A mystery illness that has killed at least 13 people in Liberia in recent weeks is linked to meningitis, the country's minister of health has said. Medical samples from the deceased tested positive for Neisseria meningitidis, also known as "meningococcus".

"Based on these initial results from the CDC Atlanta [US Center for Disease Control], we believe that we are dealing with a probable outbreak of meningitis in Sinoe [county] which spread to Montserrado and Grand Bassa counties," Dr Bernice Dahn said on Monday 8 May, according to Reuters.

She called for calm and said the government was considering a mass vaccination programme to tackle the outbreak, which was linked to the attendance of a religious leader's funeral.

Neisseria meningitidis is a highly contagious type of bacteria that affects the brain membrane and spinal cord, according to the World Health Organization (WHO). The disease is fatal in 50% of cases if untreated, and it is transmitted through close and prolonged contact with infected people. Symptoms include stiff neck, high fever, sensitivity to light, headaches and vomiting.

So far, a total of 31 cases have been reported in the West African country.

The illness has hit Liberia ten months after the country was ravaged by a hemorrhagic fever known as Ebola.

Liberia was one of the three West African countries – along with Sierra Leone and Guinea – worst affected by the Ebola outbreak, which began in 2014. At least 11,310 people died and 28,600 were infected.

Nearly 5,000 of the deaths were reported in Liberia. The authorities, however, have ruled out a possible return of Ebola to the country.

WHO declared Liberia Ebola-free in June 2016, officially ending the outbreak in West Africa. Sierra Leone was declared free from the virus in March 2016, while Guinea was given the status in December 2015.