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.
URL of this page: //medlineplus.gov/ency/article/001415.htm. Encephalitis is irritation and swelling (inflammation) of the brain, most often due to infections. Encephalitis is a rare condition. It occurs more often in the first year of life and decreases with age. The very young and older adults are more likely to have a severe case. Encephalitis is most often caused by a viral infection. Many types of viruses may cause it.