This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 痆 is uncertain. It combines 疒 (sickness) with 尼, but the role of 尼 is unclear.
The sickness enclosure 疒 wraps around 尼, but the overall meaning is unclear. Imagine a rare illness whose name is lost.
For ダツ, picture a doctor dabbing a wound with a cloth: dab -> ダツ, treating the mysterious sickness inside 痆.