Once Bit Twice Smitten: The Duration of Tick Attachment and Transmission of Lyme Disease and HGE
Abstract & Commentary
Synopsis: The need for prolonged tick attachment for pathogen transmission is confirmed in Lyme disease. The HGE pathogen is transmitted more rapidly.
Source: des Vignes F, et al. J Infect Dis. 2001;183:773-778.
In this study from yale, the cdc, and the new Jersey Department of Health, the central question is how long need a tick attach to transmit Borrelia burgdorferi and Ehrlichia phagocytophilia, the agent of human granulocytic ehrilichiosis (HGE).
There were several interesting aspects of the study. The ticks used for study were field collected from several Lyme infested areas. Ticks were allowed to feed on 4-week-old mice for 24-hour intervals up to 96 hours. Ticks were cultured for B burgdorferi and also tested for Borrelia DNA and Ehrlichia DNA by PCR. Infections of mice were proven by PCR testing of mouse blood.
Of 228 ticks collected in the field, 30% were infected with culturable B burgdorferi. In order for mice to be infected, ticks had to remain attached for a minimum of 48 hours. Infection efficiency was only 12.5% at 48 hours but rose steeply to 79% at 72 hours. In a complex calculation, based on the percentage of nymphs infected and the published duration of attachment, des Vignes and associates estimate that only 4.6% of nymphal ticks, once removed, will transmit B burgdorferi.
The interesting part of the study came when looking at dual infection. Those ticks that were dually infected did not transmit B burgdorferi at 24 hours but in 2 of 3 attempts did transmit Ehrlichia.
Comment by Joseph F. John, MD
Where I live in central New Jersey, there are a lot of people and a lot of ticks. Trying to prevent Lyme disease almost seems futile, particularly when you consider the tiny size of nymphal ticks. Okay, you say, but this study shows that the nymphs have to stay on at least 48 hours to transmit Lyme disease, and by then the wary may have a chance to spot the dot that is the engorging nymph. I say, okay, maybe so. But this study has showstopping data, although the data are small: Erhlichia, unlike Borrelia, are transmitted more easily at 24 hours, and that, I claim, is a very hard infection to prevent. More troublesome is the observation in this study that a single nymph attached for 72 hours transmitted both organisms, an observation (of dual infection) reported several years ago by Duffy and associates1 and recently further corroborated with the additional recognition that the vector was indeed the Ixodes scapularis tick.2
Dr. John is Professor of Medicine and Microbiology, University of Medicine & Dentistry of New Jersey, Robert Wood Johnson Medical School, New Brunswick, NJ.
1. Duffy J, et al. Lancet. 1997;349:399.
2. Levin ML, Fish D. Infect Immun. 2000;68:2183-2186.