In Detroit, 90 percent of rats carry lepto bacteria. Sixty-five percent of Baltimore alley rats are infected, 60 percent of Atlanta rats, and 53 percent of Copenhagen sewer rats.
DeBess studied Portland rats, and found that just 14 percent carried lepto.
Early 20th-century rats brought bubonic plague to almost every major West Coast city. The bacterium first came to North America in 1899, by ship from Hong Kong to San Francisco. An epidemic in the city proper began in 1900, but officials kept it secret to protect business. The outbreak fizzled out in 1904 after 122 died.
The 1906 earthquake that shook San Francisco to ruins provided a healthy environment for the plague bacillus and the fleas and rats that carted it around. A second epidemic began in 1907, this time not a secret. Every port city in the West quaked at the prospect of the Black Death heading their way, and acted to bar the pestilence with quarantines and rat-killing campaigns.
In Portland, Esther Pohl, the city health officer, launched a citywide rapid response. The City Council passed emergency laws to fumigate all ships coming into port, install screens on every building containing food, and pay bounties for rats, which were burned immediately, together with their deadly fleas.
Few other cities moved urgently enough or rigorously enough to keep this little bacterium out. Seattle, for example, moved slowly while the infection took hold. Three people died there, and the plague bacterium escaped into the countryside.
Over a century later, Portland and its environs have never seen a case of plague in humans or any other animals.
Another major influence on Portland's rats, after garbage control, is a tradition of practical collaboration, brought over with the covered wagons on the Oregon Trail and reinforced on the frontier.
Many of the dangers of life in a frontier settlement, such as fire and dysentery, arose from the faults of a few but threatened everyone. Working together to avert those dangers clearly benefited all. From its first years, Portland staged regular cleanup campaigns to keep waterways sewage-free and to clear debris from streets. Settlers of the town, rich and poor, knew from experience their lives depended on the well-being of all their neighbors.
Historian David Alan Johnson, in his book Founding the Far West, finds Oregon's founding ideas—civic duty and the common good—in the situations people left behind when they started out on the Oregon Trail. Most of the emigrants were farmers, ruined by financial volatility in the 1830s and '40s. They wanted nothing to do with rampant self-interest or the panics it produced.
Rat control, then and now, depends on the well-being of other people. Rats reflect human social class, but they do not respect it. The rich family is vulnerable to rats nourished by garbage in the poor family's yard.
Trash collection and enforcement have by no means been consistent or equitable across all neighborhoods for all of Portland's history. But rats there have been kept hungry enough, over the long haul, to suppress population growth.
Citizens anywhere can do what Portland has done—and they can start by helping their neighbors put up rat-proof screens and clean up their yards.