John Tull didn’t know he was the heir to a century-old legacy. In 2002, he and his wife boarded a plane from their Santa Fe, New Mexico home and flew to New York City. Shortly after arrival, Tull and his wife both felt ill, with high fevers and odd swellings. In the post-9/11 aftermath, terrorism was feared—the couple was diagnosed with bubonic plague.

But the plague bacterium, Yersinia pestis, hadn’t come from any human with sinister motives—it had come from a rodent (likely a pack rat or a prairie dog) infected in their native state, via a long line of rodents dating back to turn-of-the-century San Francisco.

It’s not conclusively known how Y. pestis first entered the City by the Bay. Plague had broken out in several ports in 1899: Hong Kong, Honolulu, Tokyo, and Sydney; and Marine Hospital Service personnel (the precursor to the National Institutes of Health, led by Dr. Joseph Kinyoun) were kept busy inspecting passengers on potentially infected ships.

Speculation has focused on a steamer called the Australia, which arrived from plague-ridden Honolulu on January 2, 1900. Though the passengers appeared to be healthy, leaving Kinyoun no choice but to allow the Australia to dock, no one can be sure if the ship’s four-legged inhabitants were harboring the deadly bacterium, and subsequently spread it amongst their San Francisco kin. Reports surfaced of an abundance of dead and dying rats in the early months of 1900, but as the epidemiology of plague was still not well-understood at that time, none were tested for the bacillus. The role of rats and their fleas in transmission of plague would not be confirmed until 1905.

Regardless of its origin, plague officially hit the city on March 6, 1900, with the death of a Chinese immigrant named Wong Chut King. King had been suffering from high fevers, and his lymph nodes were horribly swollen and tender to the touch. Delirious, he entered a coma as his organs shut down from the bacterium’s toxins, and died shortly thereafter. Before bacterial cultures were even confirmed, police descended on Chinatown, removing any white inhabitants and sealing off the borders—Chinatown was quarantined, beginning an eight-year struggle that pitted whites against Chinese, scientists against politicians, and state versus federal government.

Because rats and their fleas were the key to disease transmission, the quarantine of Chinatown was not only ineffective, but it also served to sow seeds of fear in the population that was most at risk of plague infection—the Chinese immigrants, packed in to poorly constructed homes permeable to vermin, and unlikely to visit Western doctors when they were ill. Quarantine was lifted after three days had passed with no new reported plague cases, but the damage had been done. Chinatown’s inhabitants mistrusted the city’s public health board, and newspapers published stories claiming that the reported case had been a false alarm. New cases were purposely hidden from the white doctors and health boards.

The deaths, and fighting, continued for years. Travel bans were briefly imposed on Chinese and Japanese immigrants trying to leave the city, and quarantine of Chinatown was attempted once again in late May of 1900, zig-zagging through the city to avoid white neighborhoods and businesses. The second quarantine was a failure as well, and lifted via judicial order two weeks later. Many San Franciscans called for Chinatown to be burned, even while newspapers were actively denying any plague existed within city limits.

When quarantine failed, a desperate Kinyoun ordered ships and trains to deny passage to anyone without a signed health certificate, and requested that detention camps be built to hold the city’s Asian population. Businesses owners howled with rage at the damage they felt Kinyoun was doing to their livelihoods, and accused him of spiking corpses with his own stores of plague bacteria. Soon, even California’s governor, Henry T. Gage, would accuse Kinyoun of this malfeasance, while the state’s legislature called for Kinyoun to be hanged.

By 1901, all but two of Chinatown’s blocks had documented cases of human plague. Kinyoun, defeated, was replaced first by Joseph White and then Rupert Blue, who both encountered the same atmosphere of political denial and patient suspicion that led to Kinyoun’s ouster.

The tide finally started to turn in 1902. California’s plague denial had become a nationwide embarrassment, and other states had threatened to quarantine the Golden State. By mid-1903, 93 cases of the disease had been officially reported, and the clean-up effort finally began in earnest. Blue worked with the city’s Chinese population, and they slowly began to trust him. Carbolic acid was sprayed into buildings and chlorinated lime sprinkled in houses; rats were trapped and poisoned; ramshackle balcony additions were removed from tiny Chinatown apartments; houses were searched for potential plague cases. By mid-1905, after 121 cases of plague and 113 confirmed deaths, Rupert Blue was hailed as a hero, and the epidemic was declared over. The city could rest easy.

