An outbreak of pneumonic plague in China that killed two men is unlikely to cause the mass fatalities associated with historical outbreaks, according to the World Health Organization, according to Bloomberg.

While the disease can kill 60 percent of its victims if left unchecked, early diagnosis and treatment with generic antibiotics such as streptomycin and tetracycline cuts plague patients’ mortality rate to less than 15 percent, the WHO said on its Web site.

Authorities in northwestern China quarantined the town of Ziketan in Qinghai province after two men died from pneumonic plague, the official Xinhua News Agency reported yesterday. Pneumonic plague is the most serious and least common of three forms of the infectious disease. Plague is caused by the Yersinia pestis bacteria, found mainly in rodents, particularly rats, and in the fleas that feed on them.

“These things do happen sporadically in different countries,” Vivian Tan, a spokeswoman for the WHO in China, said in a telephone interview today. “It’s not something we’re very worried about, but we are keeping an eye on it.”

Pneumonic plague occurs when the bacteria infect the lungs, causing symptoms including fever, headache and weakness, and may lead to potentially fatal cases of pneumonia, according to the U.S. Centers for Disease Control and Prevention. In almost all cases, only the pneumonic form of plague can be passed from person to person.

In 2003, plague sickened 2,118 people in nine countries, killing 182 of them, according to the Geneva-based WHO. Almost 99 percent of the cases and deaths were in Africa.

Historical Deaths

Bubonic plague, which historians and scientists think was responsible for the so-called Black Death which killed 25 million people in Europe during the 1340s, occurs when the bacteria infect a patient’s lymph nodes following a bite from an infected flea, causing painful swelling.

The Black Death was the second of three major plague pandemics in history, according to the WHO. The first, known as Justinian’s plague, started in the 6th century and may have killed about 50 million people in Asia, Africa and Europe. The third began in China in the 19th century before spreading worldwide, the agency said.

The last urban outbreak of plague in the U.S. occurred in Los Angeles during 1924 and 1925, according to the Atlanta-based CDC. Since then, there have been about 10 to 15 cases a year in the U.S., mostly in rural areas, the CDC said on its Web site.