Touching, eating or sniffing foods or other household items that have been contaminated by rats is a primary way Lassa fever is transmitted to humans.

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Eighteen states have been affected in "unprecedented outbreak"

More than 3,000 people who may be at risk are being monitored

Lagos, Nigeria CNN  — 

At least 78 people have been confirmed dead and 353 are infected in an “unprecedented” outbreak of Lassa fever in Nigeria, according to the Nigeria Centre for Disease Control.

A further 766 are suspected to be infected, and 3,126 contacts have been identified and are being monitored.

Lassa fever, an acute viral hemorrhagic illness, is endemic in most of West Africa, especially Nigeria, where it was discovered in 1969. Symptoms can be mild or severe, including hemorrhaging in the gums, eyes or nose.

According to the US Centers for Disease Control and Prevention, the disease is transmitted to humans through contact with food or items contaminated by multimammate rats – or through contact with bodily fluids from an infected person.

On average, Lassa fever is deadly in 1% of all individuals infected, with higher rates of 15% morbidity among people hospitalized with the illness. According to an NCDC report from March 4, the case fatality ratio in the latest outbreak was 23.8%.

Sixteen health workers were infected of whom four died within eight weeks of this outbreak.

The NCDC said the country was facing an “unprecedented outbreak” as the disease has spread to 18 states since it began in January.

The agency said it is working with Médecins Sans Frontières and the Alliance for International Medical Action to manage cases in Ondo, Edo and Anambra states.

Many of the cases were self-managed and not tested at the onset because the illness was thought to be malaria, a disease endemic to Nigeria and whose symptoms mimic Lassa fever, said Dr. Chikwe Ihekweazu, director of the NCDC.

Those with symptoms of fever should “go to a health care facility in order to get a test that will determine the cause of the fever.” before treating Ihekweazu said in a statement.