Stating to one of the West Tek Facility (aka The Glow) holotapes, F.E.V. that was being deveploved there (and later at Mariposa) cannot be air-transmitted, and the subject must be either inuculated or dipped into a vat. The Enclave's F.E.V. is a modified strain, that is engineered to kill all the life and be transmitted by air.
man West tek got direct hit

it vaporized part of base itself, when it exploded it was huge mess, and tons n tons of dust that are always ejected into atmosfere and warm air flows surely contained lot of FEV drops.
Aaand F2 Mariposa mutants and Horrigan's Frankie mutated due to inhalation of FEV fumes when they were doing excavations in Mariposa.
......Increased levels of the FEV virus are present in both the air and soil samples we've taken........from mariposa holodisc
2077
# October 30: A week after the initial blast, a black rain begins to fall. The source of the black rain was the massive amounts of radioactive particle debris (mainly soot) from the nuclear firestorm a week earlier. Plants and animals both go rapidly into extinction
this explains the mutated animals?
radioactive contamiantion always damages and kills animals and plans
i think mutations are ususlly caussed when fetus in mother is taking radiation doses. fetus grows, but grows wrongly, because it grows according to damaged and maybe even somehow recombined blueprint (DNA).