The number of people in China infected with a new virus, the coronavirus, is increasing.Reports say this infection has spread from Wuhan to other major cities and abroad and on Wednesday the World Health Organization (WHO) will consider declaring an international public health emergency over the coronavirus - as it did with swine flu and Ebola.Such a declaration, if made, will be seen as an urgent call for a co-ordinated international response.But just what is the coronavirus and what can be done to treat it?The BBC's online health editor, Michelle Roberts, explains.