Every day in most towns in Ireland, dogs are reported wandering the streets on their own. This article (behind a paywall) and this short podcast (below) looks into the “lost dog” phenomenon, and discusses how this should be tackled.
10 min podcast and one page article: the Lost Dog phenomenon in Ireland
Please note that I am unable to answer veterinary questions in comments. If you have questions or concerns about your pet's health it is always better to contact your vet.