An insect's ability to transmit disease is often influenced by interactions between the insect's host or the insect and the pathogen carried by the insect and by interactions among the pathogen and the other bacteria within the insect or its host. The plague, for example, is caused by a bacterium (the pathogen) carried by fleas (the vector), which are in turn housed by rodents (the host). Since insects like fleas and the fleas’ hosts contain communities of bacteria, not all of which are pathogens, the EU-funded FLEAMICROBIOME (Effects of ecological factors on bacterial communities of fleas) project aims to uncover what ecological conditions shape the structure of flea-borne bacterial communities. The project wants to determine which factors affect the make-up of bacterial communities in insect vectors and their hosts. To do this, researchers are looking at three potential influences in a rodent-flea model system: host diversity, host traits (e.g. age and reproductive status) and interspecific interactions among bacteria. To determine which microbes are present in these vectors and hosts, researchers analysed the genetic sequences of entire bacterial communities in fleas and blood collected from rodents. They found that two bacterial genera, Mycoplasma and Bartonella, were most common in both blood and flea samples and Wolbacia spp. infected all female fleas, but none of the male fleas. Researchers concluded that during the reproductive season adults were more likely to transmit Mycoplasma. Juveniles, on the other hand, were more likely to transmit Bartonella. However, the overall abundance of a certain vector-borne microbe was more likely to be determined by the abundance of endosymbiotic bacteria in the vector, abundance of other flea-borne microbes co-occurring in the vector and in the host blood and by seasonal changes, than by host characteristics. At a larger scale, the number of host species in the area affected the composition of bacterial species. Areas with more host species contained less Mycoplasma but more of the other bacterial species than species poor areas, increasing the risk of human infection by rare diseases. Identifying factors that affect the dynamics between hosts, vectors and their microbes will help prevent or control vector-borne diseases.
Bacteria, fleas, rodent, insects, diseases, host age, pathogen, vector, ecological communities, community structure, interspecific interactions, microbiome, species diversity