Human Plague Cases in U.S. Increase in 2006

The Centers for Disease Control (CDC) reports a total of 13 human plague cases in 2006 among residents of four states: New Mexico (seven cases), Colorado (three cases), California (two cases), and Texas (one case). This is the largest number of cases reported in a single year in the United States since 1994.

Dates of illness onset ranged from February 16 to August 14; two (15%) cases were fatal. The median age of patients was 43 years (range: 13--79 years); eight (62%) patients were female. Five (38%) patients had primary septicemic plague, and the remaining eight (62%) had bubonic plague.

The natural reservoir of plague in the U.S. is wild rodents, such as this prairie dog.

Photo from CDC

Plague is a zoonotic disease caused by the bacterium, Yersinia pestis. The natural reservoir of plague is wild rodents.

Human infection usually is acquired through the bites of infected rodent fleas and has an incubation period of 1--6 days (1). Plague also can be contracted from handling infected animals, especially rodents, lagomorphs (e.g., rabbits or hares), and domestic cats, or through close contact with patients with pneumonic plague (however, person-to-person transmission is extremely rare; the last such transmission in the United States was reported in 1925).

During 1990--2005, a total of 107 cases of plague were reported in the United States (CDC, unpublished data, 2006), a median of seven cases per year. The increased plague activity in 2006 is consistent with the predicted relationship between climate and the frequency of human plague in the southwestern United States. Two consecutive February-March periods with high precipitation and an intervening cool summer predicts increased cases of plague the next summer; this effect is thought to lead to increased reproduction and survival rates among rodents and fleas (2).

You can see the full CDC report by clicking on this CDC link, Human Plague --- Four States, 2006