Yersinia pestis, the causative agent of plague, is a highly lethal vector-borne pathogen responsible for killing large portions of Europe’s population during the Black Death of the Middle Ages. In the wild, Y. pestis cycles between fleas and rodents; occasionally spilling over into humans bitten by infectious fleas. For this reason, fleas and the rats harboring them have been considered the main epidemiological drivers of previous plague pandemics. Human ectoparasites, such as the body louse (Pediculus humanus humanus), have largely been discounted due to their reputation as inefficient vectors of plague bacilli. Using a membrane-feeder adapted strain of body lice, Bland et al. show that the digestive tract of some body lice become chronically infected with Y. pestis at low levels of bacteremia; at higher bacteremia, a subset of the lice develop an infection within the Pawlowsky glands (PGs), a pair of putative accessory salivary glands in the louse head. Lice that developed PG infection transmitted Y. pestis more consistently than those with bacteria only in the digestive tract, supporting the hypothesis that they may have played a role in previous human plague pandemics and local outbreaks. The image shows a human body louse (green autofluorescence) with Yersinia pestis infection (orange/red) in the Pawlowsky glands.

Image Credit: David M Bland