What Is Hookworm?

Hookworm is an intestinal parasite of humans that usually causes mild diarrhea or cramps. Heavy infection with hookworm can create serious health problems for newborns, children, pregnant women, and persons who are malnourished. Hookworm infections occur mostly in tropical and subtropical climates and are estimated to infect about 1 billion people -- about one-fifth of the world's population.

Some diseases occur mainly in certain climates or geographical regions of the world. These diseases are said to be endemic in the regions concerned. For example, African sleeping sickness, which is carried by the tsetse fly, is found mainly in the very hot, humid regions of Africa. Similarly, malaria, a disease spread by mosquitoes, is usually found in or near the marsh or stagnant water that provide breeding grounds for the insect. Other diseases may be seasonal - such as influenza, which tends to occur mainly in winter, or intestinal illnesses that result from food contamination in summer.

Hookworm disease has been recognized in northern fur seals since 1896 when F. A. Lucas described the worm from the intestine of a 3-month-old dead fur seal pup in the Pribilof Islands, Alaska. From the time of their description until the early 1980s, hookworms were highly prevalent in fur seal pups and were responsible for a substantial amount of pup mortality in the Pribilof Islands.

Currently, however, there is virtually no mortality associated with hookworms in Pribilof Island fur seal pups, but on San Miguel Island in the California Channel Islands, hookworm disease has become a major source of pup mortality.
The adult worm of both is about 10 mm long, pinkish-white in color, and curved into an S-shape or double hook. The females produce about 10,000-20,000 eggs per day. These eggs are passed out of the host's body in feces.

The eggs enter the soil, where they incubate. Afterabout 48 hours, the immature larval form hatches out of the eggs. These larvae take about six weeks to develop into the mature larval form that is capableof causing human infection. If exposed to human skin at this point (usuallybare feet walking in the dirt or bare hands digging in the dirt), the larvaewill bore through the skin and ride through the lymph circulation to the right side of the heart.

Hookworm infection has historically been undermined by the disproportionate number of impoverished people affected and by the insidious nature of the infection. However, this trend has slowly reversed. At the 54th World Health Assembly in 2001, a resolution was passed to encourage antihelmintic treatment in at-risk school-aged children by 2010 in an attempt to control morbidity.

At present, new international efforts are ongoing to reduce the impact of this parasitic infection, with promising progress being made, particularly in the development of a new chemotherapeutics and an effective vaccine.

Hookworm disease in humans: Necator americanus and Ancylostoma duodenale have similar life cycles and similar methods of causing illness. The adult worm of both Necator americanus and Ancylostoma duodenale is about 10 mm long, pinkish-white in color, and curved into an S-shape or double hook. Both types of hookworm have similar life cycles. The females produce about 10,000-20,000 eggs per day. These eggs are passed out of the host's body in feces. The eggs enter the soil, where they incubate. After about 48 hours, the immature larval form hatches out of the eggs.