Yersinia pestis picked up several tricks. One is yersinia murine toxin (Ymt), a protein that helps it colonise the gut of fleas, its vectors between mammal hosts. Pictured are sections of flea guts, showing the thin oesophagus connecting to the larger midgut, after they were fed blood containing mutant Y. pestis, lacking Ymt. If acquired from mouse (top panels) or human blood, these bacteria struggle to take hold and are quickly eliminated. By contrast, when ingested with brown rat blood (below), which fleas take longer to digest, Y. pestis can persist even in the absence of Ymt. Variation between species suggests ancient strains lacking Ymt could already use fleas to move between certain hosts. Gaining Ymt then opened the door to much greater flea-borne transmission, between more species, highlighting how genetic innovations can alter the course of disease history.
Written by Emmanuelle Briolat
A researcher specialising in visual signals in Lepidoptera, camouflage and the effects of light pollution, Emmanuelle’s writing covers a range of topics, from biomedical research to children’s books about moth defences.