Of course, there is a coda. In the wee hours of April 18, 1906, an earthquake struck. Gas mains broke from the impact, and fires broke out throughout the city, damaging at least 25,000 buildings. Water mains also were destroyed, leaving the fires to burn for 4 days. In the aftermath, many residents were left homeless for extended periods of time.

By 1907, even while rebuilding was ongoing, 40,000 were still residing in shacks. The majority of the city lacked working sewers, and garbage littered the streets. The conditions were perfect for a rat explosion, and a fresh outbreak of plague. Human cases quickly reappeared: one in May of 1907, and then an outbreak of cases in August, which led to the closing of the City and County Hospital: it was overrun with rats.

The city had learned its lesson. Immediately, San Francisco’s mayor contacted President Theodore Roosevelt, requesting assistance. Rupert Blue was sent back to the city he’d cleaned up only two years before. This time, determined to truly eradicate the bacterium (and armed with the newly-published knowledge demonstrating that fleas transmitted plague to humans from their rat hosts), Blue instigated a multi-pronged attack, cleaning up the city to eliminate the rats’ food supply; destroying rat burrows and nesting places, and disinfecting them with lime; adding concrete basements or screenings to places including homes, stables, warehouses, and markets; and disinfecting buildings where infected humans or rats had been found. Blue noted, “this latter measure is not considered as important as rat extermination,” driving home that rat control, rather than quarantine, should be the central measure to end plague outbreaks.

Under Blue’s watch, ten million pieces of rat bait had been set out; 350,000 rats were killed outright, and 154,000 of those tested for plague. Not only did this clean-up end the plague epidemic at 159 cases (per Blue's accounting), but also led to a decrease in many other infectious diseases. The city was given a clean bill of health on Thanksgiving, 1908.

However, plague was not gone. Blue was troubled by some outlier cases that he had seen, such as a case in Oakland and another in Contra Costa County, both far removed from downtown. In August of 1908, Blue’s assistant, William Rucker, investigated the latter, and found not only dead rats but also infected squirrels in the vicinity. Blue wrote Washington that the discovery had caused “considerable apprehension,” due to the fact that squirrels were abundant all over the state and beyond. It was already known in Asia that other rodent species—such as marmots—could host Y. pestis. Perhaps here was America’s version of wildlife plague. Not content with saving San Francisco, Blue wanted to attack the next plague frontier: squirrels. He requested $1.50 per day from the federal government to rent rifles and buy ammunition to kill wild squirrels, but was denied because of sloppy paperwork.

Even if Blue had been granted his request, it’s unlikely that he could have controlled the spread of plague in wildlife. By 1919, an outbreak in Oakland caused 17 deaths. In 1924, Los Angeles was struck, resulting in 37 deaths. Most of the cases in both of these epidemics were pneumonic: the bacteria traveled to the lungs and could then be spread between people, like influenza; and both outbreaks were traced back to squirrels. W.H. Kellogg, Chief of the State Hygienic Laboratory at the time, noted “These endemic foci, constituted as they are of wild rodent infection, are, so far as anyone knows at present, permanent and everlasting.”

Today, wildlife plague has spread from San Francisco all the way to the Kansas border; draw a line from the eastern borders of Montana and Wyoming down to the southern border of Texas, and go all the way west to the Pacific: that’s plague country. Human cases number about 10-20 per year, most of those coming from the “Four Corners” states, where the prairie dog is the main host.

While now treatable with antibiotics, plague still can cause serious illness and even death, particularly if it’s not diagnosed quickly. The reverberations of San Francisco’s plague inaction even threaten the endangered black-footed ferret, which relies on prairie dogs as a main food source. While we can’t know for certain if plague would have become established in the United States if it weren’t for years of denial and scientist-bashing over a century ago, we certainly can see that the same mentality is alive and well today in some corners of our country. Alas, the more things change, the more they stay the same.

Sources and further reading:

Marilyn Chase, 2004. The Barbary Plague: The Black Death in Victorian San Francisco.

Myron Echenberg, 2007. Plague Ports: The Global Urban Impact of Bubonic Plague, 1894-1901.

The Plague in San Francisco. Science. 13:761-5, 1901.

Rupert Blue, 1909. Anti-Plague Measures in San Francisco, California, USA. J. Hyg 9:1-8.

Images: prairie dogs and Rupert Blue, from Wikimedia Commons.