Evidence of dengue and chikungunya virus co-infection and circulation of multiple dengue serotypes in a recent Indian outbreak.

In India, dengue endemic areas overlap with chikungunya-affected areas and both the viruses are transmitted by same vector, Aedes aegypti - thereby increasing opportunity of co-infection by both viruses. Present study was carried out to understand the DENV-CHIKV infection dynamics during recent outbreaks in eastern India (West Bengal state) and its implication on disease manifestations. Blood was collected from 326 symptomatic febrile patients. Patients' serum was subjected to serological diagnosis for presence of anti-dengue-IgM, anti-chikungunya-IgM antibodies and dengue-NS1 antigen by ELISA. Viral RNA was extracted, and presence of dengue virus (DENV) and chikungunya virus (CHIKV) genome, their viral load (VL), and serotype among infected patients' plasma was determined by real-time qRT-PCR. Statistical analysis was performed by using EPI INFO software. DENV and CHIKV were detected in 54% and 33% of symptomatic patients respectively, among whom 23% were harboring both viruses. WHO classified warning signs were detected among 64% DENV patients and 61% DENV-CHIKV double-infected patients. Patients with warning signs always had much higher DEN VL than those without warning signs. Hemorrhagic manifestation and abdominal pain was found in significantly higher frequency among patients with high dengue VL (>10,000 copies/ml). DENV2 was the most predominant serotype among monotypic dengue patients, whereas DENV2-DENV4 combination was most prevalent among patients infected with dual dengue serotypes. This study indicated that DENV-CHIKV double infection and high dengue VL contributed towards severe disease manifestations among infected patients. DENV2 and DENV2-DENV4 combination were the most prevalent serotype(s) found in current outbreak.