NEW DELHI :Fears that the mysterious coronavirus would prove hard to contain have heightened with scientists being unable to determine how far the deadly disease could spread even as the toll rose to 107 and the infection reached 18 countries.

The total number of cases confirmed by China until Tuesday rose to 4,500, around double the 2,830 reported a day before with 26 new deaths. The virus has spread to Germany, Australia, Cambodia and the US, as well as Indias immediate neighbours Sri Lanka and Nepal. At least 64 confirmed cases have been reported outside mainland China, but most of them have been travel-associated.

The World Health Organization (WHO) said the disease may spread further, but steered clear of declaring it a public health emergency of international concern" given its restrictive nature, as most human-to-human transmission is limited to China.

The global health body estimated the transmissibility of the virus-R0 (reproduction rate) ) to be 1.4 to 2.5, which means that an infected person on average is transmitting the disease to 2-3 people at the current contagion rates.

However, researchers from Imperial College London estimated the rate to be in the range of 1.5-3.5, assuming 40 people were infected by the original source, which remains unknown. At least 4,000 people were infected by 18 January in China, much more than what was actually reported by the Chinese authorities, according to the researchers.

It is highly likely that the human-to-human transmissibility of 2019-nCoV is sufficient to support sustained human transmission unless effective control measures are implemented," said Professor Neil Ferguson, one the co-authors who led the study.

The reproduction number, or R, is the indicator epidemiologists use to measure the transmissibility of a virus based on the average number of new infections generated by each infected person. If R is more than 1, it means the outbreak will sustain itself, unless control measures are introduced to slow transmission. If it is less than 1, new cases decline over time and eventually stop.

There is no information on the transmission dynamics of the virus or its clinical spectrum. What fraction of it is asymptomatic, mild, severe or fatal? What makes the virus pathogenic?" asked professor G. Arunkumar, director, Manipal Institute of Virology.

There is no confirmed answer to how long an infected person takes to show symptoms, which WHO said could range from 2-10 days.

The virus is infectious even during the incubation period. This means a person can infect other people, even before he/she starts showing symptoms, the Chinas National Health Commission said.

As of now, researchers are keeping a close watch on the number of infections each day and how the number varies, with increasing restrictions and containment. In the absence of antiviral drugs or vaccines, the control of the outbreak relies upon early detection and isolation of infected cases.

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Virus spreads to 18 nations amid fears contagion will prove hard to contain - Livemint