Medical experts with the U.N. World Health Organization are investigating an outbreak of an unknown illness with a high mortality rate in the Democratic Republic of the Congo.

WHO has issued a statement saying it is unclear exactly how many cases or deaths are involved. But it says more than half the people affected are under the age of 10.

The statement listed symptoms that include fever, headache, diarrhea or abdominal pain and vomiting.

An investigation team made up of experts from WHO and the Congolese government have arrived in the central part of the country where the outbreak began. WHO says the cause of the illness is unknown, but the Congolese government has increased hygiene and sanitation efforts as a precaution.

Some information for this report provided by Reuters.