The role of arthropods in the transmission of human pathogens.

Your Granny was right! Her battle to keep insects out of the kitchen was a valiant one and true!

It has long been known that arthropods such as flies, mealworms, cockroaches, ground beetles and centipedes can carry and transmit potenitially lethal organisms such as Salmonella spp., Listeria spp., Stapylococcus, spp., Shigella spp. and even the notorious E. coli strain EHEC 0157:H7 to name but a few. It is known that members of the Salmonellae family can be transovarially transmitted and bacteria can survive in the larvae and pupae of flies, highlighting the potential of insects as environmental reservoirs of bacteria. Recently, scientists working with Salmonella enteritidis  have demonstrated that flies, litter beetles and possibly centipedes may be potential vectors and environmental reservoirs of this bacterium and have suggested that these arthropods may be responsible for the maintenance of Salmonella on poultry farms. Such bacteria are not particularly harmful to these arthropods for a variety of reasons including the fact that the arthropod gut can mount a protective immune response including large quantities of antimicrobial peptides (AMPs) to protect against infection. It is also well known that arthropods are common contaminants of foodstuffs (we have all probably encountered a flour beetle at some time). If we combine the numbers of bacteria that may be transmitted to our food by arthropods with poor food hygiene, and storage practices we can end up with a food product that is hazardous to consumers. Surprisingly little work has been done on the potential of arthropods as vectors of foodborne pathogens, mainly because of the difficulty of bacterial identification. Advances in molecular biology have now successfully overcome this barrier and we have started reinvestigating the possibility that arthropods can be environmental reservoirs for a range of human pathogens.

Our preliminary findings demonstrate that this may well be true in the UK. We have identified a bacterium called Enterobacter sakazakii in the larvae of the stable fly, Stomoxys calcitrans. This bacteria is an emerging foodborne pathogen that can cause meningitis, sepsis and necrotizing enterocolitis in newborn infants. This organism particularly affects, but is not restricted to, premature or otherwise immunocompormised infants. Although an environmental reservoir and mode of transmission has not been clearly identified, a growing number of reports suggest that powdered milk-based infant formulas can be a vehicle for infection. More recently, there are reports that this bacterium also infects immunecompromised adults and there have been reports of multiple antibiotic resistance in this organism. We have isolated Enterobacter sakazakii from the guts of the larvae of the stable fly, demonstrating an environmental reservoir for E. sakazakii and raising the possibility that environmental contamination by insects may be important in the spread of this opportunistic organism. Read PDF of complete article here.

We also have preliminary evidence that other important human pathogens can be transmitted by insects and are widening our investigations to include a wide range of arthropods that are common stored product pests, livestock pests or common in the home, commercial kitchen, commercial food outlet or hospital environments.

This project has strong collaborative links with Dr. Henk Braig and Professor Mike Lehane, University of Wales, Bangor.