Wild animals could hamper efforts to eradicate yaws disease

Global health officials are intensifying efforts to eradicate yaws, a disfiguring skin disease that infects more than 64,000 people a year in 14 African and southeast Asian countries. But some critics say that the plans could fail, because they don’t take account of discoveries in the past few years that wild primate populations harbour the bacterial infection. That could complicate or foil eradication efforts, they say.

Public-health officials met in Geneva, Switzerland, on 29–30 January to discuss how to expand the eradication programme in 6 of the 14 countries in which yaws is endemic. But they did not discuss the part played by wild animals. “Even if this is not the main cause of re-emerging yaws nowadays, it would jeopardize global eradication,” says Sascha Knauf, who studies neglected tropical diseases at the Leibniz Institute for Primate Research in Göttingen, Germany.

Five years ago, the World Health Organization (WHO) committed to eradicating yaws by 2020, motivated in part by the discovery that it can be treated using an easy-to-administer oral antibiotic, azithromycin. It estimated that the initiative would cost at least US$100 million. At the time, public-health officials thought that the disease occurred only in humans. Eradicating a disease that affects only people is much easier than one that also occurs in pets and wild animals.

However, Knauf reported in 2013 and 20171,2 that gorillas, chimpanzees, baboons and smaller primates in several West and Central African countries, as well as macaques in Indonesia, were infected with the same bacterium that causes yaws (Treponema pallidum subsp. pertenue).

Primate problem

Epidemiologist Michael Marks at the London School of Hygiene and Tropical Medicine, who attended the workshop, says that the WHO has not addressed the threats posed by wild primate populations to the eradication of yaws. But he says that scientists have not yet shown that humans can catch the disease from primates. Even so, “it would be remiss not to pay attention to it.”

A similar problem arose during the decades-long programme to eradicate Guinea worm disease in 2010, when public-health officials learned that dogs and possibly other animals can carry the parasite (Dracunculus medinensis). Health authorities have had to invest in a public information scheme and extra monitoring and treatment, and the disease has yet to be eradicated.

The WHO is still waiting for proof that animals are transmitting yaws to humans, says its medical officer for the disease, Kingsley Asiedu. In the meantime, Asiedu says, “We are not taking that into account, because there has not been proof of an epidemiological link between those yaws-like cases that have been found in primates and in humans.”

First published by Nature: [html] [pdf]