I have not heard of any reverse zoonoses in regards to reptiles-- diseases that humans can pass on to reptiles. However, there are several diseases that humans can pass on to other animals. Our cold sores herpes virus is fatal to old world primates. (Similarily, a rare virus in macaques called Herpes B virus that sometimes causes cold sores in macaques is fatal to humans)

There are several zoonotic diseases that reptiles can give to humans-- salmonella seems to be the main one, but there are a few other out there. http://www.virology.ws/2009/04/08/reverse-zoonoses-human-viruses-that-infect-other-animals/   I would imagine it might be possible for a human with a salmonella infection to pass it on to reptiles, but generally salmonella is carried by reptiles but not actively making them sick. 

Googling reverse zoonosis or anthroponosis and reptiles doesn't come up with too much; looks like humans' raw sewage has given a disease to elkhorn coral and causing a major problem in Carribean. Tuberculosis is also a reverse zoonosis however I don't know if reptiles can get tuberculosis... mainly primates and other mammals. 

I would not be concerned about giving your reptile a cold but I also wouldn't sneeze on your snakes when you're sick, or wipe your snot on them or something... It might just be common sense not to do that as well. 

Oh man I shouldnt have  tounge Kissed that  macaque !!

Lauren (tmth) gave you a well researched, very informed answer. Increase the points to 250 and give them all to her. The question is worth more than 50 points, but her answer is worth more than 250...imho.

That's not really a silly question... we hear about "avian flu" and other illnesses that jump species.  To my knowledge though, there has never been a single documented case of humans directly transmitting a disease to a reptile. 

And hi from Littleton :-)

@Big Sarge I completely agree that Lauren tmth gave a solid answer.  Thank you Lauren for all the details, I love learning new things!  Is it possible to increase the points value after you have posted a question?  I can't find the option to do that.

I agree completely with Lauren's research, and getting best answer :)  Just an aside thought to reptiles acquiring a disease from other animals.  I've read allot into this recently, there is some evidence over the past few years, that what is called Emerald Regurgitation Syndrome (ERS), common in wild caught emerald tree boas, comes from a bacteria that they get in holding facilities that also contain wild birds for export, and comes from the birds themselves.  And apparently, only effects the emeralds.  There are normally amazon tree boas at most of these places, and they are not affected.  While not from humans, I just found this information interesting...

http://www.coralluscaninus.info/EVS_CorallusCaninus.pdf

http://www.redtailboa.net/forums/arboreal-boids/57935-very-interesting-find-emerald-tree-boa-regurge-syndrome-must-read.html