Effect of tick removal on transmission of Borrelia burgdorferi and Ehrlichia phagocytophila by Ixodes scapularis nymphs

The effect of feeding duration on pathogen transmission was studied for ind ividual ticks infected with either laboratory or field strains of the Lyme disease spirochete Borrelia burgdorferi and field strains of Ehrlichia phag ocytophila, an agent of human granulocytic ehrlichiosis. Infected nymphal I xodes scapularis were allowed to feed individually on mice, and equal numbe rs were removed at 24-h intervals for less than or equal to 96 h. Mice were assayed for infection by culture, serologic testing, and polymerase chain reaction (PCR) analysis. Fed ticks were assayed by culture or PCR analysis. Transmission of B. burgdorferi did not occur during the first 24 h among 6 6 attempts, with maximum transmission occurring between 48 and 72 h. A mode l estimating the probability of infection from individual ticks removed by patients in a Lyme disease-endemic area yielded an overall probability of 4 .6%. Infected I. scapularis nymphs transmitted E. phagocytophila within 24 h in 2 of 3 attempts, which indicates that daily tick removal may not be ad equate to prevent human infection with this agent.