Yes, SCHISTOSOMIASIS is a Scrabble word!

Letter values in Scrabble US: S 1, C 3, H 4, I 1, S 1, T 1, O 1, S 1, O 1, M 3, I 1, A 1, S 1, I 1, S 1.

Is it a valid word?

SCHISTOSOMIASIS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

an infestation with or a resulting infection caused by a parasite of the genus Schistosoma; common in the tropics and Far East; symptoms depend on the part of the body infected