e., the two major STH infections other than hookworm.
Today hookworm infection still accounts for almost one million DALYs lost annually in China, placing it on par with many neoplasms and NCDs and exceeded only by food-borne trematode infections (led by lung and liver fluke infections) as China’s most important NTD. Although there has been a 54 percent reduction in China’s hookworm disease burden since 1990, a significant amount of morbidity remains, presumably in the southwestern provinces I highlighted previously.
In Forgotten People, Forgotten Diseases, I discuss how the history of China since its 1949 liberation is notable for an impressive track record of eliminating some important NTDs including lymphatic filariasis, while simultaneously achieving a log-fold reduction in the number of cases of schistosomiasis. Through expanded use of anthelminthic drugs in addition to the socioeconomic forces described above, both ascariasis and trichuriasis now also seem to be on their way out. In contrast, could the recalcitrance of China’s hookworm problem suggest a need for new or improved control tools, possibly including a vaccine?