My dog used to eat a mouse sometimes. She would always get worms afterwards. Every time she ate a mouse I used to ask the Universe that she would vomit it back within 20 minutes....if she did -okay....if she didn't, that cost us for a vet visit!! Plus prescription wormers!
Hi. The disease toxoplasmosis and intestinal worms (such as roundworm) are the most likely result of eating a rat. These can be quite serious repercussions, causing diarrhoea, pneumonia, liver disease, or diseases of the nervous system. You should definitely get your dog to a vet for a full examination and blood tests.
You can find out more here:
http://essendonvet.com.au/pet-library/should-you-be-concerned-if-your-pet-eats-a-rat-or-mouse
Tony