There is such a thing as lab-raised clean mosquitoes. I doubt Bill is dumb enough to have had some shipped over from Congo.
My wife is allergic to mosquitoes. I am not sure there is a “safe” mosquito.
http://allergies.about.com/od/insectallergies/a/mosquitoallergy.htm
They probably were clean samples, however this was a horribly negligent and incredibly arrogant stunt by Gates. He may have made his point, but a public apology should be the minimum repentance, if not some sort of gift to those who feel they were unfairly treated. I'm hardly one that sympathizes with those who instantly scream "victim", but this was pretty outrageous, unnecessary, and unacceptable.