Two reports from laboratories run by the Centre have revealed that all four strains of the dengue virus are active in Calcutta, the finding highlighting once again the lapses in the civic bodys vector-control programme.
The reports by the National Institute of Immunology in Delhi and the Calcutta-based Indian Council of Medical Research are based on a molecular diagnosis of the blood samples of dengue patients.
The government had sent the samples, all from patients in Calcutta, to the two facilities to find out the reason for the virulence of the outbreak that claimed at least 13 lives in the city this year worst since 2005 that saw 12 dengue deaths.
The tests by the National Institute of Immunology have revealed the presence of types 1, 3 and 4, health department spokesperson Asit Biswas told Metro on Sunday.
Sources said the other study, conducted by Shyamalendu Chatterjee of the virus unit of the city institute, detected types 2 and 3. The report will be handed over to the health department soon.
Experts said the presence of all four strains was a pointer to the unchecked growth of mosquitoes while the Calcutta Municipal Corporation ignored early warnings.
The larvae of the dengue-causing Aedes aegypti mosquito were detected as early as May in various parts of the city. Had the civic body conducted proper entomological studies and launched vector-control measures on time, such large-scale spread of dengue could have been prevented, said a health department official.
The civic authorities had been denying for weeks that there was an outbreak and changed its stand only after the chief minister summoned mayor Sovan Chatterjee to Writers Buildings on September 11 and reprimanded him for failing to contain the spread of the disease.
We had no clue that all strains of dengue are active this time, said Chatterjee, promising an effective approach next year.
Apart from the failure of the vector-control drive, experts have cited lack of immunity to most strains of the dengue virus as a reason for the outbreak.
Earlier studies had suggested that type 3 was most dominant. The others were negligible. This could be the reason for the general lack of immunity to the other three strains of the virus, said a virologist in Calcutta.