Detection of Mycobacterium ulcerans in the Environment Predicts Prevalence of Buruli Ulcer in Benin

Abstract

Background Mycobacterium ulcerans is the causative agent of Buruli ulcer (BU). In West Africa there is an association between BU and residence in low-lying rural villages where aquatic sources are plentiful. Infection occurs through unknown environmental exposure; human-to-human infection is rare. Molecular evidence for M. ulcerans in environmental samples is well documented, but the association of M. ulcerans in the environment with Buruli ulcer has not been studied in West Africa in an area with accurate case data.Methodology/Principal FindingEnvironmental samples were collected from twenty-five villages in three communes of Benin. Sites sampled included 12 BU endemic villages within the Ouheme and Couffo River drainages and 13 villages near the Mono River and along the coast or ridge where BU has never been identified. Triplicate water filtrand samples from major water sources and samples from three dominant aquatic plant species were collected. Detection of M. ulcerans was based on quantitative polymerase chain reaction. Results show a significant association between M. ulcerans in environmental samples and Buruli ulcer cases in a village (p = 0.0001). A “dose response” was observed in that increasing numbers of M. ulceran- positive environmental samples were associated with increasing prevalence of BU cases (R2 = 0.586).Conclusions/SignificanceThis study provides the first spatial data on the overlap of M. ulcerans in the environment and BU cases in Benin where case data are based on active surveillance. The study also provides the first evidence on M. ulcerans in well-defined non-endemic sites. Most environmental pathogens are more broadly distributed in the environment than in human populations. The congruence of M. ulcerans in the environment and human infection raises the possibility that humans play a role in the ecology of M. ulcerans. Methods developed could be useful for identifying new areas where humans may be at high risk for BU.

Experimental Survival of Mycobacterium ulcerans in Watery Soil, a Potential Source of Buruli Ulcer

“…Indeed, the inoculum we used is in the range of what has been reported in the field. 3 Later, field investigation in Benin detected M. ulcerans DNA in 12/46 (26.1%) soil samples at higher inoculum levels than those measured in the water in the same area. 3 Furthermore, M. ulcerans DNA has been detected in groundwater sources.…”

“…3 Later, field investigation in Benin detected M. ulcerans DNA in 12/46 (26.1%) soil samples at higher inoculum levels than those measured in the water in the same area. 3 Furthermore, M. ulcerans DNA has been detected in groundwater sources. 3 Under these conditions, we observed a rapid drop in inoculum, indicating that the soil itself is most likely not a reservoir for M. ulcerans.…”

“…3 Furthermore, M. ulcerans DNA has been detected in groundwater sources. 3 Under these conditions, we observed a rapid drop in inoculum, indicating that the soil itself is most likely not a reservoir for M. ulcerans. However, these data suggest that watery soil could be a transient infection source.…”

“…8,9 In addition, the M. ulcerans inoculum has been estimated to be 100-1,000 mycobacteria/mL in water, based on real-time polymerase chain reaction (RT-PCR) targeting IS2404. 3 This estimated inoculum level is three to four times lower than the levels reported for major waterborne human pathogens such as Vibrio. 10 We have recently shown that Mycobacterium tuberculosis, a Mycobacterium that is phylogenetically closely related to M. ulcerans, retains its infectivity after an extended stay in soil.…”

“…1 Epidemiological studies conducted in West Africa traced to stagnant freshwater points. 2 Several studies have reported the detection of M. ulcerans DNA in stagnant freshwater 3,4 and aquatic environments. 5,6 Moreover, the only environmental M. ulcerans isolate was recovered from a water strider in Benin.…”