Giardia is a concern, as is Lyme disease. A vet should have vaccines for both. You'll also want to ensure that your dog is treated with a flea and tick repellent. Some dogs will need special equipment, such as dog booties to protect the feet. Shorthaired dogs may need a coat or rain jacket for cool, wet weather, but most breeds do just fine.
Heat is a bigger concern.
More than once I've seen hikers on the popular Snow Lake trail, near Snoqualmie Pass in Washington, carrying out dogs that had caved in due to heat. Watch for excessive panting, or whether your dog seems lethargic on a warm day. If so, get the dog in the shade and wet down his coat. You should also take a first aid kit for the dog, with bandages, antibiotic cream, a flea comb, and tweezers for removing ticks. Give the dog a thorough exam each evening, looking for cuts and scrapes he may have picked up as well as parasites.