Standardization of ELISA for anti-chikungunya-IgG antibodies and age-stratified prevalence of anti-chikungunya-IgG antibodies in Pune, India.

Chikungunya (CHIKV) reemerged in India after a gap of 32 years, in 2005-2006 and has established endemicity in Pune. To assess the degree of CHIKV exposure, we estimated age-stratified prevalence of IgG antibodies to CHIKV in Pune population. This retrospective study utilized age-stratified serum samples collected from 15 wards of Pune in 2017 for dengue (DENV) virus study. Indirect anti-CHIKV-IgG ELISA was developed and used to test 1904 samples. Exposure to CHIKV and DENV was compared in the same population. CHIKV-specific plaque reduction neutralization test (PRNT) was employed to evaluate ELISA positivity and neutralizing potential of anti-CHIKV-IgG antibodies. Indirect ELISA showed 98.5% concordance with commercial ELISA. Seropositivity to CHIKV was 46.4%, one-third children < 15 years being antibody positive. A significant increase (45%, p = 0.026-0.038) was noted at 16-25 years and varied between 48 and 56% until the age 65. In elderly (65 + years), antibody positivity was reduced (41%, p = 0.01). In children, CHIKV-PRNT titers increased with age and remained comparable from the age group 11-15 until > 65. Exposure to DENV was higher than CHIKV. Lower exposure of children and elderly could be due to lesser exposure to the vectors. High prevalence of IgG antibodies needs to be addressed while planning vaccine studies for CHIKV.