The World Health Organization (WHO) has declared on Tuesday that Guinea was free of Ebola transmission. The Ebola outbreak is over in Guinea for the first time since the virus was detected in the country two years ago.

The Ebola outbreak that emerged in the West African countries began in Guinea in December 2013 and spread to Liberia and Sierra Leone.

According to BBC News, the disease killed more than 2,500 people in the West African state and a further 9,000 in neighbouring Liberia and Sierra Leone. Ebola virus killed more than 11,000 people and sickened more than 28,000 across 10 countries.

Liberia and Sierra Leone were earlier declared Ebola-free by the WHO. Liberia was declared to be free of Ebola transmission in September, and Sierra Leone in November. However, Liberia has had two new cases after the country ended transmission.

The WHO statement said that the declaration was made because two 21 day incubation cycles of the virus have passed since the last person in Guinea confirmed to have Ebola, twice tested negative for the virus, CNN reported.

Guinea now enters a three month period of heightened surveillance as the virus could re-emerge. The surveillance period will make sure that any new cases are identified quickly.

Researchers believe that the first person to become infected with Ebola virus was a 2-year-old boy who lived in Gueckedou town in southern Guinea. The last Ebola patient and survivor in Guinea is the three-week old girl whose mother died of Ebola, according to New York Times.

The last patient received two experimental treatments including the antibody combination Zmapp and an antiviral drug made by the pharmaceutical company Gilead.

Following the declaration, the Guinean government announced plans for a celebration with well-known musicians in Conakry, the capital. Some residents hoped that the declaration would lead them to resume international trade and travel.

However, the WHO said that challenges remain, including the fact that Ebola virus may persist in certain parts of survivors' body such as the testes and breast milk for up to a year. In other cases, how the virus re-emerged to cause illness remains a mystery. Experts warn that Ebola cases may still emerge.

A Guinean health worker and Ebola survivor Alpha Seny Souhmah said that even if open transmission has been stopped, Ebola disease has not been totally defeated.

The WHO's Ebola response team said that the coming months will be critical and the country needs to be sure that they are fully prepared to prevent, detect, and respond to any new cases.