One tablet of ivermectin per year is enough to protect against river blindness. Health workers in the Ivory Coast have been battling a resurgence of the disease.
Issouf Sango AFP/Getty Images

Key Concepts

A group of seven tropical diseases, mostly caused by parasitic worms, afflict a billion impoverished people worldwide. They seldom kill directly but cause lifelong misery that stunts children’s growth, leaves adults unable to function to their fullest, and heightens the risk of other diseases.

Fortunately, they can be easily treated, often with a single pill. Various agencies and foundations are collaborating to deliver these drugs, although they have reached only about 10 percent of the population so far.

The U.S. has its own neglected parasitic diseases that affect millions of rural and urban poor.

In the north of Burkina Faso, not far to the east of one of the best-known backpacker destinations in West Africa, the Bandiagara Escarpment in Mali, lies the town of Koumbri. It was one of the places where the Burkina Ministry of Health began a mass campaign five years ago to treat parasitic worms. One of the beneficiaries, Aboubacar, then an eight-year-old boy, told health workers he felt perpetually tired and ill and had noticed blood in his urine. After taking a few pills, he felt better, started to play soccer again, and began focusing on his schoolwork and doing better academically.

The Burkina Faso program, which treated more than two million children, was both a success story and an emblem of the tragedy of disease in the developing world. For want of very simple treatments, a billion people in the world wake up every day of their lives feeling sick. As a result they cannot learn in school or work effectively.

Most people in richer countries equate tropical disease with the big three—HIV/AIDS, tuberculosis and malaria—and funding agencies allocate aid accordingly. Yet a group of conditions known collectively as neglected tropical diseases (NTDs) has an even more widespread impact. They may not often kill, but they debilitate by causing severe anemia, malnutrition, delays in intellectual and cognitive development, and blindness. They can lead to horrific limb and genital disfigurement and skin deformities and increase the risk of acquiring HIV/AIDS and suffering complications during pregnancy. They not only result from poverty but also help to perpetuate it. Children cannot develop to their full potential, and adult workers are not as productive as they could be.

Such diseases are not confined to developing nations. I estimate that millions of Americans living in poverty also suffer from NTD-like infections. Parasitic diseases such as cysticercosis, Chagas disease, trichomoniasis and toxocariasis occur with high frequency in our inner cities, post-Katrina Louisiana, other parts of the Mississippi Delta, the border region with Mexico, and Appalachia.

NTDs have plagued humankind for thousands of years. Historians have found accurate descriptions of many of them in ancient texts as diverse as the Bible, the Talmud, the Vedas, the writings of Hippocrates, and Egyptian papyri. What is new, however, is that donors, drugmakers, health ministries in low- and middle-income countries, the World Health Organization (WHO), and public-private partnerships are linking their efforts to combat the NTDs in a more coordinated and systematic way. Over the past half a decade the Bill & Melinda Gates Foundation, the Dubai-based sustainable development fund Legatum, and the U.S. and British governments have committed serious money, while major pharmaceutical companies have donated urgently needed NTD drugs. But the battle has only begun.

Like Leeches in Your Gut
The scale and extent of the global NTD problem are hard to take in. Almost every destitute person living in sub-Saharan Africa, Southeast Asia and Latin America is infected with one or more of these diseases. The illnesses last years, decades and often even a lifetime. The seven most common NTDs have the most devastating impact.

Three of them are caused by parasitic worms, also known as helminths, that live in the intestines. The large common roundworm, which results in ascariasis, afflicts 800 million people and the whipworm, which results in trichuriasis, 600 million people. These helminths rob children of nutrients, stunting their growth. Even worse are hookworms, which are found in 600 million people. These half-inch-long worms attach to the inside of the small intestine and suck blood, like an internal leech. Over a period of months or years they produce severe iron-deficiency anemia and protein malnutrition. Children with chronic hookworm anemia take on a sickly and sallow complexion and have trouble learning in school. More than 40 million pregnant women are also infected with hookworm, rendering them vulnerable to malaria or additional blood losses in childbirth. Their babies are born with low birth weights [see “Hookworm Infection,” by Peter J. Hotez and David I. Pritchard; Scientific American, June 1995].