HARD SCIENCE ON LYME: Ticks can transmit infection the first day
A new article has resurrected the old myth about disease transmission being impossible before a certain time after the tick bites. In the New Haven (CT) Register this week, Dr. David Katz writes: “Ticks need to be embedded for 24 hours or more to transmit Lyme.” This is an improvement on the usual 36-48-hour minimum we usually see, but it is still misleading. See the science and judge for yourself.
By Phyllis Mervine
The CDC claims on their website: “In most cases, the tick must be attached for 36-48 hours or more before the Lyme disease bacterium can be transmitted.” Dr. Katz says 24 hours are enough. What does the science say?
Nymphal ticks are implicated in most human cases of Lyme disease. (Clover 1995) Promptly and properly removing embedded ticks is key to preventing transmission of disease agents. In one study, experimentally infected Ixodes pacificus nymphs do not EFFICIENTLY [emphasis added] transmit Borrelia burgdorferi (Bb) to mice until ticks have been attached for 3-4 days, HOWEVER 11% of mice became infected after only 2 days of tick attachment (<=48hrs.) (Peavy 1995)
Matuschka and Spielman reported that about 5% of infected Ixodes dammini (i.e. scapularis) nymphs transmit Bb in the first day (24hr), about 50% after 2 days. (Matuschka 1995) J. Piesman et al. reported that Ixodes ticks transmitted Lyme disease to 1 of 14 rodents exposed for 24 hours, 5 of 14 rodents exposed for 48 hours, and 13 of 14 rodents exposed for 72 or more hours. The authors concluded that prompt removal of ticks is important.(1987)
Patmas and Remora reported on a case of Lyme disease that was transmitted after only 6 hours of attachment by a deer tick. The authors concluded that, “The current recommendation against treatment of shortduration tick bites may need reconsideration.”(1994)
It is impossible to remove a tick promptly if one does not even know it is there. According to some experts, only 14-32 % of patients who have Lyme disease recall a tick bite. (Nadelman, 2002) Durland Fish, associate professor in the Department of Epidemiology and Public Health at Yale University, wrote this letter to the New York Times (6-14-01):
You report on a new study showing that Lyme disease is very difficult to catch, even from a deer tick in a Lyme-infested area (front page, June 13). But the 3 percent chance of getting Lyme disease from a tick bite cited in the New England Journal of Medicine article that I co- authored pertains only to people who have found and removed a tick, which greatly decreases the chance of infection. Most people never notice the tick that gave them Lyme disease [emphasis added]. About 25 to 30 percent of nymph-stage deer ticks in the Northeast are naturally infected with the Lyme disease bacterium. Nearly all of these infected ticks will cause Lyme disease if they are not removed [emphasis added]. Ticks in this stage are about the size of a poppy seed, making them very difficult to find. People who live in Lyme disease areas should take the risk of tick bites seriously and do all they can to prevent them, keeping in mind the 25 percent chance of infection if they miss a tick, instead of the 3 percent chance if they find one.
UC Berkeley entomologist Robert Lane reports that one of his team of researchers was fed upon by infected nymphal ticks for at least 1-2 days after exposure to tick-infested habitat, despite “extreme personal preventive measures.” He advises people who work or recreate in endemic areas to check themselves frequently and carefully for several days following exposure, since unfed nymphs are very difficult to spot and may be easier to detect when partially replete.(Lane 2004)
Maybe the CDC claim “in most cases, ” turns on the word “most.” But is it really smart to discount those first 35 hours so emphatically when so much is at stake?
To read Dr. David Katz’s otherwise good article, click here.
Phyllis Mervine is the founder and president of LymeDisease.org, as well as Editor-in-chief of The Lyme Times. Contact her at firstname.lastname@example.org.