M. Eric Benbow

Ecology and transmission of Buruli ulcer disease: a systematic review.

Buruli ulcer is a neglected emerging disease that has recently been reported in some countries as the second most frequent mycobacterial disease in humans after tuberculosis. Cases have been reported from at least 32 countries in Africa (mainly west), Australia, Southeast Asia, China, Central and South America, and the Western Pacific. Large lesions often result in scarring, contractual deformities, amputations, and disabilities, and in Africa, most cases of the disease occur in children between the ages of 4–15 years. This environmental mycobacterium, Mycobacterium ulcerans, is found in communities associated with rivers, swamps, wetlands, and human-linked changes in the aquatic environment, particularly those created as a result of environmental disturbance such as deforestation, dam construction, and agriculture. Buruli ulcer disease is often referred to as the “mysterious disease” because the mode of transmission remains unclear, although several hypotheses have been proposed. The above review reveals that various routes of transmission may occur, varying amongst epidemiological setting and geographic region, and that there may be some role for living agents as reservoirs and as vectors of M. ulcerans, in particular aquatic insects, adult mosquitoes or other biting arthropods. We discuss traditional and non-traditional methods for indicting the roles of living agents as biologically significant reservoirs and/or vectors of pathogens, and suggest an intellectual framework for establishing criteria for transmission. The application of these criteria to the transmission of M. ulcerans presents a significant challenge.

A Major Role for Mammals in the Ecology of Mycobacterium ulcerans

Background Mycobacterium ulcerans is the causative agent of Buruli ulcer (BU), a destructive skin disease found predominantly in sub-Saharan Africa and south-eastern Australia. The precise mode(s) of transmission and environmental reservoir(s) remain unknown, but several studies have explored the role of aquatic invertebrate species. The purpose of this study was to investigate the environmental distribution of M. ulcerans in south-eastern Australia. Methodology/Principal Findings A range of environmental samples was collected from Point Lonsdale (a small coastal town southwest of Melbourne, Australia, endemic for BU) and from areas with fewer or no reported incident cases of BU. Mycobacterium ulcerans DNA was detected at low levels by real-time PCR in soil, sediment, water residue, aquatic plant biofilm and terrestrial vegetation collected in Point Lonsdale. Higher levels of M. ulcerans DNA were detected in the faeces of common ringtail (Pseudocheirus peregrinus) and common brushtail (Trichosurus vulpecula) possums. Systematic testing of possum faeces revealed that M. ulcerans DNA could be detected in 41% of faecal samples collected in Point Lonsdale compared with less than 1% of faecal samples collected from non-endemic areas (p<0.0001). Capture and clinical examination of live possums in Point Lonsdale validated the accuracy of the predictive value of the faecal surveys by revealing that 38% of ringtail possums and 24% of brushtail possums had laboratory-confirmed M. ulcerans skin lesions and/or M. ulcerans PCR positive faeces. Whole genome sequencing revealed an extremely close genetic relationship between human and possum M. ulcerans isolates. Conclusions/Significance The prevailing wisdom is that M. ulcerans is an aquatic pathogen and that BU is acquired by contact with certain aquatic environments (swamps, slow-flowing water). Now, after 70 years of research, we propose a transmission model for BU in which terrestrial mammals are implicated as reservoirs for M. ulcerans.

Aquatic invertebrates as unlikely vectors of Buruli ulcer disease.

Biting water bugs were not correlated with pathogen occurrence.

Unraveling an emerging disease associated with disturbed aquatic environments: the case of Buruli ulcer

Buruli ulcer (Mycobacterium ulcerans infection) is an emerging disease of developing tropical and subtropical countries. This environmental mycobacterium causes severe morbidity in communities associated with rivers and standing water bodies (particularly those created as a result of human environmental disturbance such as deforestation and agriculture) and subsequent water quality changes. Neither the reservoir nor the mode of transmission is known, but data from laboratory studies suggest that biting aquatic insects may be involved. M ulcerans has been shown to colonize and grow within specific water bugs (Naucoridae), which then transmit M ulcerans to mice through their bites. PCR evidence suggests that the mycobacterium is present in water, biofilms of aquatic plants, detritus, invertebrates, and fish; however, systematic ecological studies that would provide a more comprehensive understanding of M ulcerans distribution in the environment have been lacking. Several hypotheses are explored in relation ...

Microbial community functional change during vertebrate carrion decomposition.

