Plague-carrying ground squirrels pose little risk of death to humans
Dr. Claire Panosian Dunavan is an infectious disease specialist and a professor of medicine at the David Geffen School of Medicine. This op-ed ran originally on August 11 in the Los Angeles Daily News.
You've got to admit: they're cute. Minutes ago, this thought hit me anew as another one shot past my window.
California ground squirrels — whether hauling acorns, dancing across lawns, or simply racing down the street — are a goofy, high-octane species that normally make me smile.
Except in 2010, that is. Last month — true to expert forecast (more about that later) — a ground squirrel in the Angeles National Forest tested positive for plague, one of mankind's deadliest blights.
How plague entered SoCal squirrels is a story for another day. For now, suffice it to say, plague routinely simmers in the tribe. Once surveillance unearths a positive, however, things happen. Case in point: one day after the recent find, public health and U.S. Forestry officials promptly closed the Los Alamos campground.
As I write this column, the park north of Pyramid Lake remains shuttered while public health staff continue testing, treating burrows with insecticide, and luring squirrels (with tortilla chips!) into dusting stations.
The logic behind the last practice is simple. After coating themselves with chemicals, the Frito banditos go home and spread more pesticide among their friends and relations. This, in turn, kills fleas which might otherwise transfer Yersinia pestis — the deadly plague bacterium - into new hosts.
Beginning to worry about that bite you picked up on your last hike? Feeling feverish? Have aches?
OK, now for the good news. Despite periodic bursts of plague in Los Angeles County among squirrels and other rodents, since 1979, only four human cases have been diagnosed — none fatal. Plus, as a general rule, foothill fleas prefer animals over people. Our last sufferer never got bitten at all. Back in 2006, she fell ill after handling the carcass of a tainted rabbit from Kern County.
(Fortunately, although plenty sick at the outset, the previously healthy woman recovered quickly thanks to aggressive antibiotics and hospital care.)
But just because Los Angeles County hasn't had recent deaths doesn't mean modern plague can't kill. For proof, I called my ultimate source. Dr. Royce Johnson is a longtime infectious diseases specialist at Kern County Medical Center in Bakersfield. He's seen more human cases than anyone currently practicing in California.
"I still remember four patients vividly," Johnson said when I asked about his earliest encounters. "The first was a Tehachapi resident who fell on hard times and spent a lot of time outdoors. When he finally reached us, he was covered with purple blotches and had florid pneumonia. Within eight hours, he was dead.
"In fact, he was dead when I first saw him," my colleague added. "I just didn't know it yet."
Johnson's next patient, who survived, displayed plague's classic hallmark: a grossly swollen, infected lymph node called a "bubo." She picked up her infection while trailer-camping.
A third man who died of plague pneumonia had worked at a garbage sorting and recycling site. He probably inhaled the virulent germs while handling dead animals.
A final casualty fell ill after his cat suffered a massive abscess; Johnson assumed the owner's infection started with a flea bite. (The cat, on the other hand, could have been bitten by an infected flea or eaten an infected rodent.)
Johnson's last vignette launched me on a new train of thought.
In this year of heightened hazard, could local cats and dogs contract plague, I wondered? To answer this question, I called Dr. Emily Beeler, one of L.A. County's public health veterinarians.
"Sure," she replied. "But cats are classically at greater risk because of their predatory behavior."
To put things in perspective: feline plague is rare around here, but, at the same time, according to Beeler, it can be missed. That's because fevers and abscesses (usually due to fights, not plague) are so common in cats. As a result, it takes a pretty dramatic illness for most vets to order special tests for plague.
The silver lining?
"Routine antibiotics may cure more cats than we know," Beeler said.
The logical next step — if you don't already follow this time-honored advice — is to: 1) faithfully apply anti-flea treatments to pets; 2) leave pets behind when going on rustic picnics and vacations; 3) steer clear of burrows; and 4) never handle sick or dead rodents.
Long pants and insect repellent are also recommended for humans in the wild. Feeding cute little beggars from your knapsack? Don't even think about it.
Back to Otospermophilus beecheyi (OK, I admit I just looked that up — that's California ground squirrels to nonbiologists like you and me). The last word on them goes to Gail Van Gordon, Los Angeles County's chief of vector management. But first I'd like to thank her and her crew. They're the ones (appropriately gloved, garbed and sprayed, of course) on the front lines with the squirrels. And not just at Los Alamos campground, but high-risk spots throughout the County.
Van Gordon wasn't surprised, as it turns out, by 2010's index animal. After this year's heavy rain and prolonged spring, she told me, she and her staff saw "way too many burrows." It's a simple equation we should all remember. More rain equals more food equals more squirrels (possibly) carrying plague
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