The introduction of the bubonic plague, or black death, nearly wiped out our native ground squirrel populations in San Francisco, and the greater Bay Area. The bubonic plague was introduced to California (and beyond) from ships arriving in San Francisco by way of Hawaii, and China. Y. pestis proved to be fatal to our native ground squirrel populations, as they had no immunity to it. It took a very long time for the ground squirrel population to bounce back from the disease.
The plague was initially introduced to San Francisco via rats jumping Chinese ships. Probably several times. People knew the plague was spread by rats, but they didn’t know of the symbiotic connection with fleas until much later. There are several vector dates (the first, possibly as early as 1855) 1894-1899; 1900-1904; unfortunately California Governor Gage, like tRump, was in full denial.
The 1906 fire burned Chinatown, and eradicated the epicenter, but by then, it had spread by not just rats, but via ground squirrels, there was a species transference, and because Gage was in full denial (not to mention being a racist), there was another larger outbreak in 1907. But that wasn’t the last introduction of Y. pestis to California. The last urban plague epidemic was in Los Angeles 1924-1925.
“the California ground squirrel was identified as a vector of the disease. The initial denial of the 1900 infection allowed the pathogen to gain its first toehold in America, from which it spread sporadically to other states in the form of sylvatic plague (rural plague). However, it is possible that the ground squirrel infection predated 1900.” —Wiki
Any rodent that has rodent fleas can carry the plague—rock (ground) squirrels, wood rats, ground squirrels, prairie dogs, chipmunks, mice, voles, and rabbits. And it seems to have spread to other species families. The marmot or gerbil were probably the original vector species.
I remember when there were bubonic plague warnings at Fallen Leaf Lake during the early 1970s, and the few rare human cases have always been linked to camping and rodents. Just don’t sit near a ground squirrel burrow, or any rodent den, as fleas carry Y. pestis. We were camping at Fallen Leaf Lake, and I was worried, checking for flea bites among the myriad mosquito bites, and later checking my armpits for swelling for weeks as I had caught a vole lumbering down the road and I popped it into a shoebox so I could draw it before releasing it somewhere safer than the middle of the road.
Someone at Lake Tahoe caught the plague this August, but the disease is easily treatable with antibiotics—as long as you know what it is. But it’s pretty rare, the last known case was 5 years ago. Y. pestis outbreaks seem to cycle every few years. There seems to be an El Niño connection, with a 15-year cycle following a warm, moist winter.) California has few human plague victims, but Arizona and the Rockies are hotspots.
Once the plague had leaped from the rats, to native rodent species, it was renamed as sylvatic plague, which has taken a couple of centuries to reach the Rockies via native wildlife corridors. It’s currently affecting black-tailed prairie dog colonies—with a 100% mortality rate, wiping out entire prairie dog towns. An oral vaccine was administered in 2003 (via peanut butter!) to try and stave off the ravages of Y. pestis as an endangered apex species, the endangered black-footed ferret population which fed exclusively on a keystone species, prairie dogs, was also affected. As in starving to death. In an odd turn of events, scientists had to save the prairie dogs from the plague in order to save the ferrets.
The California ground squirrel was identified as harboring the disease during several historic outbreaks. It was the vector that transmitted the disease to other native rodent species. Y. pestis thrives in the mountains, probably introduced by the miners, but rest assured, the disease is no longer a major concern along the coast. But the ground squirrels were completely wiped out in the greater Bay Area—it took them a long time to recover.