An unusually deadly seasonal outbreak of plague has gripped the island nation of Madagascar. As of Friday, 258 have been sickened and 36 have died just since August, according to Madagascar’s Ministry of Public Health.

To try to stifle the spread, the government has forbidden public gatherings, including sporting events, and schools have closed for insecticide treatments that kill plague-spreading fleas. People have swarmed pharmacies, desperately seeking face masks and any antibiotics they can get. The World Health Organization on Friday announced that it has released $1.5 million in emergency funds and delivered nearly 1.2 million antibiotic doses to help combat the outbreak.

Plague, caused by the bacterium Yersinia pestis, is endemic to Madagascar and pops up all year-round. But outbreaks can erupt between September to November, with seasonal shifts in rat and flea populations. Rats, which harbor the bacteria, tend to see their populations plump and peak around harvest times in July and August. A boom in the flea population, which transmits the disease, follows in tandem. But as crops are harvested and the weather cools, the rat population shrinks, and the surging, hungry batch of fleas turns to humans.

The island has been battling the disease since it arrived there on steamboats from India in 1898. (The disease still appears in many countries around the world, including the US, but most epidemics occur in African countries.) Madagascar got a handle on its seasonal outbreaks during the 1950s with the help of antibiotics, insecticides, and better hygiene campaigns. But it lost its grip in the 1990s when it started seeing increases in case counts. In recent years, the country has tallied between 275 and 675 cases annually (PDF).

But this year is different. The disease is spreading not just in rural, agricultural areas; it’s also spreading in cities. As of September 30, the disease had taken hold in 10 cities across the island, including the capital, Antananarivo.

“WHO is concerned that plague could spread further because it is already present in several cities and this is the start of the epidemic season, which usually runs from September to April,” Dr. Charlotte Ndiaye, WHO representative in Madagascar, said in a recent statement.

Twice the fear

It’s also spreading in two different ways—by fleas and by people—which some have dubbed a "double plague." Usually, plague infections arise as bubonic plague, spread by flea bites. In this case—the Black Death scenario—Y. pestis moves from the site of a flea bite on a human to the lymphatic system, taking up residence and inflaming a lymph node. This causes a painful swelling called a bubo, where the infection gets its name. If it’s left untreated, the infection can spread to the blood, causing septicaemic plague, or the lungs, causing pneumonic plague.

Pneumonic plague is the most severe form. It can become a life-threatening situation in just 24 hours and can begin to spread from person to person in droplets, coughed or sneezed.

Most of the people infected in the current outbreak in Madagascar have the pneumonic form.

Authorities suspect that the outbreak kicked off when a 31-year-old man from the coastal city of Tamatave visited the Ankazobe District in the Central Highlands . On August 27, during his visit, he developed what he thought were malaria symptoms. Four days later, he was showing respiratory symptoms while taking a shared, public taxi on the way home. He died during the journey, and his body was prepared for burial—without safety precautions—in the Moramanga District Hospital, which was along the way.

Health officials linked his case to 31 others, four of which resulted in death.

Officials caught on to the outbreak on September 11, and cases have piled up since then. People all over the island are spooked by the deadly and fast-spreading pneumonic version of the disease. Lines of people have been appearing at local pharmacies before dawn. They hope to get a face-mask and/or antibiotics, which are now in short supply and expensive.

Johannes Herinjatovo, a 50-year-old resident of Antananarivo, told the Agence France-Presse on Wednesday that he and his wife were alarmed by the current outbreak. “I'd already visited six [pharmacies] this morning and at each one they told me that they didn't have any more masks,” he said. He again left empty-handed.

Local health authorities have been trying to calm residents, telling them that face masks aren’t necessary and that the plague can be treated.

"Plague is curable if detected in time. Our teams are working to ensure that everyone at risk has access to protection and treatment. The faster we move, the more lives we save," WHO’s Dr. Ndiaye said.