Sforno on Numbers 14:37/ספורנו על במדבר י״ד:ל״ז

1וימותו האנשים מוציאי דבת הארץ רעה במגפה, from the type of pestilence which they claimed had caused the death of the people they had seen dying in the land of Canaan during their tour of exploration. (13,32) It was the kind of pollution in the air which kills almost instantly.