Gray squirrel a reservoir host of Bb in CA?

Western Gray Squirrel (Rodentia: Sciuridae): A Primary Reservoir Host
of Borrelia burgdorferi in Californian Oak Woodlands?

Authors: Lane, Robert S.; Mun, Jeomhee; Eisen, Rebecca J.; Eisen, Lars

Source: Journal of Medical Entomology, May 2005, vol. 42, no. 3, pp.
388-396(9)

Publisher: Entomological Society of America



Abstract:
In California, dense woodlands have been recognized as important
biotopes where humans are exposed to the nymphal stage of the western
blacklegged tick, Ixodes pacificus Cooley & Kohls, the primary vector
of the Lyme disease spirochete Borrelia burgdorferi sensu stricto
(s.s.), in the far-western United States. To identify the principal
reservoir host(s) of this spirochete, and of closely related
spirochetes in the B. burgdorferi sensu lato (s.l.) complex, in dense
woodlands in Mendocino County, California, ap50 species of birds and
mammals, including wood rats and kangaroo rats, were evaluated as
potential hosts for vector ticks and borreliae in 2002 and 2003.
Although polymerase chain reaction (PCR) and sequencing analyses
revealed that many vertebrate species had been exposed to one or more
members of the B. burgdorferi s.l. spirochetal complex, only the
western gray squirrel, Sciurus griseus, fulfilled the major criteria
for a reservoir host of B. burgdorferi s.s.

Ear-punch biopsies from eight of 10 squirrels collected from five
separate woodlands were PCR-positive for B. burgdorferi s.s., 47% of I.
pacificus larvae (n = 64) and 31% of nymphs (n = 49) removed from
squirrels contained B. burgdorferi s.l., and the engorgement status of
I. pacificus larvae was associated positively with acquisition of
spirochetes. Overall, 83 and 100% of the amplicons sequenced from
PCR-positive I. pacificus larvae and nymphs, respectively, were
identified as B. burgdorferi s.s. Among the five remaining positive I.
pacificus larvae, three contained B. bissettii and two had
uncharacterized B. burgdorferi s.l. Borrelia burgdorferi s.s. was
detected in one of five larvae and zero of two nymphs of the Pacific
Coast tick, Dermacentor occidentalis Marx, that likewise had been
removed from squirrels.

The rickettsial agent of human anaplasmosis, Anaplasma
phagocytophilum, was detected in the blood or ear biopsies of two
squirrels and in one (1.6%) of 64 I. pacificus larvae and two (4.1%) of
49 nymphs obtained from squirrels. The one rickettsial-positive larva
was coinfected with B. burgdorferi s.s. The apparently high reservoir
potential of S. griseus for B. burgdorferi s.s., plus the fact that the
geographic distribution of this squirrel coincides well with that of
most reported human cases of Lyme disease in this region, indicated
that it may be essential for maintaining foci of B. burgdorferi s.s. in
certain types of woodlands. The findings with respect to A.
phagocytophilum, although of less certain significance, suggest that S.
griseus could serve as a secondary host of this rickettsia.

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