The Black Death is Back?
On August 5th, Colorado reported it’s second plague death in 2015 and the state has seen four human cases so far this year . The two deaths in Colorado are the first deaths from plague in the United States since 2013, when a New Mexico man died [2-3]. The Colorado cases have all occurred in different counties, with the two deaths being in Pueblo and Larimer Counties [1,2,4]. Most recently, the city of Boulder reported its first plague case in over 20 years, after a man came in contact with a dead chipmunk in his yard .
However, Colorado is not alone in its plague affliction this year – California reported its first human case on August 6th. The case, a child from Los Angeles, is believed to have been exposed while camping in/around Yosemite National Park . California closed the campground where the child stayed, and treated it with insecticide for four days before re-opening . The California Health Department is now reporting that it will close a second campground for similar treatment after two dead squirrels tested positive for the plague . Additionally, New Mexico has reported that a woman’s death in July is suspected to been a result of plague .
Animal cases have also been reported elsewhere in the country. In July, a prairie dog colony in Uintah County, Utah was wiped out by the plague . Rodents in two locations in Idaho have tested positive this year . As of May, New Mexico had already reported four cases of plague in animals, of greatest concern, the animals include a domestic dog and cat .
Noticing a geographic trend to all these plague cases?
Almost all plague cases, in both humans and animals, occur in rural areas of the western United States . Interestingly, the division of plague-endemicity, or ‘plague line’ appears to clearly follow the 100th meridian . The widely-accepted cause for this threshold being the boundary of prairie dog distribution .
But what is causing a notable increase in cases for 2015?
So far this year, Colorado has yet to surpass the eight human plague case-total from 2014 . However, last year may not be representative of a trend for Colorado. As the Disease Daily previously reported, three of Colorado’s 2014 human cases were a result of occupational exposure to an infected dog and its owner, when the dog was brought in for treatment at a veterinary clinic . Besides the pit-bull outbreak, Colorado has been seeing an uptick in cases – and officials are attributing it to climate . The state has seen wetter winters and springs the past two years, which has lead to more lush vegetation and consequently, the possibility for thriving rodent populations . A burgeoning rodent population means more hosts for the fleas that transmit plague, and increased likelihood that humans will come in contact with either.
In a 2012 report from the U.S. Geological Survey, instances where plague jumped from rodents to humans could be attributed to the wet winters of El Niño years . Unfortunately the trend may not remain so straightforward, as it is unclear what could happen as climate change progresses .