The pure white version of whited bellies is an ALC trait and the genes responsible can be looked upon as a collection of pieces in a jigsaw puzzle. When ALC to ALC is bred the pieces match up and align and the tummy is white. When ALC is bred to a domestic the whited pieces are all mixed up with non whited pieces, some align some don't. The pure whited belly is often lost, as each time the generation is mated to a domestic it introduces even more non-whited genes, that ruin the whited "puzzle". One of the many downsides to having sterile early generation males.
Of course in the Bengal breed then selective breeding takes over and breeding skill comes in. The goal is to match up all those pieces so cats with whited expression ie whitish or greyish underbelllies are mated with others who also have whited expression or who have whited parents in order to put all those ALC pieces back together again in the domestic Bengal cat.
Ringworm as an infection can cause scarring and damage to the hair follicles. Some damage is repairable and the hair loss is temporary whilst other damage is severe resulting in permanent hair loss.
Inbreeding can definitely alter immune function and as the product of a 1/2 brother/sister mating she will have a high inbreeding coefficient, but ringworm can be highly contagious and can need prolonged therapy in any cat or human.
See
http://www.fabcats.org/owners/skin/ringworm.html