The World Health Organisation (WHO) says an outbreak of the plague has killed at least 40 people in Madagascar since late August.
So far two cases and one death have been recorded in the capital Antananarivo but the WHO warned those figures could climb quickly due the city’s high population density and the weakness of the healthcare system.
The WHO said the bacterial disease is “one of the most deadly infectious diseases” and can kill people within 24 hours.
It also warned the situation is further complicated by the high level of resistance to deltamethrin, an insecticide used to control fleas, that has been observed in Madagascar.
But the WHO said it would not recommend any trade or travel restrictions based on the information available about the outbreak.
The disease is spread mainly from one rodent to another by fleas.
Humans bitten by an infected flea usually develop a bubonic form of plague, which swells the lymph node and can be treated with antibiotics.
If the bacteria reach the lungs, the patient develops pneumonia (pneumonic plague), which is transmissible from person to person through infected droplets spread by coughing.
The last previously known outbreak of the plague was in Peru in August 2010, according to the WHO.