The World Health Organization says the magnitude of the Ebola crisis in West Africa is "vastly" underestimated.
This as the death toll from the virus has passed 1,000.
Ebola has infected at least 1,900 people in Nigeria, Guinea, Liberia and Sierra Leone since the outbreak began this year.
Half of the victims have died.
The WHO says the outbreak is "expected to continue for some time," largely because of unreported cases and deaths.
Officials with the United Nations Health Agency say they cannot estimate how many infections were never reported to doctors.
The Ebola virus causes viral hemorrhagic fever and affects multiple organ systems in the body.
It is spread through contact with bodily fluids.
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