Heather R. Jordan

Mass mortality events and the role of necrophagous invertebrates

Scale is important in understanding and applying concepts in ecology. Historically, the mechanisms regulating necrophagous arthropod community structure have been well explored on a single vertebrate carcass. However, practically nothing is known of whether such findings can be extrapolated to cases where large numbers of carcasses have been introduced into an ecosystem at a single time point. With the increasing incidences of mass mortality events (MMEs), understanding how scale effects community assembly of necrophagous insects and the resulting bottom-up or top-down effects on the impacted ecosystem are of utmost importance. Unfortunately, MMEs are unpredictable, making their study nearly impossible within a robust experimental framework. The objectives of this paper are to provide a brief overview of what is known with regards to ecological responses to carrion, opine on the ramifications of MMEs on local communities, and provide a brief overview of knowledge gaps, avenues for future research, and a potential study systems for rigorous MME experiments.

Landscape and environmental influences on Mycobacterium ulcerans distribution among aquatic sites in Ghana

Buruli ulcer, caused by Mycobacterium ulcerans, is highly endemic in West Africa. While the mode of transmission is unknown, many studies associate Buruli ulcer with different types of water exposure. We present results from the largest study to date to test for M. ulcerans in aquatic sites and identify environmental attributes associated with its presence. Environmental samples from 98 aquatic sites in the Greater Accra, Ashanti, and Volta regions of Ghana were tested for the presence of M. ulcerans DNA by polymerase chain reaction. The proportion of aquatic sites positive for M. ulcerans varied by region: Ashanti 66% (N = 39), Greater Accra 34% (N = 29), and Volta 0% (N = 30). We explored the spatial distribution of M. ulcerans positive and negative water bodies and found no significant clusters. We also determined both highly localized water attributes and broad scale remotely sensed land cover and terrain environmental characteristics associated with M. ulcerans presence through logistic regression. Our results concur with published results regarding conditions suitable for M. ulcerans growth and associations with Buruli ulcer disease burden with regards to water characteristics and disturbed environments, but differ from others with regards to spatial associations and topographic effects such as elevation and wetness. While our results suggest M. ulcerans is an environmental organism existing in a specific ecological niche, they also reveal variation in the elements defining this niche across the sites considered. In addition, despite the causal association between Buruli ulcer and M. ulcerans, we observed no significant statistical association between case reports of Buruli ulcer and presence of M. ulcerans in nearby waterbodies.

Abiotic and Biotic Factors Regulating Inter-Kingdom Engagement between Insects and Microbe Activity on Vertebrate Remains

A number of abiotic and biotic factors are known to regulate arthropod attraction, colonization, and utilization of decomposing vertebrate remains. Such information is critical when assessing arthropod evidence associated with said remains in terms of forensic relevance. Interactions are not limited to just between the resource and arthropods. There is another biotic factor that has been historically overlooked; however, with the advent of high-throughput sequencing, and other molecular techniques, the curtain has been pulled back to reveal a microscopic world that is playing a major role with regards to carrion decomposition patterns in association with arthropods. The objective of this publication is to review many of these factors and draw attention to their impact on microbial, specifically bacteria, activity associated with these remains as it is our contention that microbes serve as a primary mechanism regulating associated arthropod behavior.

Mycobacterium ulcerans toxin, mycolactone may enhance host-seeking and oviposition behaviour by Aedes aegypti (L.) (Diptera: Culicidae)

The ecological functions of many toxins continue to remain unknown for those produced by environmental pathogens. Mycobacterium ulcerans, the causative agent of the neglected tropical disease, Buruli ulcer, produces a cytotoxic macrolide, mycolactone, whose function(s) in the environment remains elusive. Through a series of dual-choice behaviour assays, they show that mycolactone may be an interkingdom cue for the yellow fever mosquito, Aedes aegypti, seeking blood-meals as well as oviposition sites. Results provide novel insight into the evolution between bacteria and potential vectors. While further studies are needed to determine if mycolactone is an actual signal rather than simply a cue, this discovery could serve as a model for determining roles for toxins produced by other environmental pathogens and provide opportunities for developing novel strategies for disease prevention. The relationship between M. ulcerans, mycolactone, and Ae. aegypti further suggests there could be an amplification effect for the spread of pathogens responsible for other diseases, such as yellow fever and dengue.

