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The World Health Organization announced Monday that the number of people infected by Ebola in Sierra Leone, Liberia and Guinea has passed 20,000, with more than 7,842 deaths in the epidemic so far, Reuters reports.

Cumulative case numbers in those three countries, which are the worst affected by West Africa's deadly outbreak, stood at 20,081. More than a third are laboratory-confirmed cases in Sierra Leone, which has become the worst-hit country in the worst outbreak of the disease on record.

The WHO announcement comes as health officials observed a sharp uptick in Ebola cases across West Africa. Authorities in Liberia said Monday that there have been dozens of new Ebola cases erupting along the border with Sierra Leone, NBC News reports. Assistant Health Minister Tolbert Nyenswah stated that the announcement marks "a setback for Liberia, which has seen the number of cases stabilize somewhat after having been the hardest-hit country in West Africa."

Ebola prevention efforts are gaining ground. But the fight against the deadly outbreak is far from over, according to an in-depth analysis by the Los Angeles Times

"In the hardest-hit countries, the effects of the outbreak could be felt for years," writes Alexandra Zavis. "Health care systems have collapsed, schools closed, fields left untended and commerce curtailed. The virus has ripped through families, leaving thousands of orphans, many of whom are stigmatized."

"The international community needs better early warning and rapid response" mechanisms to stay ahead of the next disease outbreak, U.N. Secretary-General Ban Ki-moon told reporters in New York on Monday. He assured them that such a test "is sure to come."