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A staff member from local health department spreads pest-control chemicals to kill mosquitoes and larvae to prevent mosquito-borne diseases in Kolkata, India, on Sep. 2, 2019. (Xinhua/Tumpa Mondal)

A staff member from local health department spreads pest-control chemicals to kill mosquitoes and larvae to prevent mosquito-borne diseases in Kolkata, India, on Sep. 2, 2019. (Xinhua/Tumpa Mondal)