A study into the way plague spreads through prairie dog colonies in the western United States has yielded insights that could help explain outbreaks of plague, Ebola, and other diseases that can be transmitted by animals to humans.
The study, led by Dan Salkeld and Mike Antolin of Colorado State University in the United States, suggests that even deadly diseases may persist unnoticed in a population for years as infections, rather than jumping from another species immediately before an outbreak. In addition, the team says that investigations commonly launched after a human outbreak can yield misleading information about which host species were responsible. For instance, it seems that grasshopper mice and coyotes, which scavenge plague-killed black-tailed prairie dogs, may speed transmission of the plague-causing bacterium by acquiring and spreading the flea vectors. Thus, fleas can transmit plague faster than was once thought. According to the team, the disease can persist in wider prairie dog populations through repeated dispersal and reinvasion despite local outbreaks that can kill 95%-100% of the members of affected colonies.
The authors state that this ’slow, smouldering, cryptic disease transmission in animal populations prior to outbreaks in humans is… a hypothetical explanation for the persistence of pathogens.’ They say that oversimplification of the ways animal-borne diseases spread may lead to serious scientific errors, saying: “If disease outbreaks are sporadic and difficult to predict, a bias toward studies of the pathogen’s ecology during the peaks or aftermaths of the outbreaks will naturally arise.” In the case of Ebola virus, they argue, sampling of ‘fruit bats after human outbreaks may have biased subsequent investigations toward bat-Ebola virus ecology’, resulting in researchers’ possibly overlooking other species that could be involved, including nonhuman primates and ungulates. According to the authors: “A misplaced focus on a single animal host species may nullify efforts to create useful early warning monitoring programmes.”