Detroit has/had a feral dog problem.
Anyplace where many people lose their jobs or where there is a local recession will have a dog problem because people will just release their pets.
In a SHTF situation feral dogs and cats will be a huge problem.
When the do-gooders managed to get rid of all the horse slaughter houses in the USA and it caused horse prices to plummet several years ago many many people released their horses into the "wild". Un-calculable numbers of these horses died slow deaths.