Johannesburg — For weeks it was simply called “Disease X.” But a mysterious flu-like illness that killed more than 143 people — mostly women and young children — in the Democratic Republic of the Congo has finally been identified.

“The mystery has finally been solved,” Congo’s health ministry said in a statement on Tuesday. “It is severe malaria in the form of a respiratory disease.”

The health agency said malnutrition in the worst-hit region had weakened the immunity of local people, leaving them more vulnerable to disease. People who contracted malaria showed symptoms including headache, fever, cough and body aches.

Congo’s health minister told reporters the country was on “maximum alert” for the spread of the previously unidentified disease, and health officials told CBS News in early December that the remoteness of the outbreak’s epicenter and lack of diagnosis made it difficult to mount a coordinated response.

At least 592 cases have been reported since Congo’s Ministry of Health first issued an alert on October 29. The Ministry announced that the death rate from this disease is 6.25%. More than half of the recorded deaths were children under the age of five who were severely malnourished when they contracted the disease, according to the World Health Organization.

At a press briefing on December 10, WHO Director-General Tedros Adhanom Ghebreyesus said 10 of 12 samples from patients suffering from the mystery disease tested positive for malaria, but said they were still testing for other diseases at the time.

The Congolese government has sent a rapid intervention team to Kwango province, 435 miles southeast of the capital Kinshasa, consisting of epidemiologists and other medical experts. Their goal was to identify the disease and set an appropriate response. Government officials had earlier warned locals to avoid touching people infected with the disease or the bodies of those who had died.

The Congo has suffered from many disease outbreaks in recent years, including typhus, malaria and anemia. The country also grappled with an outbreak of smallpoxwith more than 47,000 suspected cases and more than 1,000 suspected deaths from the disease, according to the WHO.

Anti-malaria drugs provided by the WHO have been distributed to local health centers in Congo, and WHO officials said more medical supplies were expected to arrive in the country on Wednesday.

It is the rainy season in the Congo, which often sees an increase in malaria cases, and will certainly complicate the treatment of those most at risk.