Date Published: March 26, 2008
Publisher: Public Library of Science
Author(s): Heather R. Williamson, Mark E. Benbow, Khoa D. Nguyen, Dia C. Beachboard, Ryan K. Kimbirauskas, Mollie D. McIntosh, Charles Quaye, Edwin O. Ampadu, Daniel Boakye, Richard W. Merritt, Pamela L. C. Small, Mathieu Picardeau
Abstract: Mycobacterium ulcerans, the causative agent of Buruli ulcer, is an emerging environmental bacterium in Australia and West Africa. The primary risk factor associated with Buruli ulcer is proximity to slow moving water. Environmental constraints for disease are shown by the absence of infection in arid regions of infected countries. A particularly mysterious aspect of Buruli ulcer is the fact that endemic and non-endemic villages may be only a few kilometers apart within the same watershed. Recent studies suggest that aquatic invertebrate species may serve as reservoirs for M. ulcerans, although transmission pathways remain unknown. Systematic studies of the distribution of M. ulcerans in the environment using standard ecological methods have not been reported. Here we present results from the first study based on random sampling of endemic and non-endemic sites. In this study PCR-based methods, along with biofilm collections, have been used to map the presence of M. ulcerans within 26 aquatic sites in Ghana. Results suggest that M. ulcerans is present in both endemic and non-endemic sites and that variable number tandem repeat (VNTR) profiling can be used to follow chains of transmission from the environment to humans. Our results suggesting that the distribution of M. ulcerans is far broader than the distribution of human disease is characteristic of environmental pathogens. These findings imply that focal demography, along with patterns of human water contact, may play a major role in transmission of Buruli ulcer.
Partial Text: Mycobacterium ulcerans is the cause of Buruli ulcer, a severe necrotizing skin infection (Figure 1). Although Buruli ulcer is globally distributed, it is an emerging infection primarily in Australia and West Africa . The disease begins as a painless nodule or papule that, if left untreated, can lead to extensive ulceration that could cover 15% of the body . Though the disease is not usually fatal, Buruli ulcer can lead to profound morbidity, especially within rural areas of West Africa where treatment options are limited. Though sex and age are not seemingly risk factors, women and children between the ages 5 and 15 are most often infected. Incidence of Buruli ulcer has increased over the last several years. For instance, in Ghana, the number of new cases reported has been 685 in 2003, 1021 in 2004, 1097 in 2005, and 1010 in 2006. True incidence data, however is difficult to determine due to poor surveillance measures and case confirmation.
In this paper we present results from a large scale study of M. ulcerans in the environment. Although a number of studies have reported the presence of M. ulcerans in environmental samples from endemic regions ,,,, this is the first study where standardized ecological methods were used to reduce sampling bias, and the first to include longitudinal data from both Buruli ulcer endemic and non-endemic sties. One of the mysteries of Buruli ulcer is the close proximity of endemic and non-endemic villages. For example, whereas the disease is rarely reported from the Ga East district of the Greater Accra region in Ghana, it is endemic in the Ga West district despite the fact that endemic and non-endemic villages may be separated by only a few kilometers (Figure 3). Since the climate, rainfall, plant populations and ethnic groups in Ga East and Ga West are similar it has been difficult to understand the differential occurrence of Buruli ulcer within these regions.