Duration of tick attachment required for transmission of granulocytic ehrlichiosis.

Deer tick-transmitted pathogens such as Lyme disease spirochetes and babesiae appear to require a period of reactivation and replication during the tick's blood meal before it is able to infect a host. The duration of nymphal tick attachment that is required for transmission of the agent of human granulocytic ehrlichiosis (HGE) was determined by removing feeding ticks from mice at various time points. As with spirochetes and babesiae, ehrlichiae infected few mice when ticks were removed prior to 36 h of tick attachment. This "grace period" may serve as a modifying factor in the epidemiology of this newly emergent zoonosis and help physicians make informed decisions concerning management of tick bites in HGE-endemic areas.