Bioterrorism experts are worried that drug-resistant plague could be used as a weapon

biological warfare

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.

Untreated patients with either of these conditions can develop pneumonic plague, the most serious form of the disease, which happens when the infection gets into the lungs. (There are also rare Y. pestis strains that first infect the lungs, which causes a patient to leap straight to the most contagious form of the disease). When an infected person coughs, droplets of the bacteria enter the air and can survive there for an hour or so. People in close contact with the patient are therefore most likely to be infected by these droplets, and in a nightmare scenario those individuals could further spread pneumonic plague.

As Boodman writes, plague is actually one of the oldest bioweapons out there:

"After all, the bacteria were being used as weapons long before anyone even knew to call them bacteria. Plague-infected corpses were catapulted over walls. Venetians plotted to distill deadly liquid from swollen lymph nodes. Japanese planes sprinkled a rainfall of infected fleas. If those with nefarious motives and technical expertise wanted to weaponize the bacteria today, they could."

As Johns Hopkins public health researchers note, both the US and Soviet Union developed ways to create the aerosolized version of the plague in the 1950s and 1960s.

The thought of any type of biological warfare between countries is scary, but journalist Wendy Orent describes an even more worrisome possibility in her history of the illness, "Plague: The Mysterious Past and Terrifying Future of the World's Most Dangerous Disease." According to the book, Dr. Ken Alibek, a Kazakh defector from a Soviet biological weapons project, has suggested that the program was able to produce plague weapons resistant to at least 10 common antibiotics. And that was before the modern advances in genetics that exist today.

There's currently no plague vaccine, according to the CDC, so we can only hope that such an untreatable strain is never seen.

If drug-resistant plague were released as a weapon, humans would risk reliving the terrifying history of the Middle Ages. As a Scottish account from then says, "[i]t generated such horror that children did not dare to visit their dying parents, nor parents their children, but fled for fear of contagion as if from leprosy or a serpent."

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