TickEncounter frequently hears many varying statements about the time it takes a tick to transmit a tickborne infection after biting a host. We and others have conducted several carefully controlled experiments -- all with similar outcomes -- to evaluate the concept of pathogen transmission delays in blacklegged ticks. We stand behind the statement that it generally takes longer than 24 hrs of attachment before blacklegged ticks can transmit an infectious dose of the Lyme disease and human babesiosis agents. We realize that people -- even other scientists -- sometimes have different experiences or they interpret experimental data differently. It is our goal to help translate science into information that can be used -- in this case to best prevent tickborne disease. To this end, below we're providing access to the existing peer-reviewed published research on this topic (PDF downloads available below). We keep an open mind to reviewing empirical evidence and we welcome readers to send other peer-reviewed literature on this topic to TickEncounter for consideration and possible listing on this page.
Abstract: Nymphal Ixodes scapularis Say are the principal vectors of Lyme disease spirochetes (Borrelia burgdorferi sensu stricto) in the eastern United States. Physicians frequently face the decision of whether or not to administer prophylactic antibiotics to human tick bite victims in Lyme disease endemic regions, based on the overall probability that such bites will result in infection with B. burgdorferi s.s. We evaluated the transmission dynamics of B. burgdorferi s.s. during the key third day of nymphal I. scapularis feeding, when the risk of transmission rapidly increases. The cumulative probability that 50% of infected ticks transmitted B. burgdorferi s.s. occurred at 68hof tick attachmentandour overall estimate that ahuman tick bite would result in transmission of B. burgdorferi s.s. was 2.4%.
Animal studies have shown an exponential increase in the risk of Borrelia burgdorferi infection after 48–72 h of deer tick attachment. Persons with tick bites were prospectively studied to determine if those with prolonged tick attachment constitute a high-risk group for infection. Ticks were identified, measured for engorgement, and assayed by polymerase chain reaction (PCR) for B. burgdorferi DNA. Duration of attachment was determined from the scutal index of engorgement. Of 316 submissions, 229 were deer ticks; 14% were positive by PCR. Paired sera and an intact tick for determination of duration of attachment were available for 105 subjects (109 bites). There were 4 human cases (3.7% of bites) of B. burgdorferi infection. The incidence was significantly higher for duration of attachment ¤72 h than for 72 h: 3 (20%) of 15 vs. 1 (1.1%) of 94 (P .008; odds ratio, 23.3; 95% confidence interval, 2.2–242). PCR was an unreliable predictor of infection. Tick identification and measurement of engorgement can be used to identify a small, high-risk subset of persons who may benefit from antibiotic prophylaxis.
Abstract The duration of tick attachment is one factor associated with risk for human infection caused by several tick-borne pathogens. We measured tick engorgement indices at known time intervals after tick attachment and used these indices to determine the length of time that ticks were attached to tick-bite victims in selected Rhode Island and Pennsylvania communities where the agents of Lyme disease and human babesiosis occur. The total body length and width as well as the length and width of the scutum were measured on nymphal and adult female Ixodes scapularis Say removed from laboratory animals at 0, 12, 24, 36, 48, 60, and 72 h after their attachment. Three engorgement indices were calculated at each time interval. In addition, engorgement indices measurements were recorded for 504 ticks submitted to a commercial laboratory for pathogen detection testing between 1990 and 1992. No detectable change was observed in the average engorgement indices for either nymphal or adult ticks between 0 and 24 h of attachment using any of the engorgement indices. After 24 h of tick attachment, all engorgement indices continuously increased; average indices for nymphs attached 36, 48, and 60 h were significantly different from those attached S24 h and from each other. Similarly, average engorgement indices for adult ticks attached S36 h were significantly different from those attached for 48 h or more. More than 60% of tick-bite victims removed adult ticks by 36 h of attachment, but only 10% found and removed the smaller nymphal ticks within the first 24 h of tick feeding. The duration of tick attachment may serve as a useful predictor of risk for acquiring various infections, such as Lyme disease and babesiosis, transmitted by /. scapularis. Regression equations developed herein correlate tick engorgement indices with duration of feeding. A table containing specific engorgement index prediction intervals calculated for both nymphs and adults will allow the practitioner or clinical laboratory to use easily measured tick engorgement indices to predict transmission risk by determining the duration of feeding by individual ticks.
Abstract: Ticks are not crawling needles, merely delivering infectious agents to vertebrate hosts. A sophisticated interplay takes place between ticks, pathogens, and vertebrate hosts. The relationship between Ixodes ticks and the Lyme disease spirochetes they transmit involves subtle changes in spirochete populations that maximize their chances of being transmitted. An understanding of this complex interplay will, hopefully, allow the development of new tools to block transmission of tick-borne agents.
Regression equations, based on scutal index (body length/scutal width), were developed to determine the duration of attachment for nymphal and adult female Ixodes scapularis ticks. Feeding times were calculated for 444 nymphal and 300 female ticks submitted by bite victims between 1985 and 1989 in Westchester County, New York, an area where Lyme disease is highly endemic. Nymphs were attached for a mean of 34.7 hours, with 26.8% removed after 48 hours, the critical time for transmission of Borrelia burgdorferi. Attachment times increased with victim age class (Kruskal-Wallis test, p < 0.05). Mean duration of attachment for female ticks (28.7 hours) was significantly less (Kruskal-Wallis test, p < 0.05) than that for nymphs, with 23.3% attached for more than 48 hours. The 0- to 9-year age class had the highest proportion (37.1%) of females attached for more than 48 hours. Nymphs remain attached to adult tick-bite victims longer than they remain attached to children. However, children have a high risk of acquiring Lyme disease because they receive more nymphal bites and also because they are less likely to have female ticks removed in time to prevent transmission. Am J Epidemiol 1996;143:187-92.
Nymphal Ixodes dammini transmitted Borrelia burgdorferi to 1 of 14 rodents exposed for 24 h, 5 of 14 rodents exposed for 48 h, and 13 of 14 rodents exposed for -72 h. Prompt removal of attached ticks is a prudent public health measure, especially in regions where Lyme disease is endemic.