This is a lot of two horror novels from the 1970's and 80's, Cujo by Stephen King and The Pack by David Fisher. Cujo is a movie tie-in edition.

From the publisher:

The Pack (1977): In the August heat they frolicked on the beaches, fetched sticks, played with the children. Then the summer dwellers left, abandoning them to the island's harsh winter. Ravenous hunger and violent rage have brought them together under a cunning, ferocious leader. Man has betrayed his best friend--now the dogs will have their day. It's a bitter winter, and the dogs of summer have grown hungry ... and vicious!

Cujo (1982): Cujo is a 200-pound Saint Bernard, the best friend Brett Camber has ever had. One day Cujo chases a rabbit into a cave inhabited by sick bats. What happens to Cujo, how he becomes a horrifying vortex inescapably drawing in all the people around him, makes for one of the most heart-stopping novels Stephen King has ever written.

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