Marin/Sonoma Mosquito & Vector Control District
800-231-3236 (toll free)
707-285-2200 (office)
595 Helman Lane, Cotati, CA 94931-9736

PHONE
800-231-3236 (toll free)
707-285-2200 (office)
707-285-2210 (fax)

ADDRESS
595 Helman Lane
Cotati, California
94931-9736

HOURS
Monday through Friday
7:00AM to 3:30PM

6. PLAGUE (BLACK DEATH, BUBONIC PLAGUE)

Plague is caused a bacteria named Yersinia pestis carried by fleas. For eons it lived in the blood of resistant wild rodents in northern Asia. During the Middle Ages, it somehow began to infect the domestic rats that infested towns and cities. After the rats died, their fleas fed upon the villagers themselves. Unable to imagine what was happening to them, more than half of Europe's entire population died as black death swept the continent.

In 1900, infected rats reached California on a ship from Asia. Soon plague spread from the port of San Francisco to other nearby cities, and to deer mice Peromyscus, and other resistant rodents. While towns in Marin and Sonoma counties largely escaped the outbreaks that affected most temperate regions of California, Y. pestis became firmly entrenched in the Coastal and Sierra Nevada Ranges.

Ground squirrel at its burrow entrance; photo by
Barbara Samuelson; Sunol Regional Park, Calif.

Today, plague is endemic in resistent wild rodent populations throughout the western United States. Preditors or scavengers can get the disease when they eat their prey, and hunters when they handle or skin infected game animals. From time to time the bacteria spreads to more susceptible rodents, like ground squirrels Spermophilus beecheyi. Epizootic outbreaks decimate the squirrel colonies, leaving hoards of infected, hungry fleas around the now empty burrows. Sites like these are especially dangerous to hunters, campers and nearby residents.

Public health workers in endemic areas keep a close watch for die-offs in ground squirrel colonies. They sometimes close campgrounds or regional parks as a preventative measure, and apply insecticides to kill the fleas around the abandoned burrow systems.

Internet references:

• "Human Plague - 2006"  - This report from the National Centers for Disease Control details 13 cases (two in California) with two deaths.
• "Anatomy of an Epidemic"  - Find out how Plague and other epidemic diseases start, spread and may be controlled.
• Plague in California, 1994-1995. by K. W. Emery and B. A. Jinadu. in California Morbidity, November 1995.