Sometimes I wonder if among all these vaccines they get, something lies latent until conditions are right to interact in a devistating way, with a virus.
Anything is a possible but it would be a better idea to look for horses when you hear hoofs pounding rather than to look for zebras. A change in environment dry and heavy with sand to one that is more humid would create a increase in mucous. An increase in mucous creates a good environment for growth media for pathogens.