Pet monkeys could play a role in yaws eradication

Yaws is a tropical disease that occurs in the remotest and poorest regions of Africa, Southeast Asia and the Pacific region. It causes disfiguring skin lesions on the face, arms and legs. Untreated, the lesions develop into severe bone and cartilage damage and eventually irreparable deformations of the skeleton. The disease is transmitted from person-to-person by direct skin contact with infected lesions. The causal pathogen of yaws is the bacterium Treponema pallidum ssp. pertenue, a subspecies of the syphilis bacterium Treponema pallidum ssp. pallidum. In a recent study, an international research team, including Sascha Knauf from the German Primate Center, has detected antibodies against the bacterium in blood samples from various macaque species in Southeast Asia, which had close contact with humans. The scientists therefore assume that the disease can be transmitted not only from person-to-person, but also between humans and monkeys. This must be taken into account in combating the disease in the future (Emerging Infectious Diseases, 2017).

The World Health Organization (WHO) aims to eradicate yaws worldwide by 2020. A single tablet of the antibiotic azithromycin is enough to treat an infected person (Mitjà et al., The Lancet, 2012). However, the campaign’s current treatment strategy is based on the assumption that yaws occurs only in humans and has no natural reservoir in the animal kingdom. Our closed relatives, monkeys, however, could theoretically be infected with Treponemes.

Within the framework of the study, the scientists examined 734 blood samples from 13 different macaque species. The samples were taken from 1999 to 2012 in different Asian countries both from wild living and domesticated monkeys. In eleven of these blood samples, the researchers were able to detect antibodies against the Treponema bacterium (1.5 percent). These samples came from monkeys from Singapore as well as from the Indonesian islands of Bali and Sulawesi.

“The number of positive samples appears to be low at first,” says Sascha Knauf, scientist in the Pathology Unit at the German Primate Center and co-author of the study. “However, it is striking that the positively tested monkeys lived almost all as pets in close proximity to humans as well as the samples were collected in Indonesia during a yaws outbreak from 2001 to 2011. Thus, the animals probably may have been infected by humans.”

The fact that macaques are kept as pets is unfortunately not uncommon in Southeast Asia. The close physical contact with humans promotes a transmission of the disease from people to monkeys and the other way round. It has long been known that monkeys in Africa are considered a natural reservoir for the infection of humans with the Treponema bacterium (Knauf et al., Emerging Infectious Diseases, 2013).

“Our studies show that different species of monkeys can be infected wherever the disease is or was present in humans,” says Sascha Knauf. “A complete eradication of yaws in Asia will probably only be possible if not only humans, but also their pet monkeys are treated. This approach is known as a one-health approach, in which it is assumed that the health of humans, animals, and the environmental is connected which each other. Infected monkeys would otherwise pose a great risk for humans to get re-infected. In this case, a sustainable eradication of the pathogen would become difficult.”

Original publication:

Klegarth et al. (2017): Survey of Treponemal Infections in Free-Ranging and Captive Macaques, 1999–2012. Emerging Infectious Diseases, 23(5): 816-819. dx.doi.org/10.3201/eid2305.161838