A study of helminths as novel vectors and reservoirs of human pathogens in the environment, using in-vivo real-time imaging systems

Here we detail a multidisciplinary exploratory study bringing together expertise in disease ecology/epidemiology, biomedicine, microbiology, environmental science, genomics and mathematical modelling to study the interactions between bacteria causing human disease (pathogens) and free-living helminths (nematode worms), both commonly found co-occurring in the soil. Previous work has shown that free-living helminths harbour a range of pathogens and that these could be transmitted to humans by accidental ingestion of free-living helminths or via parasitic helminths infected with human pathogens; termed helminth vectors. As such, our overall aim is to bring together experts from different fields to adopt a unique approach to experimentally test and monitor the association between pathogens and free-living helminths (parasitic and non-parasitic). This interaction may show a previously undiscovered mechanism of pathogen persistence and transmission in the environment, which in turn may lead to increased persistence and survival of pathogens in the soil with obvious implications for human health. In this study we will ascertain the advantages conferred to pathogens by associating with helminths. We ask questions such as 'does association of a pathogen with a worm protect the pathogen from environmental conditions that it otherwise would not survive, or offer protection against food sanitizers?' A natural progression is to then ask 'how does helminth vectoring alter persistence of the pathogen in the host population?' We will use model systems for our experiments because of their applicability to other systems and also for ease of work in terms of published techniques as well as availability of a range of phenotypic mutants useful to testing our hypotheses. We will use the free-living non-parasitic nematode Caenorhabditis elegans, because of its extensive use in genetic studies leading to a proliferation of established techniques. We will also use a parasitic helminth; the nematode Heligmosomoides polygyrus, a common parasite of wild mice. The bacteria used in the study will be Salmonella typhimurium and E. coli O157, which both cause severe gastrointestinal infections in humans and are common in the soil. In our study we plan to use a novel monitoring system; that of bioluminescent reporter bacteria. To discover whether these bacteria can be spread to humans and animals by small soil dwelling nematode worms, we will use genetically modified Salmonella and E. coli O157 that express the lux genes so that they are self-bioluminescent. The modified bacteria emit light when they are alive and can therefore be seen within the organism they are infecting, whether that is a worm or a larger organism, such as a mouse, which feeds on the bacteria. This gives us a novel method to study persistence and transmission of the disease causing (pathogenic) bacteria in the environment. This proposal aims to elucidate interactions between pathogenic bacteria, helminths (free-living and parasitic nematode worms), and the environmental conditions they experience and the implications this has for persistence of pathogenic bacteria in the environment and host. We aim to test the hypothesis that free-living helminths can be both environmental reservoirs and vectors of disease causing bacteria, using laboratory experiments, in conjunction with mathematical modelling. We posit that helminth vectors/reservoirs confer advantages to pathogenic bacteria that alter the way in which pathogens persist in the environment and may also alter the ability of these bacteria to cause human disease. The final part of the project will use DNA micro-array technology to investigate whether the bacteria become more infectious when they are carried by nematode worms. Our findings will have important implications for the dynamics and control of pathogens found in the environment, including human enteric pathogens and important livestock infections.