Give 1mg of Benadryl per pound such that if your dog weighs 30 pounds, you should give it 30 mg of Benadryl. Talk your veterinarian - while antihistamines are generally safe, there are the potential for side effects particularly if your dog has chronic organ failure (renal failure, liver failure, congestive heart failure, etc.).
1 Encephalitis is inflammation of the brain.  Meningitis is inflammation of the membranes (called meninges) that surround the brain and spinal cord.
Tick-borne encephalitis is inflammation of the brain caused by a virus carried by ticks, which are small, blood-sucking parasites. The virus can be transmitted from an infected tick to humans through a tick bite. Tick-borne encephalitis occurs across a vast area ranging from western Europe to the east coast of Japan.