Plague Death in Arizona: 5 Things you Need to Know
Yesterday, Coconino County, Arizona reported the death of a man from pneumonic plague. Here are five things you need to know about it:
1. Yes, this really is the plague.
Yes, pneumonic plague really is caused by Yersinia pestis, the same bacteria responsible for the Black Death, the pandemic that killed tens of millions of people in 14th century Europe.
2. Thanks to modern medicine, we can cure the plague
But just because this is the same disease that killed half of Europe doesn’t mean you need to panic! Because we know many things that people in the 14th century didn’t, like the fact that bacteria exist and cause disease1. And how to kill (many) bacteria: namely, antibiotics. For the plague that typically means streptomycin.
3. Knowing how to treat the plague doesn’t mean the plague isn’t dangerous
Antibiotics aren’t a magic bullet though. They need to be given quite quickly because people with the plague can deteriorate rapidly. And the symptoms of plague can come on really quickly! Even the same day a person was infected. In the recent Arizona case, the patient died the same day they showed up at the hospital.
Antibiotic resistance is also a concern. This means that doctors might need to try several different medications before finding one that works. Which isn’t great when you need to act fast! And, because plague is so rare these days, there isn’t a lot of good recent scientific evidence on the best antibiotics to use.
4. There are three types of plague illness, but they’re all caused by the same plague
Another thing that makes the plague complicated, even today, is that there are three different ways it can cause illness.
The most common form is bubonic plague. 80% of all US plague cases ever recorded were bubonic. That’s probably the one you imagine when you think of the Black Death, and it causes huge swollen lymph nodes (typically near the site of infection). These are called buboes and give the bubonic form it’s name. If untreated, bubonic plague is typically 50-60% fatal. Despite that, if you had to get the plague, this is the type you’d want because the others are worse!
Pneumonic plague, which the individual in Arizona had, happens when the plague infects a person’s lungs. This can happen because a person inhaled contaminated air, or because the infection moved from a person’s lymph nodes to their lungs (secondary pneumonic plague). Regardless of how a person develops pneumonic plague, it’s almost always fatal if untreated. And it can lead to person-to-person transmission.
The last type of plague is septicemic plague. This is when the bacteria gets into a person’s bloodstream. Like pneumonic plague it is essentially 100% fatal if untreated. Also like pneumonic plague it can develop as a consequence of bubonic plague or as the main disease.
There’s also a fourth (bonus) type of plague called yersiniosis. But this is not actually caused by Yersinia pestis; instead it’s caused by some cousins: Yersinia enterocolitica, and Yersinia pseudotuberculosis. Yersiniosis is typically a gastrointestinal illness.
5. Plague (mostly) transmits to humans from animals
There are three main ways to get infected with the plague.
If you don’t know much more about the plague than a vague idea of the Black Death, you probably think transmission is from rats. And while rats (and other rodents) are a key part of the transmission chain, the real culprit is fleas. Flea bites are the most common way that the plague is transmitted both to humans and between animals. In Arizona, plague is endemic in prairie dogs and fleas who have fed on infected prairie dogs are the typical source of infection for both humans and for other animals, like rabbits, or pet cats and dogs. People who are infected via a flea bite typically develop bubonic or (less commonly) septicemic plague.
The plague can also be transmitted through contact with contaminated tissue or fluid from an infected animal (including eating contaminated meat). Some historians think that this may be one of the ways that the plague reached Europe (since the plague kills people so quickly, it doesn’t make sense for it to have made it’s way to Europe flea-by-flea!).
The last transmission route is respiratory. This requires that the infected individual have pneumonic plague. The evidence seems to suggest that exhaled plague is only infectious in the larger droplet-sized respiratory particles, which means that close contact is required for transmission. But, again, since it’s so rare the evidence is limited. But luckily, since pneumonic plague is rare, respiratory transmission is also rare. In fact, the last documented person-to-person respiratory transmission of plague in the US was in 1924!
Unfortunately, human-to-human isn’t the only type of respiratory transmission of plague. A key culprit of respiratory transmission in the US is pet cats! If a cat eats an infected rodent, it can become infected (see “contact with contaminated tissue”), and then when it snuggles up to it’s owner it can breath plague all over their face. Don’t let your indoor cats roam around outdoors!
Bottom line: Plague is very very rare in the US and pneumonic plague is even more rare, but it is something that can happen at any time. That means it’s important for public health agencies in at risk areas to be continuously monitoring wild animal populations. Because plague is endemic to the US Southwest. And endemic means someone is always working to control the disease.
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Or at least, most of us know this. Robert F Kennedy Jr doesn’t seem to be convinced that infectious diseases are caused by bacteria or viruses. Hopefully he doesn’t knock US science and medicine back to the 14th century!
Very insightful. Thanks very much for covering, Ellie!
Excellent discussion as usual. I used to live in that county but hadn’t heard about this case. Thanks so much!
P. S. Are you still at BU?