A previously unidentified disease circulating in the Democratic Republic of Congo (DRC) is a severe form of malaria, the country’s health ministry has concluded.

Earlier this month, local authorities said the disease had killed 143 people in the southwestern Kwango province in November. The symptoms of the disease are fever, headache, cough, runny nose and body aches.

“The mystery has finally been solved. It’s a case of severe malaria in the form of a respiratory illness,” the health ministry said in a statement on Tuesday, adding that malnutrition in the area had weakened the local population, leaving them more vulnerable to disease.

The statement also said that 592 cases had been reported since October, with a fatality rate of 6.2%.

Reports of an unknown disease had sparked alarm, and prompted the World Health Organization (WHO) to send a team of investigators to the remote part of the DRC.

However, officials had stressed there were high levels of food insecurity and malnutrition in the area that were likely to exacerbate the impact of known illnesses, including malaria. The WHO also pointed to “low vaccination coverage and very limited access to diagnostics and quality case management”.

Malaria still kills almost 600,000 people a year globally, and 12% of those deaths occur in the DRC.

The provincial health minister, Apollinaire Yumba, told Reuters that anti-malaria medicine provided by the WHO was being distributed in the main hospital and health centres in the Panzi health zone.

A WHO spokesperson said more health kits for moderate and critical cases were due to arrive on Wednesday.

WHO director-general Tedros Adhanom Ghebreyesus said last week that 10 early samples from patients in Congo suffering from a mystery illness had tested positive for malaria, but that he had not ruled out the possibility that they had other concurrent diseases.