Guinea worm: from Robert Leiper to eradication

Abstract

SUMMARYGuinea worm disease, dracunculiasis or dracontiasis, is an ancient disease with records going back over 4500 years, but until the beginning of the 20th century, little was known about its life cycle, particularly how humans became infected. In 1905, Robert Thomas Leiper was sent by the British colonial authorities to West Africa to investigate the spread of Guinea worm disease and to recommend measures to prevent it. While carrying out his investigations, he made important contributions to the aetiology, epidemiology and public health aspects of Guinea worm disease and provided definitive answers to many outstanding questions. First, he tested the validity of previous theories; second, he confirmed the role of water fleas, which he identified as Cyclops, as the intermediate hosts in the life cycle; third, he investigated the development of the parasite in its intermediate host; and fourth, he recommended measures to prevent the disease.[The crustacean Order Cyclopoida in the Family Cyclopidae contains 25 genera, including Cyclops which itself contains over 400 species and may not even be a valid taxon. It is not known how many of these species (or indeed species belonging to related genera) can act as intermediate hosts of Dracunculus medinensis nor do we know which species Fedchenko, Leiper and other workers used in their experiments. It is, therefore, best to use the terms copepod, or copopoid crustacean rather than Cyclops in scientific texts. In this paper, these crustaceans are referred to as copepods except when referring to an original text.]Leiper described the remarkable changes that took place when an infected copepod was placed in a dilute solution of hydrochloric acid; the copepod was immediately killed, but the Dracunculus larvae survived and were released into the surrounding water. From this, he concluded that if a person swallowed an infected copepod, their gastric juice would produce similar results. He next infected monkeys by feeding them copepods infected with Guinea worm larvae, and thus conclusively demonstrated that humans became infected by accidentally ingesting infected crustaceans. Based on these conclusions, he advocated a number of control policies, including avoidance of contaminated drinking water or filtering it, and these preventive measures paved the way for further research. The challenge to eradicate Guinea worm disease was not taken up until about seven decades later since when, with the support of a number of governmental and non-governmental organizations, the number of cases has been reduced from an estimated 3·5 million in 1986 to 25 in 2016 with the expectation that this will eventually lead to the eradication of the disease.

Climate Change and Water-Related Infectious Diseases

“…Dracunculus medinensis is transmitted by drinking water contaminated with copepods that contain the parasite larvae, and infections are easily controlled with simple measures. This disease is moving rapidly towards eradication under the supervision of the Carter Centre, with the World Health Organisation, UNICEF and CDC [131,132]. Although climate is likely to influence disease, the biggest problems in elimination have been organising surveillance in conflict areas [133], and the recent demonstration of a transmission cycle in dogs, particularly in Chad [134].…”

Dracunculiasis: water-borne anthroponosis vs. food-borne zoonosis

“…However, dogs could have been anticipated as definitive hosts having had a look at the literature. Dogs have repeatedly been considered not only a reservoir of the disease but also the best experimental animal model for reproducing human dracunculiasis (Moorthy & Sweet, 1936a, 1938; Muller, 1971; Adamson, 1988; Cairncross et al ., 2002; Tayeh et al ., 2017). Indeed, researchers have known for decades that dogs and other mammals can acquire D. medinensis .…”

Glasgow encounters with tropical diseases

“…Based on these observations he advocated a number of control policies, including avoidance of contaminated drinking water or filtering it, and these preventive measures have paved the way for further research. A serious challenge to eradicate Guinea worm disease was taken up about seven decades later and this is the subject of the paper by Ahmed Tayeh et al who described programmes sponsored by the World Health Organization, the Centers for Disease Control, the Carter Foundation and other organizations that have reduced the number of cases from 3·5 million in 1986 to 22 in 2016 with the expectation that this will eventually lead to the eradication of the disease (Tayeh et al 2017).…”

“…Leiper's scientific work with schistosomiasis and Guinea worm disease up to about 1915 has been extensively reviewed in this issue (see Stothard et al 2017;Tayeh et al 2017) No account of the contributions made by Scottish physicians and scientists would be complete without some mention of the explorer, David Livingstone. David Livingstone's name did not appear in the pantheon in the paper by Cox (2017a) mainly because he was not recognized for making any ground-breaking discoveries in the field of tropical diseases.…”