The World Health Organization (WHO) has already marked the end of the latest flare-up of Ebola virus in Sierra Leone but it warned that the West African country along with Liberia and Guinea continue to be at risk of the hemorrhagic virus.

In a statement issued on March 17, the United Nations agency said that 42 days have already passed since the last Ebola patient in Sierra Leone tested negative for the highly fatal virus for the second time. This marks the end of the country's latest flare-up, which brought the number of Ebola-related deaths in Sierra Leone to 3,590.

WHO acknowledged the fast containment of the flare-up and commended efforts made by the government of Sierra Leone and partners that effectively stopped and prevented the virus from spreading out of control again.

The agency, however, pointed out that Sierra Leone, Liberia and Guinea; the three countries that were most badly hit by the epidemic continue to be at risk of Ebola flare ups.

The risk for Ebola flare-ups is largely attributed to the virus persisting for longer periods in some survivors.

Data from clinical observations and tests of Ebola survivors indicate that the virus can persist inside the eyes, amniotic fluid, placenta, central nervous system and breast milk for many months in some individuals who appeared to have recovered from the disease.

Results of one study, for instance, have shown that some male Ebola survivors still produce semen that test positive of Ebola virus RNA for nine months or even longer.

WHO urged affected countries to remain alert and to be ready to respond. It also called for strong surveillance and maintenance of emergency response capacity along with strict observance of hygiene practices both in health facilities and at home.

"Investments made in rapid response teams, surveillance, lab diagnostics, risk communication, infection prevention and control measures and other programs were put to the test and clearly paid off," WHO said.

The agency gave an assurance that it will continue to work with the Sierra Leone government and partners to ensure a health system that can effectively help in preventing, detecting and responding to new outbreaks.