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.
This is especially apparent in meningitis involving neonates. Causes of meningitis, encephalitis, and meningoencephalitis include bacteria, viruses, fungi, protozoa, rickettsia, parasite migrations, chemical agents, and idiopathic or immune-mediated diseases.In ruminants, generally bacterial infections are more common than other causes of meningitis or encephalitis.auses of meningitis, encephalitis, and meningoencephalitis include bacteria, viruses, fungi, protozoa, rickettsia, parasite migrations, chemical agents, and idiopathic or immune-mediated diseases. In ruminants, generally bacterial infections are more common than other causes of meningitis or encephalitis.