Short report: duration of tick attachment required for transmission
of powassan virus by deer ticks.

    Ebel GD, Kramer LD.

    Arbovirus Laboratories, Wadsworth Center, New York State Department
of Health, Slingerlands, New York 12159, USA.

    Infected deer ticks (Ixodes scapularis) were allowed to attach to
naive mice for variable lengths of time to determine the duration of
tick attachment required for Powassan (POW) virus transmission to
occur. Viral load in engorged larvae detaching from viremic mice and in
resulting nymphs was also monitored. Ninety percent of larval ticks
acquired POW virus from mice that had been intraperitoneally inoculated
with 10(5) plaque-forming units (PFU). Engorged larvae contained
approximately 10 PFU. Transstadial transmission efficiency was 22%,
resulting in approximately 20% infection in nymphs that had fed as
larvae on viremic mice. Titer increased approximately 100-fold during
molting. Nymphal deer ticks efficiently transmitted POW virus to naive
mice after as few as 15 minutes of attachment, suggesting that unlike
Borrelia burgdorferi, Babesia microti, and Anaplasma phagocytophilum,
no grace period exists between tick attachment and POW virus
transmission.

    PMID: 15381804 [PubMed - indexed for MEDLINE]

(I have a feeling this was posted before, but is a good one, so doing
it again.  Note that free full text article available at

http://www.***.com/

and I am not so sure about grace periods in babesia, lyme, ehrlichia
either.)