How long does it take for an infected tick to transmit Lyme disease?
The risk that a deer tick may transmit Lyme disease rises the longer the tick is attached, according to a review by Eisen from the Centers for Disease Control and Prevention (CDC) published in the January 2018 journal Ticks and Tick-borne Diseases. 
According to the report, the probability of a host becoming infected with the Lyme-causing bacteria (Borrelia burgdorferi) appears to increase to approximately 10% after a tick has been attached for 48 hours. The risk jumps to 50% after 63-67 hours, 70% by 72 hours and 90% for a complete feed.
While the tick is attached, the spirochete have time to multiply in the gut, escape into the hemocoel and invade and multiply in the salivary glands before transmitting the Lyme bacteria.
The minimum time to transmit Lyme disease has “generated lively debate in the United States,” writes Eisen. “This topic has been addressed in case studies and letters in response to case studies.”
While some mouse studies suggest that a single nymphal tick bite cannot transmit Lyme disease in less than 24 hours, others dispute this finding. Eisen states, “the possibility that transmission of Lyme disease spirochetes could occur within 24 hours of nymphal attachment under unusual circumstances should not be discounted.” And data “provide a strong justification” for ongoing campaigns promoting Lyme disease prevention efforts, such as tick checks and prompt removal of ticks.
Not all ticks can be considered the same, however. Some ticks that have bitten a host may have already fed on a previous host. This, in turn, can increase the risk of transmission of B. burgdorferi spirochetes. “Partially fed ticks able to re-attach could result from detachment from dead animals or possibly by host grooming,” writes Eisen.
Researchers have shown that infected I. scapularis nymph ticks which had been previously attached to a host for 24–48 hours, then removed and placed onto a new host, can effectively transmit B. burgdorferi spirochete within 24 hours of their re-attachment, explains Eisen.
Transmitting other tick-borne diseases
Deer ticks can transmit other diseases, as well. In fact, studies have found that ticks can harbor up to a dozen different types of bacteria. And, some of these pathogens can be transmitted in less than 24 hours. “Experimental studies have shown that Powassan virus can be transmitted within 15 minutes of tick attachment and both A. phagocytophilum and B. miyamotoi within the first 24 hours of attachment,” writes Eisen.The longer a tick is attached, the greater risk of transmitting Lyme disease. Click To Tweet
But there are pitfalls in relying on tick attachment time to determine your risk of infection. “Bites by I. scapularis nymphs often go entirely undetected and tick-bite victims typically underestimate how long a nymph was attached before it was detected and removed,” writes Eisen. One study found that people “consistently underestimate the actual time the tick was attached prior to being discovered.”
Furthermore, individuals are unaware if they have been bitten by a partly fed tick. If so, their chances of becoming infected increases. And does the infected tick harbor more than just the Lyme bacteria? Is it carrying other tick-borne pathogens? If so, one of these “co-infections” could be transmitted quicker than expected.
- Eisen L. Pathogen transmission in relation to duration of attachment by Ixodes scapularis ticks. Ticks Tick Borne Dis. 2018.
- Piesman J, Maupin GO, Campos EG, Happ CM. Duration of adult female Ixodes dammini attachment and transmission of Borrelia burgdorferi, with description of a needle aspiration isolation method. J Infect Dis. 1991;163(4):895-897.
- Shih CM, Spielman A. Accelerated transmission of Lyme disease spirochetes by partially fed vector ticks. J Clin Microbiol. 1993;31(11):2878-2881.