The History of Hookworms and Hookworm Disease

Evolution, Discovery, and Benefits of a Common Intestinal Parasite

May 14, 2009

Hookworms have infected human intestines since prehistoric times. It's only in the last two centuries that humans have discovered and come to understand them better.

Two species of hookworm infect humans: Ancylostoma duodenale, or Old World hookworm, and Necator americanus, or New World hookworm. Despite their common names, both originated in the Old World: N. americanus originated in Africa, while Asia may be the homeland of A. duodenale. In any case, both are “heirloom” parasites of humans, evolving with us since the days of prehistoric hunter-gatherers.

Humans acquire hookworm infection when larvae in contaminated soil penetrate skin, or when animal flesh containing larvae is eaten without thorough cooking. (This second type of infection probably does not occur with N. americanus.) When humans settled in permanent communities, therefore, the parasites increased along with fecal contamination of the environment.

Prehistoric Evidence of Hookworm Disease

Most prehistoric evidence for hookworm disease comes from coprolites – fossilized human feces. Hookworm eggs have been identified in coprolites from North and South America, and Europe. The oldest, from Brazil, are more than seven thousand years old.

A number of coprolites have been found in the Americas that date from before European colonization. Not only does this mean that earlier arrivals of human beings to the continent brought the parasite, it also suggests how they came: because the hookworm life cycle requires tropical warm moist soil, it’s highly unlikely that bands of humans crossing the Bering land bridge in the north introduced the parasite. Hookworm probably came by sea.

Historic Records of Hookworm Disease

Early medical writings contain references to what was probably hookworm disease:

Angelo Dubini was the first to notice intestinal hookworms. He saw them while autopsying a woman who died in Milan in 1838. Thereafter, he looked for and found them at other autopsies.

In 1896 Arthur Looss was infecting guinea pigs orally when he accidentally dropped some of the solution on his own skin. The burning sensation that resulted prompted him to apply more and then check his own feces for eggs, which he found. Next, he applied larvae to a human leg that was about to be amputated, then examined the skin after amputation. He found that larvae had indeed penetrated the skin, thus proving how they invade human bodies.

Necator americanus was described in 1902 by C. W. Stiles, who found the eggs in samples from Texas. His discovery prompted the realization that hookworm was endemic in the southern United States, and causing widespread disease.

The Benefits of Hookworm

Surprisingly, recent medical research suggests that hookworm and our other “heirloom” parasites may moderate the human immune system, helping us avoid allergy and autoimmune disease. The theory is called the hygiene hypothesis.

Sources:

Clinical Parasitology 9th ed. Beaver, Paul Chester, Rodney Clifton Jung, and Eddie Wayne Cupp. Philadelphia: Lea and Febiger, 1984.

History of Human Parasitology. Cox, F. E. G. Clinical Microbiology Reviews, 15(4): 595-612, 2002.

Foundations of Parasitology 6th ed. Roberts, Larry S. and John Janovy Jr. Boston: McGraw Hill, 2000.

“Human Intestinal Parasites in the Past: New Findings and a Review.” Gonçalves, Marcelo Luiz Carvalho, Adauto Araújo, and Luiz Fernando Ferreira. Mem Inst Oswaldo Cruz, 98(Suppl.1): 103-118, 2003.

Parasites and Infectious Disease. Esch, Gerald W. Cambridge: Cambridge University Press, 2007.

“The Infectious Nature of Parasitology.” Mayberry, Lillian. Journal of Parasitology, 82(6): 855-864, 1996.

The copyright of the article The History of Hookworms and Hookworm Disease in Biology is owned by Rosemary Drisdelle. Permission to republish The History of Hookworms and Hookworm Disease in print or online must be granted by the author in writing.