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. 2  Meningitis is inflammation of the membranes (called meninges) that surround the brain and spinal cord.  Both encephalitis and meningitis can be caused by bacteria or viruses, and rarely a fungus, or be noninfectious.
Meningitis and encephalitis are inflammatory diseases of the membranes that surround the brain and spinal cord and are caused by bacterial or viral infections. Viral meningitis is sometimes called aseptic meningitis to indicate it is not the result of bacterial infection and cannot be treated with antibiotics.