When two cases of plague popped up in New Mexico in June , they served as a reminder that the black death — yes, the plague — is still around.

The infection affects a handful of people in the US every year and between a few hundred and a few thousand annually around the world. Most people survive a plague infection these days, since it can almost always be treated with antibiotics.

But researchers, bioweapons experts, and governments still worry that the plague could be turned into a deadly bioweapon, especially if someone with terroristic intent were to find or engineer a strain that couldn’t be treated with common drugs.

The plague bacteria, Yersinia pestis, mutates regularly like any other organism. Drug-resistant strains have emerged several times in the wild. For that reason, as Stat News’ Eric Boodman explains in a profile of wildlife biologist and plague detective David Wagner, there’s always a scramble to identify plague strains when they emerge.

By analyzing the bacteria, researchers can see if the bacteria has picked up antibiotic-resistant genes and check whether the strain is wild or engineered.

Today, the CDC categorizes plague as one of the biological weapons agents of highest concern along with anthrax, smallpox, and viral fevers like Ebola and Marburg.

The scariest scenarios would involve an aerosolized version of the plague released like a cloud above a city or in a crowded area. The bacteria could be dumped from an airplane or even blown by a big fan, which would spark an outbreak of the pneumonic form of the illness — one that spreads rapidly through the air.

In 1970, World Health Organization researchers estimated that releasing a 50 kg aerosol cloud of plague bacteria over a city of 5 million could cause 150,00o plague cases, with between 80 and 100,000 hospitalizations and 36,000 deaths. That’s assuming that antibiotics worked, which is the case for all known wild strains circulating today.

Generally, bites from fleas carrying Y. pestis spread bubonic or septicemic forms of the plague, both of which cause fever and weakness. Bubonic plague results in painfully swollen lymph nodes; septicemic plague happens when the infection gets in the blood and causes skin and tissue to turn black and die. It can appear on its own or develop from bubonic plague. Continue reading.