Microorganisms play a critical role in the decomposition of organic matter, which contributes to energy and nutrient transformation in every ecosystem. Yet, little is known about the functional activity of epinecrotic microbial communities associated with carrion. The objective of this study was to provide a description of the carrion associated microbial community functional activity using differential carbon source use throughout decomposition over seasons, between years and when microbial communities were isolated from eukaryotic colonizers (e.g., necrophagous insects). Additionally, microbial communities were identified at the phyletic level using high throughput sequencing during a single study. We hypothesized that carrion microbial community functional profiles would change over the duration of decomposition, and that this change would depend on season, year and presence of necrophagous insect colonization. Biolog EcoPlates™ were used to measure the variation in epinecrotic microbial community function by the differential use of 29 carbon sources throughout vertebrate carrion decomposition. Pyrosequencing was used to describe the bacterial community composition in one experiment to identify key phyla associated with community functional changes. Overall, microbial functional activity increased throughout decomposition in spring, summer and winter while it decreased in autumn. Additionally, microbial functional activity was higher in 2011 when necrophagous arthropod colonizer effects were tested. There were inconsistent trends in the microbial function of communities isolated from remains colonized by necrophagous insects between 2010 and 2011, suggesting a greater need for a mechanistic understanding of the process. These data indicate that functional analyses can be implemented in carrion studies and will be important in understanding the influence of microbial communities on an essential ecosystem process, carrion decomposition.

ROAD-SALT TOXICITY OF SELECT MICHIGAN WETLAND MACROINVERTEBRATES UNDER DIFFERENT TESTING CONDITIONS

This study determined lethal dose levels of road salt on selected macroinvertebrates from a Michigan, USA wetland under different testing conditions and related those levels to in situ chloride concentrations of standing water habitats along multi-lane highways. We conducted simultaneous acute (24 and 96 h) and chronic (15 d) toxicity experiments using laboratory containers, containers adjacent to a wetland, and in situ modular field PVC microcosms. Data showed that Callibaetis fluctuans, Physella integra, Hyallela azteca, and Chaoborus americamus had relatively high tolerance to elevated road-salt levels. Depending on test condition, road-salt 96 h LC50 estimates ranged from greater than 5000 mg 1−1 (2558 mg 1−1 Cl−) to >10,000 mg 1−1 (4502 mg 1−1 Cl−) road salt for C. fluctuans and P. integra, respectively. For H. azteca and C. americanus, mortality was generally low at all salt concentrations, with road-salt 96 h LC50 estimates >10,000 mg 1−1, Chloride concentrations of 43 impacted Michigan wetlands ranged from to 2700 mg 1−1 Cl−1, with 75% <334 mg 1−1, indicating that macroinvertebrate LC50 chloride estimates for the study species are well above most concentrations of the 43 wetlands.

Buruli ulcer disease prevalence in Benin, West Africa: associations with land use/cover and the identification of disease clusters

BackgroundBuruli ulcer (BU) disease, caused by infection with the environmental mycobacterium M. ulcerans, is an emerging infectious disease in many tropical and sub-tropical countries. Although vectors and modes of transmission remain unknown, it is hypothesized that the transmission of BU disease is associated with human activities in or around aquatic environments, and that characteristics of the landscape (e.g., land use/cover) play a role in mediating BU disease. Several studies performed at relatively small spatial scales (e.g., within a single village or region of a country) support these hypotheses; however, if BU disease is associated with land use/cover characteristics, either through spatial constraints on vector-host dynamics or by mediating human activities, then large-scale (i.e., country-wide) associations should also emerge. The objectives of this study were to (1) investigate associations between BU disease prevalence in villages in Benin, West Africa and surrounding land use/cover patterns and other map-based characteristics, and (2) identify areas with greater and lower than expected prevalence rates (i.e., disease clusters) to assist with the development of prevention and control programs.ResultsOur landscape-based models identified low elevation, rural villages surrounded by forest land cover, and located in drainage basins with variable wetness patterns as being associated with higher BU disease prevalence rates. We also identified five spatial disease clusters. Three of the five clusters contained villages with greater than expected prevalence rates and two clusters contained villages with lower than expected prevalence rates. Those villages with greater than expected BU disease prevalence rates spanned a fairly narrow region of south-central Benin.ConclusionOur analyses suggest that interactions between natural land cover and human alterations to the landscape likely play a role in the dynamics of BU disease. For example, urbanization, potentially by providing access to protected water sources, may reduce the likelihood of becoming infected with BU disease. Villages located at low elevations may have higher BU disease prevalence rates due to their close spatial proximity to high risk environments. In addition, forest land cover and drainage basins with variable wetness patterns may be important for providing suitable growth conditions for M. ulcerans, influencing the distribution and abundance of vectors, or mediating vector-human interactions. The identification of disease clusters in this study provides direction for future research aimed at better understanding these and other environmental and social determinants involved in BU disease outbreaks.

