Cephalitis and Sleepy sickness

Cephalitis noun - Inflammation of the brain usually caused by a virus; symptoms include headache and neck pain and drowsiness and nausea and fever (`phrenitis' is no longer in scientific use).

Sleepy sickness and cephalitis are semantically related. In some cases you can replace phrase "Sleepy sickness" with "Cephalitis", this terms are similar.

Sleepy sickness noun - An encephalitis that was epidemic between 1915 and 1926; symptoms include paralysis of the extrinsic eye muscle and extreme muscular weakness.

Cephalitis and sleepy sickness are semantically related. You can use "Cephalitis" instead a noun phrase "Sleepy sickness".