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Plague is spreading in many parts of Madagascar, the World Health Organization reported Friday, and a weak health care system means it may spread farther.

WHO reports 119 cases and 40 deaths from plague, caused by the bacteria Yersinia pestis and spread by fleas. Two of those cases and one death were in Antananarivo, the capital and largest city.

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“There is now a risk of a rapid spread of the disease due to the city’s high population density and the weakness of the healthcare system. The situation is further complicated by the high level of resistance to deltamethrin (an insecticide used to control fleas) that has been observed in the country," WHO said.

Plague is easily treated with antibiotics, but can be highly deadly if left untreated. Most cases are bubonic plague, marked by a swelling on the lymph glands. But WHO said 2 percent of the Madagascar cases are pneumonic plague, which affects the lungs, can kill within 24 hours and can spread person to person.

WHO says Madacascan authorities have begun “effective measures” to control the outbreak. Plague is found around the world, mostly infecting rodents, but even in the U.S. there are a few cases every year.

IN-DEPTH

-- Maggie Fox