The World Health Organization (WHO) declared on Thursday that Liberia is now free of the Ebola virus and the outbreak is now officially be considered to be over for the country and all of West Africa.

Liberia joins two other countries - Sierra Leone and Guinea - in being declared Ebola free. Sierra Leone achieved that status on Nov. 7, 2015, and Guinea on Dec. 29, 2015. For a country to be declared Ebola free, 42 days have to pass from the time of the negative Ebola test in the body of the last carrier of the virus. Liberia achieved that status on Thursday, which prompted WHO's announcement, according to The Latin American Herald Tribune.

WHO's Chief of Emergency Risk Management and Humanitarian Response, Rick Brennan, said, "All known chains of transmission have been stopped in West Africa," according to the Tri-County Sun Times. The latest round of the outbreak of the Ebola epidemic started in 2014. In this round, more than 28,000 people were infected, of whom nearly 11,300 died.

One of the challenging aspects of controlling the Ebola virus is that the virus can survive for months - or even years - without the carrier showing any symptoms. This is said to be especially true of the presence of the virus in men, in the semen of whose bodies the virus can remain for long periods of time. Hence, any declaration that the virus has been completely eradicated is a difficult one to make and will need to take into account a large number of variable factors.

The current announcement also comes with two important caveats. The first is that the outbreak could recur anytime, especially in the sensitive West African countries in which it occurred before, according to PopHerald. The second is that the lives of the nearly 17,000 people that were infected - but that survived the infection - will now need to be rebuilt in the face of daunting social stigma issues in their own communities.