"Often, of course, malaria exacted a toll on both sides. It pushed English Protestants into Catholic Ireland, setting the stage for the Troubles centuries later. But Oliver Cromwell, the Englishman who conquered Ireland, died of malaria, in 1658, rather than take quinine, the only known treatment, because he associated it with its Catholic discoverers, making him a victim of both parasitosis and sectarianism."
https://www.newyorker.com/magazine/2019/08/05/how-mosquitoes-changed-everything