Browsing by Author "Merritt, R.W."
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Item Aquatic invertebrates as unlikely vectors of Buruli ulcer disease(Emerging Infectious Diseases 14(8): 1247-54, 2008) Benbow, M.E.; Williamson, H.; Kimbirauskas, R.; McIntosh, M.D.; Kolar, R.; Quaye, C.; Akpabey, F.; Boakye, D.; Small, P.; Merritt, R.W.Buruli ulcer is a necrotizing skin disease caused by Mycobacterium ulcerans and associated with exposure to aquatic habitats. To assess possible transmission of M. ulcerans by aquatic biting insects, we conducted a field examination of biting water bugs (Hemiptera: Naucoridae, Belostomatidae, Nepidae) in 15 disease-endemic and 12 non-disease-endemic areas of Ghana, Africa. From collections of 22,832 invertebrates, we compared composition, abundance, and associated M. ulcerans positivity among sites. Biting hemipterans were rare and represented a small percentage (usually <2%) of invertebrate communities. No significant differences were found in hemipteran abundance or pathogen positivity between disease-endemic and non-disease-endemic sites, and between abundance of biting hemipterans and M. ulcerans positivity. Therefore, although infection through insect bites is possible, little field evidence supports the assumption that biting hemipterans are primary vectors of M. ulcerans.Item Aquatic macroinvertebrate assemblages of Ghana, west Africa: Understanding the ecology of a neglected tropical disease(EcoHealth, 2014-06) Eric Benbow, M.; Kimbirauskas, R.; McIntosh, M.D.; Williamson, H.; Quaye, C.; Boakye, D.; Small, P.L.C.; Merritt, R.W.Buruli ulcer (BU) is an emerging, but neglected tropical disease, where there has been a reported association with disturbed aquatic habitats and proposed aquatic macroinvertebrate vectors such as biting Hemiptera. An initial step in understanding the potential role of macroinvertebrates in the ecology of BU is to better understand the entire community, not just one or two taxa, in relation to the pathogen, Mycobacterium ulcerans, at a large spatial scale. For the first time at a country-wide scale this research documents that M. ulcerans was frequently detected from environmental samples taken from BU endemic regions, but was not present in 30 waterbodies of a non-endemic region. There were significant differences in macroinvertebrate community structure and identified potential indicator taxa in relation to pathogen presence. These results suggest that specific macroinvertebrate taxa or functional metrics may potentially be used as aquatic biological indicators of M. ulcerans. Developing ecological indicators of this pathogen is a first step for understanding the disease ecology of BU and should assist future studies of transmission. © 2013 International Association for Ecology and Health.Item Distribution of Mycobacterium ulcerans in Buruli ulcer endemic and non-endemic aquatic sites in Ghana(Public Library of Science, 2008) Williamson, H.R.; Benbow, M.E.; Nguyen, K.D.; Kimbirauskas, R.K.; Beachboard, D.C.; McIntosh, M.D.; Quaye, C.; Ampadu, E.O.; Boakye, D.; Merritt, R.W.; Small, P.L.C.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. © 2008 Williamson et al.Item Ecology and Transmission of Buruli Ulcer Disease: A Systematic Review(Neglected Tropical Diseases, 2010) Merritt, R.W.; Walker, E.D.; Small, P.L.C.; Wallace, J.R.; Johnson, P.D.R.; Benbow, M.E.; Boakye, D.A.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.Item Interaction of mycobacterium ulcerans with mosquito species: Implications for transmission and trophic relationships(Applied and Environmental Microbiology, 2010-09) Wallace, J.R.; Gordon, M.C.; Hartsell, L.; Mosi, L.; Benbow, M.E.; Merritt, R.W.; Small, P.L.C.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 (Gerrldae), 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. Copright © 2010, American Society for Microbiology. All Rights Reserved.Item Mycobacterium ulcerans Fails to Infect through Skin Abrasions in a Guinea Pig Infection Model: Implications for Transmission(Public Library of Science, 2014) Williamson, H.R.; Mosi, L.; Donnell, R.; Aqqad, M.; Merritt, R.W.; Small, P.L.C.Transmission of M. ulcerans, the etiological agent of Buruli ulcer, from the environment to humans remains an enigma despite decades of research. Major transmission hypotheses propose 1) that M. ulcerans is acquired through an insect bite or 2) that bacteria enter an existing wound through exposure to a contaminated environment. In studies reported here, a guinea pig infection model was developed to determine whether Buruli ulcer could be produced through passive inoculation of M. ulcerans onto a superficial abrasion. The choice of an abrasion model was based on the fact that most bacterial pathogens infecting the skin are able to infect an open lesion, and that abrasions are extremely common in children. Our studies show that after a 90d infection period, an ulcer was present at intra-dermal injection sites of all seven animals infected, whereas topical application of M. ulcerans failed to establish an infection. Mycobacterium ulcerans was cultured from all injection sites whereas infected abrasion sites healed and were culture negative. A 14d experiment was conducted to determine how long organisms persisted after inoculation. Mycobacterium ulcerans was isolated from abrasions at one hour and 24 hours post infection, but cultures from later time points were negative. Abrasion sites were qPCR positive up to seven days post infection, but negative at later timepoints. In contrast, M. ulcerans DNA was detected at intra-dermal injection sites throughout the study. M. ulcerans was cultured from injection sites at each time point. These results suggest that injection of M. ulcerans into the skin greatly facilitates infection and lends support for the role of an invertebrate vector or other route of entry such as a puncture wound or deep laceration where bacteria would be contained within the lesion. Infection through passive inoculation into an existing abrasion appears a less likely route of entry. © 2014 Williamson et al.