When you hear “Ring Around the Rosie,” what do you think of?

Yersinia pestis is its scientific name.  This infectious bacteria is better known as “the plague.”  It wiped out a third of Europe’s population in the 1300s after spreading from Asia along trading routes.  There, the plague was the catastrophe that brought down the Mongol Empire which had stretched from the Pacific Ocean to Ukraine; from the Russian steppe to India, wiping out 60% of the population in China.  You might be surprised to hear that this disease continues to occur sporadically throughout the world including in our own backyard.

Globally, there are about 2000 cases of plague reported to the World Health Organization annually.  In the last 10 years, there have been about 75 cases of plague in the United States with about 20 in Colorado.  Last month a family pet became infected with plague around the Larimer/Weld county border and in 2015, a Fort Collins youth died of plague.  Plague cases are usually concentrated in the “Four Corners” region which includes southwest Colorado.

The lifecycle of this bacteria depends on transmission from fleas which bite infected rodents and then pass the infection to other mammals when the same flea bites its next host.  Because of this dependence on transmission by fleas, there is a seasonal pattern with increased cases between late spring and late fall.  The symptoms of plague are initially similar to routine viral illnesses — fever, headache, chills — but within 48 hours unusual symptoms appear.  The “buboes” of bubonic plague are swollen lymph nodes near the site of the flea bite.  From there, the bacteria can spread to other parts of the body leading to swollen lymph nodes in other areas as well.  In addition to this presentation, a patient may present with Septicemic Plague in which the bacteria enters the bloodstream causing shock.  This then causes the extremities to turn black from intravascular coagulation.  The third presentation is pneumonic plague from inhalation of infected droplets or spread from bubonic or septicemic plague.  This is the only form that can pass person to person in routine contact.

Treatment with the plague is with intravenous or intramuscular antibiotics (gentamicin or streptomycin, usually) and if caught early in the course of infection, these are effective in curing the patient.  Despite its fearsome reputation, the plague has not developed resistance to antibiotics the way so many other bacterial species have.

I don’t know if you’ve noticed, but these insect transmitted infections seem to hold a special fascination for me.  I’ve always found infectious diseases to be the most interesting area of medicine.  So, over the year or so I’ve been writing for Pediatric Associates’ blog, I’ve returned to this topic time and again.  ZikaWest Nile and Powassan viruses are other insect transmitted animal reservoir infections I’ve written about.  I also wrote about insect repellents to help avoid the mosquito, flea and tick bites that transmit these infections to humans.