A large-scale survey of the postmortem human microbiome, and its potential to provide insight into the living health condition

The microbiome plays many roles in human health, often through the exclusive lens of clinical interest. The inevitable end point for all living hosts, death, has its own altered microbiome configurations. However, little is understood about the ecology and changes of microbial communities after death, or their potential utility for understanding the health condition of the recently living. Here we reveal distinct postmortem microbiomes of human hosts from a large-scale survey of death cases representing a predominantly urban population, and demonstrated these microbiomes reflected antemortem health conditions within 24–48 hours of death. Our results characterized microbial community structure and predicted function from 188 cases representing a cross-section of an industrial-urban population. We found strong niche differentiation of anatomic habitat and microbial community turnover based on topographical distribution. Microbial community stability was documented up to two days after death. Additionally, we observed a positive relationship between cell motility and time since host death. Interestingly, we discovered evidence that microbial biodiversity is a predictor of antemortem host health condition (e.g., heart disease). These findings improve the understanding of postmortem host microbiota dynamics, and provide a robust dataset to test the postmortem microbiome as a tool for assessing health conditions in living populations.

Interkingdom Community Interactions in Disease Ecology

A key tenet of community ecology is the interactions of individual organisms contribute to the ecological structure and function of ecosystems. Within these networks of interacting organisms are those taxa important for human and animal health: disease systems defined by combinations of host, pathogen, reservoir, and vector or a subset of these components. While the simplest disease system is that of the host and pathogen, more complex systems include the direct interactions of a pathogen with other hosts and the microbial communities of those hosts, reservoirs, and sometimes vectors. Each of these disease system components is made up of species that directly and indirectly interact with other species in ways that affect their individual fitness, population biology, and role in communities of the ecosystem. This chapter recognizes the direct interactions of those species that make up the primary components of disease systems; however, the focus and examples provided relate to the more indirect interkingdom (or domain) interactions that impact disease system components. The examples provided include how microbial communities mediate invertebrate and vertebrate fitness and behavior, often in systems where the hosts play important roles in pathogen transmission and disease emergence. The potential mechanisms of these interkingdom interactions are also developed in detail, as the mechanisms of such interactions are likely the target of future studies that could directly inform disease management strategies. Based on these examples and mechanisms, the existing literature suggests there are likely undiscovered and complex interactions of species within communities that affect disease systems.

Buruli Ulcer: Case Study of a Neglected Tropical Disease

Neglected tropical diseases affect almost all human communities in rural areas of mostly developing nations. They have staggering negative effects on human health and local, regional, and national economies through mortality and morbidity. These diseases are neglected in many large-scale disease management and control programs and therefore do not recieve the research and funding attention of diseases with higher pharmaceutical potential. One such disease that epitomozies this situation is Buruli ulcer disease, also known as Mycobacterium ulcerans infection. This necrotizing skin disease results in severe and lasting morbidity that primarily affects children in rural regions of Africa and other tropical and subtropical regions. It is caused by a mycobacterium related to other pathogens that are the agents for two other diseases, leprosy and tuberculosis; however, this pathogen secretes myolactone which is a cytotoxic molecule that is both necrotizing and immunodepressive and is unique within its phylogeny. As a neglected tropical disease, research and funding has generally been sporadic and diffuse among countries and agencies, limiting scientific gains in better understanding some basic disease system tenants such as the mode of transmission and where the pathogen grows and replicates in the environment. These limitations compounded with the fact that it focally affects rural and poor populations have made the control of Buruli ulcer disease challenging. Further, disease emergence and reemergence is thought to be associated with landscape modifications such as deforestation, dam construction, farming, and mining, coupling this disease with degraded environmental conditions that may faciliate either the emergence or sustainability of other water-related diseases of the rural poor. This chapter generally reviews Buruli ulcer disease within the context of neglected tropical diseases in a way that integrates the research that occurs at the molecular and cellular level of pathogen and host investigation with broader ecosystem factors that include other biological interactions (e.g., food webs) considered to be important to elucidating transmission of the pathogen, all of which must be assessed in combination to achieve successful future disease management activities.