Yes, MYIASES is a Scrabble word!

Letter values in Scrabble US: M 3, Y 4, I 1, A 1, S 1, E 1, S 1.

Is it a valid word?

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

infestation of the body by the larvae of flies (usually through a wound or other opening) or any disease resulting from such infestation