Arbovirus encephalit. The majority of human infections are asymptomatic or may result in a nonspecific flu-like syndrome. Onset may be insidious or sudden with fever, headache, myalgias, malaise and occasionally prostration. Infection may, however, lead to encephalitis, with a fatal outcome or permanent neurologic sequelae. Fortunately, only a small proportion of infected persons progress to frank encephalitis.Cdc.Gov.
4-18 days after bite. Signs generally are seen about 4-18 days after the tick bite. http://www.maine.gov/dhhs/mecdc/infectious-disease/epi/vector-borne/powassan/documents/faq.pdf.