New Delhi: World Health Organisation (WHO) is planning to hold an international scientific meeting in Geneva to review the various developments and analyse the questions surrounding the Severe Acute Respiratory Syndrome (SARS) epidemic, even as the number of people carrying the SARS virus in India went up to seven and the world figure neared 5,000 mark.

The meeting, to be organised during June 17 and 18, would review the epidemiological management and laboratory findings on SARS, WHO said.

Its website said that key participants in the response to the current outbreaks and other public health authorities would be invited to the meeting.

The meeting is likely to throw light on the new disease, which has emerged as a challenge to scientific community. In India, most of the cases have been asymptomatic or have been accompanied with low-grade symptoms, which also raises the question of possibility of transmission by people who do not have symptoms but carry the virus, health experts said.

"The virulence (how badly the virus causes disease) may depend on a number of factors like age of the patient and the viral load," Prof Anoop Misra from the Centre for Human Nutrition, the University of Texas Southwester Medical Centre at Dallas, said.

For example, an elderly person has more chances of contracting any disease than a younger person. "But, since the epidemic is just evolving we do not know more details as yet," he said.

"Whether SARS virus will cause disease in all the persons it infects is not known since not all contacts of the patients have developed disease," Misra said.

Health experts in the government said that mild symptoms may also be due to the fact that the new virus that is causing infection here is second or third generation virus. It may be that virus has already mutated.

They said the disease was new and everything related to it, including the tests, was under evaluation. Usually, corona viruses die in four- six hours outside body, but concrete information in this regard was not available for the new virus.

They said asymptomatic carriers may transmit the disease, as it happens in typhoid and some other viral diseases. Besides, it is also not known whether a patient is infective during the incubation period. In some diseases, people who have mild symptoms prior to the onset of disease do transmit.

Misra said whether the new Corona virus is the cause of the symptoms of SARS cannot be said with certainty. According to the scientific information available so far, a positive test result for SARS means that the patient with this syndrome had infection with the new Corona virus, which "might" be the cause of SARS.

The evidence suggests that this new human Corona virus can cause SARS, but other viruses or combinations of viruses might also be responsible for SARS, he said quoting information with CDC Atlanta. Scientists are now trying to determine with certainty that this Corona virus causes SARS.

Reports said that death rates from the new illness may vary among countries partly because of different strains of the virus. For example, the viral strain in Canada may be more virulent than that causing infection in US.

Similarly, the strain that caused outbreak of SARS in an apartment building in Hong Kong may be different from the one causing illness elsewhere there.

PTI