An outbreak of Zika virus in western India in the metropolis of Pune in the monsoon of 2024.

BACKGROUND

Sporadic cases and rare outbreaks of Zika Virus (ZIKV) have been reported in India since 2016. Between June to early September 2024; the city of Pune in western India was affected with a large outbreak of ZIKV. Here we report the analysis of epidemiological; clinical and genomic characteristics of the outbreak.

METHODS

Suspected ZIKV cases and pregnant women within 3 km radius of ZIKV positive cases and household contacts were included in the study. The study area included parts of the Pune metropolitan region. ZIKV RNA in serum and urine samples was detected by a single-plex Realtime RT-PCR assay. Representative samples were characterized by whole-genome sequencing.

RESULTS

Among clinically suspected ZIKV cases 63/433 (14.55 %); and 45/1615 (2.78 %) pregnant women surveyed; were found positive for acute ZIKV infection. Majority of positive cases were asymptomatic or had mild symptoms. Two cases reported complications of pyelonephritis and encephalitis respectively. There was no evidence of microcephaly in the fetuses of the pregnant women surveyed. The ZIKV strains were found to belong to the Asian lineage and clustered close to the Rajasthan strain reported previously in India. Mutation linked with microcephaly was not found in these sequences. Follow-up of pregnant women till October 2024 indicated 22 % (10/45) of women delivered healthy babies.

CONCLUSION

The ZIKV strain associated with the present outbreak did not have mutations linked with microcephaly; but had mutations linked with enhanced transmission. Symptoms such as thrombocytopenia; bleeding manifestations; retro-orbital-pain; in a small subset of patients were unique; which were not reported in previous outbreaks in India. The findings highlight the urgent need for enhanced surveillance to plan strategies for public health measures to control the disease spread. Study highlights the need for monitoring the mutations and follow up of ZIKV infected pregnant women and their children to confirm absence of congenital anomalies.