ˁassäwä - essere malarico, di luogo paludoso ecc. che produca la febbre (to be malarial, swampy, etc. get ill with fever)
(TED 1861, Bassano 1918: 684)
bə - in, with, for, by, by means of, by dint of, by means of saying; with, through, in the name of
(TED 1073)
This preposition has the instrumental meaning, while the locative one is expressed through ˀab. Tgr. forms ˀəb/bə- are phonetic variants with no semantic difference.