According to "Archaic Medical Terms" at:

http://www.paul_smith.doctors.org.uk/ArchaicMedicalTerms.htm

Brain fever is the same as Meningitis or Typhus.

Typhus - Infectious fever characterised by high fever, headache, constipation, bronchitis and rash (due to tiny haemorrhages in the skin). The epidemic or classic form is louse borne (the human louse); the endemic or murine is flea borne. Although murine suggests the mouse, the rat flea is in fact the agent of transmission

Sounds like either of these could be highly contagious.

Joe