Nymphal ticks are implicated in most human cases of Lyme disease. (1)
Promptly and properly removing embedded ticks are 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.) (2)

Matuschka and Spielman reported that about 5% of infected Ixodes
dammini (i.e. I. scapularis) nymphs transmit Bb in the first day
(24hr), about 50% after 2 days. (3)  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. (4) 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 short-duration tick bites may need
reconsideration." (5)

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. (6)  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. 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. 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.(7)

1  Clover JR, Lane RS. Evidence implicating nymphal Ixodes pacificus
(Acari: Ixodidae) in the Epidemiology of Lyme Disease in California. Am
J Trop Med Hyg. 53(3):237-240, 1995.
2  Peavey CR, Lane RS. Transmission of Borrelia burgdorferi by Ixodes
pacificus nymphs and reservoir competence of deer mice (Peromyscus
maniculatus) infected by tick-bite. J Parisitol 1995;81:175-178
3   Matuschka FR, Spielman A. Risk if infection from and treatment of
tick bites. Lancet 1993;342;8870:529-30
4   Piesman, J, et al. Duration of Tick Attachment and Borrelia
Burgdorferi Transmission. J Clin Microbiol. 1987 Mar;25(3):557-8.
5   Patmas, MA, Remora, C. Disseminated Lyme Disease After
Short-Duration Tick Bite. JSTD 1994; 1:77-78
6   Nadelman RB, Wormser GP. Recognition and treatment of erythema
migrans: are we off target?
Ann Intern Med. 2002 Mar 19;136(6):477-9.
7  Lane, RS, et al. Human Behaviors Elevating Exposure to Ixodes
pacificus (Acari: Ixodidae) Nymphs and Their Associated Bacterial
Zoonotic Agents in a Hardwood Forest. J.Med.Entomol.41(2):239D248
(2004)

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Phyllis Mervine, President
California Lyme Disease Association
Affiliate of the Lyme Disease Association, Inc.
PO Box 1423
Ukiah, CA 95482

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