A Landscape-based Model for Predicting Mycobacterium ulcerans Infection (Buruli Ulcer Disease) Presence in Benin, West Africa

Mycobacterium ulcerans infection (Buruli ulcer [BU] disease) is an emerging tropical disease that causes severe morbidity in many communities, especially those in close proximity to aquatic environments. Research and control efforts are severely hampered by the paucity of data regarding the ecology of this disease; for example, the vectors and modes of transmission remain unknown. It is hypothesized that BU presence is associated with altered landscapes that perturb aquatic ecosystems; however, this has yet to be quantified over large spatial scales. We quantified relationships between land use/land cover (LULC) characteristics surrounding individual villages and BU presence in Benin, West Africa. We also examined the effects of other village-level characteristics which we hypothesized to affect BU presence, such as village distance to the nearest river. We found that as the percent urban land use in a 50-km buffer surrounding a village increased, the probability of BU presence decreased. Conversely, as the percent agricultural land use in a 20-km buffer surrounding a village increased, the probability of BU presence increased. Landscape-based models had predictive ability when predicting BU presence using validation data sets from Benin and Ghana, West Africa. Our analyses suggest that relatively small amounts of urbanization are associated with a decrease in the probability of BU presence, and we hypothesize that this is due to the increased availability of pumped water in urban environments. Our models provide an initial approach to predicting the probability of BU presence over large spatial scales in Benin and Ghana, using readily available land use data.

Interaction of Mycobacterium ulcerans with Mosquito Species: Implications for Transmission and Trophic Relationships

ABSTRACT Mycobacterium ulcerans is the causative agent of Buruli ulcer, a severe necrotizing skin disease that causes significant morbidity in Africa and Australia. Person-to-person transmission of Buruli ulcer is rare. Throughout Africa and Australia infection is associated with residence near slow-moving or stagnant water bodies. Although M. ulcerans DNA has been detected in over 30 taxa of invertebrates, fish, water filtrate, and plant materials and one environmental isolate cultured from a water strider (Gerridae), the invertebrate taxa identified are not adapted to feed on humans, and the mode of transmission for Buruli ulcer remains an enigma. Recent epidemiological reports from Australia describing the presence of M. ulcerans DNA in adult mosquitoes have led to the hypothesis that mosquitoes play an important role in the transmission of M. ulcerans. In this study we have investigated the potential of mosquitoes to serve as biological or mechanical vectors or as environmental reservoirs for M. ulcerans. Here we show that Aedes aegypti, A. albopictus, Ochlerotatus triseriatus, and Culex restuans larvae readily ingest wild-type M. ulcerans, isogenic toxin-negative mutants, and Mycobacterium marinum isolates and remain infected throughout larval development. However, the infections are not carried over into the pupae or adult mosquitoes, suggesting an unlikely role for mosquitoes as biological vectors. By following M. ulcerans through a food chain consisting of primary (mosquito larvae), secondary (predatory mosquito larva from Toxorhynchites rutilus septentrionalis), and tertiary (Belostoma species) consumers, we have shown that M. ulcerans can be productively maintained in an aquatic food web.

Examination of Nocturnal Blow Fly (Diptera: Calliphoridae) Oviposition on Pig Carcasses in Mid-Michigan

ABSTRACT The most common application of forensic entomology involves estimating a portion of the postmortem interval (PMI), which usually assumes that blow flies (Diptera: Calliphoridae) do not oviposit nocturnally. Research objectives were to (1) investigate blow fly nocturnal oviposition in relation to sunrise and sunset in Michigan; (2) evaluate abiotic variables postulated to affect blow fly oviposition; and (3) conduct laboratory experiments testing blow fly activity under complete darkness. In 2006, nocturnal oviposition was evaluated in relation to sunset by exposing pigs to fly colonization at 1-h intervals, beginning 2 h before and ending 2 h after sunset. This test was replicated in 2007; however, replicate pigs were placed in the field 2 h after sunset, and hourly observations were made into the following morning. Oviposition was never observed at night. In a laboratory experiment, Lucilia sericata (Meigen), never oviposited on liver hanging above or placed directly on the ground in a completely dark room, Another dark room laboratory study documented that adult flies launched into the air could not fly. This study documents that the probability of nocturnal oviposition on pig carcasses in Michigan was extremely low to nonexistent. These results should be considered when estimating a portion of the PMI in forensic entomological investigations.