The majority of hookworm infections in humans are caused by one of two species of hookworm: Old World hookworm, Ancylostoma duodenale; and New World Hookworm, Necator americanus. The common names, and even the scientific name N. americanus, imply that A. duodenale originated in the Eastern Hemisphere while N. americanus originated in the Americas.
In fact, both species of hookworm came from the Eastern Hemisphere and the geographical distinction in the names is an accident of history. Both of these parasitic worms are widely distributed today, but confined to the tropics and subtropics except for scattered pockets where climatic conditions support their survival.
Origin of Old World hookworm
Ancylostoma duodenale occurs today in Southeast Asia, China, India, northern Africa, southern Europe, and less commonly in North and South America and the Caribbean. It is thought to have evolved in Asia and spread from there through human migration. Ironically, this species may have arrived in the New World at the same time as N. americanus and could even have been first.
Hookworms, once thought to have been introduced to the Americas after the famous voyages of Christopher Columbus, were, in fact, present there in prehistoric times. Archaeological finds – hookworm eggs and larvae in mummies and coprolites (fossilized feces) – show that hookworms came with early arrivals to the New World, and suggest that those early arrivals took a fast sea route. Since they likely came from Asia, Southeast Asia or the South Pacific, these people could well have brought the hookworm that is thought to have originated in that part of the world.
Necator americanus and A. duodenale eggs and larvae cannot be differentiated by standard laboratory parasitology methods. It is even more difficult to speciate their remains in fossils and mummies; however, modern molecular studies will likely shed further light on this mystery.
Origin of New World hookworm
Necator americanus is much more widespread in the tropics and subtropics than A. duodenale and may have migrated to the Americas with early human migrants; however, it’s clear that its major introduction came with the slave trade beginning in the 1500s. Thousands of African slaves came to the New World and brought hookworms with them. Wherever the climatic conditions were right, the worms thrived and soon infected the white colonists as well.
In another ironic twist, the health effects of the worms on the whites tended to be more severe – probably because the black slaves had some degree of immunity to the parasite. The toll that hookworm disease had on the whites of the American south was horrific, and that is how the worm, not discovered until 1902, came to be called Necator americanus: American killer.
Sources:
Beaver, Paul Chester, Rodney Clifton Jung, and Eddie Wayne Cupp. 1984 Clinical Parasitology 9th ed. Philadelphia: Lea and Febiger
Cox, F. E. G. 2002 “History of Human Parasitology.” Clinical Microbiology Reviews, 15(4)
Gonçalves, Marcelo Luiz Carvalho, Adauto Araújo, and Luiz Fernando Ferreira. 2003 “Human Intestinal Parasites in the Past: New Findings and a Review.” Mem Inst Oswaldo Cruz, 98(Suppl.1).
Roberts, Larry S. and John Janovy Jr. Foundations of Parasitology 6th Ed. Boston: McGraw Hill, 2000.
Rosemary Drisdelle - Rosemary Drisdelle has been published many times as a nonfiction writer and several times as a poet. Her first book, Parasites: Tales of ...
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