New research shows that microscopic amoebae could allow the bubonic plague to hibernate in Colorado's soil for decades in between outbreaks before re-emerging.
Colorado is known for its outdoors. The majestic views and great recreational activities bring tourists from around the world to experience the Centennial State's natural splendor. But beneath the hiking trails and open space is a killer: the bubonic plague. Yes, the plague. Yersinia pestis. The Black Death. The disease responsible for killing millions of humans over the past 1,400 years. Coloradans have long known that the plague typically manifests in the state's prairie dogs and other rodent colonies. Every couple of years, there is a viral story about a pet dog digging up a plague-infected prairie dog and infecting a whole household. Late last year, veterinarians at the Colorado State University Veterinary Teaching Hospital tried, but failed, to cure a Broomfield family's dog that contracted the plague. Researchers were hopeful that they had found a way to combat the plague in Colorado by treating prairie dog colonies with vaccination regimens. But this strategy never accounted for where the disease would go once a colony is either vaccinated or eradicated. New research from the CSU Infectious Disease Research Center suggests that even if the prairie dog inoculation program succeeds, the disease will still be hibernating in Colorado's soil, waiting potentially years for the next outbreak.
The disease needs a host in order to survive. Many have posited that the lowest host organism for the Black Death is the common flea. In the Dark Ages, those fleas spread the plague across continents on the backs of stowaway rats. But now, researchers have identified an even lower, much more plentiful organism that could be serving as host for the plague: amoebae. Scientists collected soil samples in and around prairie dog burrows and then used a specially modified plague strain to test this hypothesis. The experiment was done in a controlled environment to make sure that the disease wouldn't spread. Scientists used a genetically modified strain that specifically glows green so that they could observe conditions under the microscope. What they saw was that the amoebae were ingesting the plague strains, confirming that the micro-organisms could -- in the right conditions -- allow the disease to lie dormant in the soil.
How long can the disease lie dormant? Researchers aren't sure. But what they do know is that these kinds of amoebae undergo transformations that allow them to lie dormant for up to 20 years before reanimating. The theory is that an amoeba's naturally dormant state could allow for the plague bacteria to evolve in between above-ground outbreaks. Amoebae are already understood to be disease "training grounds," providing a host that allows generally harmless bacteria to evolve into dangerous pathogens. With the plague already being a dangerous pathogen, the concern is that given the right conditions, these amoebae could allow the plague to lie dormant for years, evolve, and emerge at pandemic strength. What is even more terrifying is that we currently have no way to monitor plague activity in the soil. With prairie dog colonies, the disease is easy to track. Animals can be preemptively tested, and when there is an outbreak, die-offs tend to be unavoidable. But with the plague surviving inside of dormant soil amoebae, outbreaks would be unpredictable using current surveillance methods.
