The bubonic plague raged across Europe in the Middle Ages and devastated China in the 1800's; however, in the 1900's, it hit California, and it nearly led to a major disaster.

Two scientists, the Japanese Shibasaburo Kitasato and the Swiss Alexandre Yersin, had correctly described the bubonic plague in 1894; nevertheless, people insisted on believing that bad food, open sewers, or wounds caused the plague.

This is sad because in 1894, Dr. Mary Miles, who was working in China, reported the widespread death of rats in plague epidemics; moreover; she suggested that there might be a link.

A few years later, a Japanese doctor named Masanori Ogata went even farther by warning doctors to pay attention to insects like fleas that might jump from dead rat to humans and carry the disease with them; later, Paul Louis Simmond, a French bacteriologist, put all this together and did a little experimenting on his own before publishing a paper in 1898 correctly describing how fleas carried the disease from rats to humans.

Most scientists at the time ridiculed him and said that his experiments had been flawed; moreover, back in San Francisco where a Chinese man died of the plague, no one was even looking at any of this research.

Because the first victim was Chinese, people thought the Chinese had brought the disease; therefore, poured carbolic acid down the sewers in Chinatown.

Unsurprisingly, the acid forced the rats, their fleas, and the bubonic plague the fleas carried out of the sewers; consequently more people in Chinatown started getting sick as the rats and fleas moved into the houses.

As more dead started turning up, the city Board of Health announced they had a problem; meanwhile, the governor was afraid that the other states would stop buying California's fruit and crops and insisted that there wasn't a problem even though dozens of people were sick or dead.

President McKinley himself had to pass rules and regulations allowing health officials to step in, luckily, the number of plague victims tapered off after more than a hundred people died, but no one knew exactly why.

In 1905, a group of British doctors and scientists published a description of the plague that included all of the research done by those earlier scientists; ironically, the doctors in California listened to the English conclusions, even after ignoring the Japanese, Swiss, and French scientists.

Then, in 1906, when a huge earthquake hit San Francisco, leaving people homeless, injured, weak, and vulnerable; in fact, by 1907, the first cases of plague were showing up in a second outbreak, and the city was ready for a major disaster.

However, this time the doctors and the government understood that rats and their fleas posed the real danger; therefore, the government offered a bounty on every rat people could kill.

Homeless and unemployed, many citizens of San Francisco turned to rat-killing for a living; moreover, with a better understanding of how to avoid the fleas and fleabites, a potential disaster was avoided.

While the United States has avoided the major plague epidemics that ran rampant across the other continents, it was a close call, in fact, if scientists had been a little slower, California might have had its own horror stories about the dead being left to rot in the streets, just like Europe and China.