We learned last week that campgrounds outside of Los Angeles were closed after a squirrel tested positive for plague. That sounds strange and scary. Does it mean we're all going to die? Well we are, eventually, but not of plague.
"The plague" has a bad name mainly because of the time in the fourteenth century when it killed a third of the human population. Later epidemics in the nineteenth century in China and India also killed millions. The U.S., though, has been relatively spared. In 1925, Los Angeles weathered a much smaller epidemic of bubonic plague — the bacterium having been introduced to the U.S. in 1900 via rat-infested ships from Asia — but that was the last urban epidemic.
Unlike other seemingly anachronistic infections, like smallpox — of which there hasn't been an organic case since 1977 — a handful of Americans still get diagnosed with the plague every year, mostly in the rural Southwest. We saw as many as 40 cases in 1983.
This is the very same plague that killed Europe so long ago, and it can be fatal, but it has a good prognosis when recognized and treated with antibiotics.
Counties Reporting Cases of Bubonic Plague, 1970-2012
Humans are incidental hosts of the bacteria that causes the plague (Yersinia pestis) which mainly affects other animals. It can and does regularly wipe out prairie dog colonies in a matter of days, maybe just to remind us how powerful it is. (Though it's often actually helpful to control prairie dog overpopulation.)
Bubonic plague is usually spread by getting bitten by an infected flea. When you get a bite, within a couple days you get a fever, headache, weakness, and one or more swollen, painful lymph nodes. The giant infected lymph node — the location of which also tells you where your flea bite was — is called a bubo. Which sounds cute but is not.
As the bacteria spread through the lymphatic system and sometimes the blood, our limbs can turn necrotic and black, and it can be deadly (Black Death).
There are still parts of the world where bubonic plague mortality rates are high. The World Health Organization records between 1,000 and 2,000 cases every year, though they're likely missing many that go unreported.
Cases of Bubonic Plague, 2000-2009
The California campgrounds where the offending squirrel resided will be closed for "at least seven days." After that, happy camping! General preventive guidelines still apply, though, as always. (CDC: "Do not pick up or touch dead animals.")
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