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 [1]. 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 [4].
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 [6]. California closed the campground where the child stayed, and treated it with insecticide for four days before re-opening [5]. 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 [5]. Additionally, New Mexico has reported that a woman’s death in July is suspected to been a result of plague [5].
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 [7]. Rodents in two locations in Idaho have tested positive this year [8]. 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 [9].
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 [10]. Interestingly, the division of plague-endemicity, or ‘plague line’ appears to clearly follow the 100th meridian [10]. The widely-accepted cause for this threshold being the boundary of prairie dog distribution [11].
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 [12]. 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 [13]. Besides the pit-bull outbreak, Colorado has been seeing an uptick in cases – and officials are attributing it to climate [1]. 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 [1]. 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 [14]. Unfortunately the trend may not remain so straightforward, as it is unclear what could happen as climate change progresses [1].
[2] http://www.usnews.com/news/articles/2015/08/06/plague-kills-second-person-in-colorado
[3] http://www.abqjournal.com/292719/abqnewsseeker/new-mexico-logs-first-2013-plague-death.html
[5] http://www.nbcnews.com/health/health-news/yosemite-closes-two-campgrounds-after-plague-case-n410211
[6] http://www.cdph.ca.gov/Pages/NR15-056.aspx
[7] http://www.ksl.com/?nid=148&sid=35498521
[8] http://www.ktvb.com/story/news/health/2015/06/15/rodents-plague-southwest-idaho/71269628/
[9] http://www.washingtontimes.com/news/2015/may/15/4-plague-cases-10-tularemia-cases-in-new-mexico-th/
[10] http://www.livescience.com/51792-plague-united-states.html
[11] http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1609&context=greatplainsresearch
