Molecular Epidemiology of Wild Poliovirus Type 1 and Shift in the Historical Reservoir Areas of Pakistan During 2019-2022.

BACKGROUND

Pakistan is 1 of the 2 countries endemic for wild poliovirus type 1 (WPV1). Active clinical and environmental wastewater surveillance along with laboratory investigation is an integral and primary component of polio eradication strategies. The current study is mainly focused on virological data to understand the current epidemiology of WPV1 in Pakistan during 2019-2022.

METHODS

In total, 141 037 stool specimens from patients reported with acute flaccid paralysis and 3171 wastewater samples were tested for detection of poliovirus using cell culture and polymerase chain reaction (PCR). Phylogenetic analysis of WPV1 was performed using MEGA and Nextstrain.

RESULTS

Poliovirus isolates were classified into 15 distinct genetic clusters with multiple transmission lineages. Spatiotemporal trends indicated a significant decline in the incidence of poliomyelitis, reported in 58 districts in 2019 and just 3 in 2022. The historical reservoirs in Peshawar, Quetta, and Karachi successfully eliminated the indigenous transmission chains of wild poliovirus that had been active there for years.

CONCLUSIONS

Our findings reinforce the evolving epidemiology of poliovirus in Pakistan, which is now confined to south-KP. All historically known reservoirs in Peshawar, Karachi, and Quetta block are now free of poliovirus. Intensified clinical and environmental surveillance should be maintained to eliminate the very few remaining transmission lineages and certify poliovirus eradication by 2026.