When thinking of the plague, one might conjure images of 14th-century English villagers surrounded by rats and fleas, perhaps dragging swollen corpses out to a cart to the cry of “Bring out your dead!”
One probably doesn’t conjure up serene San Bruno Mountain.
But sure enough, the highly infectious disease has been haunting the mountain for generations.
“There’s plague on San Bruno Mountain. We regularly get mice who test positive there,” said Chindi Peavey, vector ecologist for the San Mateo County Mosquito and Vector Control District.
The plague, which is carried by fleas, mice, rats, squirrels, cats and other animals, famously wiped out about 75 million people in the 14th century, among other epidemics. The bacterial disease causes swollen “bubos” in the underarms and groin. It can be fatal within a few days if not caught early and treated by antibiotics. The pneumonic plague afflicts San Bruno Mountain wild animals and can be transmitted directly through coughing.
The weekend’s 300-acre grass fire and other recent smaller blazes on the 1,314-foot mountain, which is circled by Daly City, Brisbane, Colma and South San Francisco, may have driven infected rodents into residential neighborhoods. But Peavey says that residents should not be alarmed because the risk of transmission of the disease is low.
She did, however, say that if a house cat caught an infected mouse, it can in turn infect its owners. The transmission from cat to owner is the most common way of catching the plague, she said.
Plague in mice, rats and squirrels on San Bruno Mountain was first discovered in the 1940s, when the mountain was home to a host of hog and berry farms, Peavey said. After the discovery, the squirrels were eradicated. But because it’s nearly impossible to eradicate a population of wild mice, those were left alone, she said.
Today, only about five cases of plague occur in California each year, Peavey said.
The San Francisco Peninsula is the site of the nation’s first and largest outbreak of urban plague. An outbreak in 1900 killed 118 people.
Several San Bruno Mountain residents said they were not at all concerned about catching plague. But resident Mike Evanchak, owner of a cat he describes as a “champion mouse and rat catcher,” said the prospect worries him. He said he’s noticed an unusual number of feral cats in his yard since the fire, as well.
“There’s been a lot more squirrels in the last three or four years, too,” he said. “And I know my cat’s out there hunting, so it does concern me.”
By the numbers
» 75 million: People killed worldwide in the 14th-century plague epidemic
» 118: People killed in a plague epidemic in San Francisco in 1900
» 1,000 to 3,000: Cases of plague every year worldwide
» 10 to 15: Cases of plague in the United States each year
» 1 to 5: Cases of plague in California each year
Source: County Mosquito and Vector Control District