Read-up on it, A. West Nile isn't on the list, but it's only a shortened list...
http://www.birds.cornell.edu/cfw/challenges/bird_diseases.html
Bacteria and germs on the head/hair can be easily transmitted to the hands, then to the eyes, nose, mouth etc. Bird nests are notorious for being improperly-handled and giving humans all kinds of medical problems.
Tweety-Pie Bird is taking a shower at this very moment...
I work in the animal business and am well aware of all the "scary" diseases. However, my point was that birds are no more likely to carry germs than other wild animals. There is no need to panic when one touches you.