DOUALA/N'DJAMENA (Reuters) -A resurgence of tit-for-tat violence between herders and farmers has killed at least 22 people and injured more than 30 others this week in Cameroon's Far North region, a regional government official said on Thursday, prompting residents to flee to Chad. Hundreds of people fleeing the violence between Arab Choa herders and Mousgoum and Massa farmers have streamed across the border into neighbouring Chad, the mayor of Chad's capital N'Djamena, Ali Haroun, told Reuters.