A WOMAN in Japan has tested positive for the coronavirus twice raising fears that the bug lies dormant.
The 40-year-old was working as a tour guide in the virus epicentre of Wuhan when she was struck down with the illness last month.
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She was discharged a week later when she recovered and tested negative for Covid-19, despite still having a cough.
On February 21, she went back to see her doctor complaining of a sore throat and chest pains.
The woman was tested for the virus for a second time, with officials confirming she had the disease last night.
Health bosses in Osaka confirmed that the bus driver has also tested positive for the virus.
Experts say that it is unlikely the woman would have caught the disease twice, rather she remained "persistently infected".
Prof Mark Harris, a virologist at the University of Leeds, said: “It is unlikely that they would have been reinfected having cleared the virus, as they would most likely have mounted an immune response to the virus that would prevent such reinfection.
"The other possibility therefore is that they did not in fact clear the infection but remained persistently infected.
They would most likely have mounted an immune response to the virus that would prevent such reinfectionProf Mark Harris
"Although coronaviruses generally cause short-term self-limiting infections which are cleared, there is some evidence in the scientific literature for persistent infections of animal coronaviruses (mainly in bats).
"Clearly we need more information about these patients, such as were there underlying medical conditions or a change in circumstances that might have allowed the virus to escape immune control."
Sir Timothy O’Shea, of the University of Edinburgh, said: "Given the number of reported cases thus far, it would seem unlikely that this is a common occurrence, and thus should have only a small impact on the overall epidemic projections themselves."
Prime Minister Shinzo Abe told a task force today that all of Japan's schools will be asked to close from March 2 until their upcoming spring break to contain the virus.
The number of cases in Japan has now risen to more than 200, up from the official tally of 186 late on Wednesday.
This doesn't include the 704 reported from an outbreak on the Diamond Princess cruise liner that was quarantined off Tokyo earlier this month.
On the main northern island of Hokkaido, 13 new cases - including two under the age of 10 - were confirmed, the public broadcaster NHK reported.
Japan toll climbs
A man in his 80s died in Hokkaido after contracting the coronavirus, bringing the total number of people who have died in Japan to eight - including four from the ship.
Though a first known case for Japan, second positive tests have been reported in China - one reported on February 21 - where the disease originated late last year.
Health Minister Katsunobu Kato said in parliament the central government would need to review patient lists and keep tabs on the condition of those previously discharged.
Philip Tierno Jr, Professor of Microbiology and Pathology at NYU School of Medicine, said: "Once you have the infection, it could remain dormant and with minimal symptoms, and then you can get an exacerbation if it finds its way into the lungs."
The government has urged that big gatherings and sports events be scrapped or curtailed for two weeks to contain the virus while pledging that the 2020 Summer Olympics will go ahead in the capital Tokyo.
Japan has changed its strategy in combating the contagion, seeking to slow its spread and minimise the number of deaths.
The health ministry said on Thursday that with the Diamond Princess still located south of Tokyo, about 240 foreign and Japanese crew members who have tested negative for the virus would disembark from the ship over the next few days.
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Those with no symptoms would remain at a facility near Tokyo for further monitoring, the ministry said in a statement.
An official could not immediately confirm the total number of crew on board the ship.
The outbreak has spread rapidly and widely, infecting about 80,000 people globally and killing nearly 2,800, the vast majority in mainland China.