California 2005: gray squirrel: a primary reservoir host of Bb in Californian oak woodlands?

1: J Med Entomol. 2005 May;42(3):388-96. Related Articles, Links


Western gray squirrel (Rodentia: Sciuridae): a primary reservoir host
of Borrelia burgdorferi in Californian oak woodlands?

Lane RS, Mun J, Eisen RJ, Eisen L.

Division of Insect Biology, Department of Environmental Science, Policy
and Management, University of California, Berkeley, CA 94720, USA.
blane@xxxxxxxxxxxxxxxxxxx

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, approximately 50 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.

PMID: 15962792 [PubMed - in process]

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