An unknown virus showing identical symptoms of dengue and chikungunya has affected a large number of people in the city, leavig virologists flummoxed.
Blood samples examined so far have failed to identify the virus at the National Institute of Virology (NIV), Pune.
A team from the NIV recently visited the city areas, where the disease with the symptom of high fever was reported in the last few days, and took some blood samples to NIV.
"No conclusive evidence has been found in the blood tests about the nature of the virus even as the patients have been showing identical symptoms of either dengue or chikungunya," according to sources in the School of Tropical Medicine.
Though it has been widely believed in the medical circle that the high fever and related complications like acute joint pain are related to vector-borne, it has not been proved by the Institute of cholera and enteric diseases (NICED).
Sources said there was a proposal with the NIV to send the blood samples to the World Health Organisation's (WHO) reference laboratory for final diagnosis.
Of the 25 blood samples taken by the NIV virologists from city areas, only one is that of confirmed chikunguniya, while the real nature of the remaining samples were inconclusive, the sources said.
Although no fatality has been reported, official sources said, it was necessary to pinpoint the virus.
Member (health) in the Mayor-in council of the Kolkata Municipal Corporation Atin Ghosh said though the prevalence is "very poor" and the situation not at all alarming, it was advisable to take paracetamol and adequate quantity of water to combat the fever.
"We also advise good rest for the patients to restore vigour," he said.
Ghosh claimed that the civic body had launched a vigorous drive to destroy mosquito breeding centres through various means.
Meanwhile, environmentalists are of the view that though viral fever attacks are common at this time of the season with the winter about to set in, the real identity of the virus should be ascertained.