Is the Zika virus re-emerging as a distinct genetic lineage in India?

An outbreak of Zika fever occurred in Thiruvananthapuram City, Kerala, India, during 2021. At the request of the Kerala state health administration, we investigated the same, towards proposing requisite containment strategies for the disease outbreak. Epidemiological investigations indicated a clustering pattern of Zika fever cases with the presumed index case from a multi-speciality hospital in the city. Preliminary reports on the same had been already reported elsewhere during 2021. Further, entomological surveys carried out evinced the predominant mosquito species in the city, viz. Aedes albopictus (65.55%), Aedes aegypti (22.0%) and Aedes vittatus (12.0%) were naturally infected with Zika virus (ZIKV), the minimum infection rates being 17.9, 7.8 and 3.6, respectively. Also, trans-ovarian transmission was recorded in both Ae. aegypti and Ae. albopictus. This is the first report on the detection of ZIKV from Ae. albopictus in India. Analysis of phylogenetically informative genes of the ZIKV genome indicated the emergence of a distinct lineage of the Asian strain of virus, with five unique non-synonymous mutations, viz. 'A22T' and 'I160M' (pre-membrane) and 'D348N', 'T470A' and 'V473L' (envelope), that were involved in the outbreak. The altered gene expression pattern and evolutionary implications of these unique mutations remain to be investigated. Genetic analysis of the virus isolates from this and other investigations carried out on sporadic outbreaks of ZIKV in the country subsequently indicated that ZIKV is re-emerging as a distinct genetic lineage in India. These findings and other recent reports on ZIKV outbreaks warrant an urgent need for a systematic countrywide surveillance strategy, towards the prevention/preparedness/containment of a massive outbreak of this emerging neurovirulent arboviral disease.