While the CDC tallied 16 instances of human plague among U.S. residents in 2015, just four such cases were detected in 2016, according to PBS Newshour.
U.S. outbreaks of plague occur most often in Arizona, California, Colorado and New Mexico. In 2016, all four U.S. plague cases were located in New Mexico.
The bacteria responsible for the illness is called Yersinia pestis and cycles through rodents and the fleas they carry. In 2016, the CDC tested eight animals for plague. Only one was positive.
"Historically, CDC tested hundreds of animals and fleas each year," Paul Mead, MD, chief of the Epidemiology, Bacterial Diseases Branch within the CDC's Division of Vector-Borne Diseases, told PBS Newshour via email. "As state health laboratories, particularly in Arizona, California, Colorado and New Mexico, gained the ability to do their own testing, we've tested fewer samples."
New Mexico Public Health Veterinarian Paul Ettestad, DVM, told PBS Newshour pets are the primary transmitter of plague to humans in the state. After rodents carrying the bacteria die, the fleas then look for other sources for blood, which can sometimes be a family pet.
"A lot of these dogs or cats, they [pet owners] let them inside the house, they sleep in bed with people. It really looks like that's when it happens," said Dr. Ettestad.
There are three forms of plague caused by the Y. pestis bacteria: bubonic, septicemic and pneumonic. All three cause fever and weakness among other symptoms. Bubonic plague provokes swelling of the lymph nodes, septimcemic plague can cause skin and other tissues to turn black and die, and pneumonic plague can cause respiratory failure and shock. The pneumonic plague is the most deadly of the three with a 90 percent fatality rate.
According to PBS Newshour, the total mortality rate for untreated plague previously ranged from 66 percent to 93 percent but has been reduced to 16 percent thanks to the advent of antibiotics.
To learn more about plague, click here.
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