Encephalitis is inflammation of the brain. One of the reasons of encephalitis is parasites migrating to the dog's central nervous system. These parasites may be present within the host affecting another organ system or may be picked up picked up from another host. These then gain entry via blood or through adjacent tissues making their way to the CNS.
Symptoms associated will depend on the type of parasite and portion of CNS affected. For example Cuterebriasis is characterized by the sudden onset of behavior changes, seizures, and vision issues while Angiostrongylus cantonensis may cause lumbosacral syndrome in puppies leading to paralysis of the hindlimbs, tail, and bladder.
Often parasite infections are asymmetrical affecting one side but not the other.