How long does a tick have to be attached?

Some people ask how long a tick has to be on a human before it's possible for the victim to acquire Lyme disease. 

This from Steve Callister, PhD, Research and Diagnostics Laboratory Director, Gundersen Lutheran Medical Center, Professor at University of Wisconsin-LaCrosse: (personal communication, shared with permission of Dr Callister):

"There is really no definitive data on transmission time to mammals after tick bite.  Years ago, a small research project using rabbits to study transmission resulted in conclusion that it takes atleast 24 hours for any transmission to occur...  Thereafter, press jumped on this and common belief now is it takes at least 24 hours before risk of illness.  However, I totally disagree as we have seen lots of Lyme patients over the years who have become ill even after removing tick within several hours of bite – In fact, I would argue that time of transmission is totally dependent on spirochete load in the tick and genetic susceptibility of the mammal – however, no one has bothered to study this.  Bottom line, no tick bite is risk-free, especially if recipient is susceptible genetically.  Hope this helps. 

-Steve "