The World Health Organization has reported that there is a deadly "unknown disease" spreading in one region within the Democratic Republic of Congo.

Local health officials in Congo are partnering with the World Health Organization to investigate.

The phrase "unknown disease" primarily means that the disease has not yet been identified.

In previous cases, the cases are linked to a known disease, but a lack of available testing leads to lack of certainty.

For example, there was a separate report of an "unknown disease" in December of last year in Congo that was later attributed to illnesses from malaria and respiratory illnesses.

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The latest numbers from the WHO's Africa Region show that there are 431 cases linked to the outbreak and 53 deaths since January.

Early investigations traced the outbreak's origin to three kids, all under 5 years old, who developed symptoms after eating a bat carcass.

Symptoms included fever, headache, diarrhea and fatigue - which later progressed to signs associated with hemorrhagic fevers and death.

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Ebola and Marburg have already been ruled out, officials say. Nearly half of deaths occurred within 48 hours after symptoms start.

"The remote location and weak healthcare infrastructure increase the risk of further spread," the WHO notes in its report.