Despite initial attempts by WHO to eradicate yaws from Asia, several island nations in Asia continue to report active cases of the disease in humans.
A recent study screened macaques in Southeast Asia and demonstrated a low but noteworthy prevalence of treponemal infection in these animals.
Lisa Jones-Engel, PhD, from the University of Washington, Seattle, and colleagues published the results of their study in the May 2017 issue of Emerging Infectious Diseases, the Center for Disease Control and Prevention’s monthly peer-reviewed public health journal. Despite initial attempts by WHO to eradicate yaws from Asia, several island nations in Asia continue to report active cases of the disease in humans.
“As the World Health Organization (WHO) pushes for the second time to eradicate yaws, our results, as well as the studies coming out of Africa, suggest that monitoring the primates that co-exist with humans in affected parts of the world should be part of the global strategy,” said Dr. Jones-Engel in an interview with Contagion®.
Yaws is the most common nonvenereal treponemal disease and is caused by the bacterium Treponema pallidum subspecies pertenue. This neglected tropical disease is endemic in West Africa, Southeast Asia, and the Pacific, and is a significant public health problem. In addition, yaws is a chronic, relapsing disease that is spread by skin-to-skin contact, and manifests as lesions that predominantly affect skin, bones, and cartilage.
Studies have shown that African Old World Primates (OWPs) can be infected by T. pallidum and develop signs of yaws. Research has also demonstrated genetic similarity between the organisms that infect monkeys and those that can cause yaws in humans.
Dr. Jones-Engel and her team have been studying the movement of infectious agents at the human-primate interface for more than 15 years. “We focus on contexts like urban and temple macaques as well as pet macaques, because these monkeys have the most intense and long term contact with humans.” Their studies “have consistently shown that macaques are highly susceptible to a variety of human diseases,” she emphasized.
Macaques are OWPs that are native to Asia as well as northern Africa, and are susceptible to T. pallidum infection.
“Recognize that for decades we have used hundreds of thousands of macaques as biomedical models of human disease, because they are immunologically so similar to us,” said Dr. Jones-Engel. “These same species exist in the wild in Asia. We need to accept the concept that humans and primates constitute a single reservoir from which both can be infected.”
“My colleagues detected treponemes in baboons in Africa,” she noted, “and asked if I would screen my archive of monkey serum samples for evidence of exposure of macaques in Asia to treponemes.”
In their study, Dr. Jones-Engel and colleagues examined blood samples from 734 macaques from 13 species across Asia. Fewer than 2% (11) tested positive for the bacterium, and most of these were pet macaques on the island of Sulawesi in Indonesia, where a yaws outbreak among humans was active at the time of sampling.
The researchers also reviewed data from physical examinations of the macaques that were performed at the time of sampling. They found that 13 of the 734 macaques—including 2 of the seropositive animals from Sulawesi—had hypopigmentation on the palms of their hands and/or feet. Although rarely seen in yaws, hypopigmentation is a common manifestation of pinta, a disease caused by infection with T. carateum, which is closely related to T. p. pertenue.
The results of this study therefore show that pet macaques in Southeast Asia can be infected with Treponema spp. related to those that infect humans. Because of this, Dr. Jones-Engel emphasizes the need to develop a holistic approach to health, “particularly in Asia, where monkeys are often revered and embedded in the culture.”
Highlighting their behavioral and ecological flexibility, Dr. Jones-Engel described macaques as "Darwinian superstars" because they can readily adapt to changing environments. “Unlike most other primates, macaques can thrive in areas where humans alter the environment,” she said.
Dr. Jones-Engel and her team also recently received a grant from the University of Washington Global Initiative Fund. This will allow them to screen additional primates in areas of Southeast Asia that continue to be plagued by human cases of yaws.
“Macaques are the primates to watch. We need to develop effective management and conservation strategies for these amazing monkeys that have given so much for science,” she concluded.
Dr. Parry graduated from the University of Liverpool, England in 1997 and is a board-certified veterinary pathologist. After 13 years working in academia, she founded Midwest Veterinary Pathology, LLC where she now works as a private consultant. She is passionate about veterinary education and serves on the Indiana Veterinary Medical Association’s Continuing Education Committee. She regularly writes continuing education articles for veterinary organizations and journals, and has also served on the American College of Veterinary Pathologists’ Examination Committee and Education Committee.