Bubonic plague has killed 47 people in Madagascar, and health officials fear the death toll will only rise. The outbreak–similar to the Black Death that invaded Europe during medieval times–is spreading to the capital, Antananarivo.

The health ministry suspects as many as 138 cases have cropped up since the first of the year. Two are now infected in Antananarivo. One isn’t expected to survive. Health workers are utilizing a pest control campaign throughout areas of the city considered to be slums.

“Two hundred households have been disinfected this month,” Philemon Tafangy, who is the health ministry’s secretary general, said.

Those who have come in contact with people infected with bubonic plague have been put on strong doses of antibiotics in an attempt to squelch further spread of the disease.

Bubonic plague is spread by fleas–coming from rats. Humans can contract the disease if they are bitten by a flea that carries the disease.

Outbreak of bubonic plague in Madagascar has claimed 47 victims http://t.co/9iBhb3xwmQ

— Daily Mail Online (@MailOnline) November 25, 2014

The bubonic form prompts swelling of the lymph node, but can be treated with antibiotics. The pneumonic version, affecting the lungs, can be spread from person to person through coughing and can kill within 24 hours.

The U.N. health agency fears that because Madagascar has a high resistance to insecticides that target fleas, people there are at much greater rusk of contracting the illness.

The last case of bubonic plague in Antananarivo was 10 years ago, but Christophe Rogier of the island’s Institut Pasteur believes this outbreak may be related.

“It is possible that the plague continued to survive in Antananarivo for 10 years without touching humans,” with the virus restricted to its rat population, he said. “Rats are a natural reservoir of the plague, and they also survive the plague.”

Although an outbreak of bubonic plague that has killed 47 people is definitely alarming, there is no reason to panic about it increasing to pandemic proportions. The Black Death is estimated to have killed some 25 million people across Europe in the Middle Ages–long before antibiotics were available.