2 deadly dengue strains behind spurt in city-wide infection

Mumbai: Two worrying strains of dengue have been found to be circulating in Mumbai's air, and could well explain the viral infection's rise and spread this monsoon. Preliminary investigations by the National Institute of Virology, Pune, have revealed that the strains—DEN-2 and 3—have been behind dengue in the city. 

    Mumbai, much like the rest of the country, has been reeling under a dengue spell that peaked between September and October, and is likely to linger for some more time. Virologists, though not completely surprised about the presence of DEN-2, are worried about its predominance. A 2011 study at Kasturba Hospital's molecular lab had found DEN-2 responsible for 85% and DEN-3 for 11% of the cases. 
    Dr Jayanti Shastri, head of microbiology at BYL Nair Hospital, said DEN-2 is associated with more severity world over; more so in south-east Asia. 
    Quoting a recent study that mapped the complete genome sequence and evolution of DEN-2 virus, Shastri said, "There are two major genotypes of DEN-2—American and cosmopolitan—in India, and significant variations have been seen in the cosmopolitan type. These variations themselves could be responsible for the change in the virus' behaviour." 
    Shastri, also head of BMC's molecular lab, said research carried out by Gwalior's Research and Development Establishment, had found the newer Indian DENV-2 isolates were 9% divergent from the older Indian strain. Traces of DEN-2 are found in cities reporting an epidemic-like situation. 
    On the other hand, the NIV also observed that DEN-3 is reemerging as a dominant serotype and that it belongs to the genotype associated with DHF in the subcontinent. "DEN-2 particularly, and in certain cases DEN-3, is capable of causing bleeding, hypotension, liver failure, cardiac condition and shock syndrome, among other life-threatening conditions," said a doctor from Sion Hospital. 
    All dengue strains are capable of causing mild to severe infection. "But infection with one type is not worrisome. It is only when a person gets infected twice with different serotypes that it becomes tricky," said Gautam Bhansali, consultant physician, Bombay Hospital. 
    Officials from the nodal laboratory in Pune confirmed the findings have been conveyed to the BMC. Civic health officials, though, remained tight-lipped. Around 101 samples from Mumbai have been sent to the NIV for serotype testing, a few of which have arrived.