The major genetic group of
Toxoplasma gondii
, known as type I, generally
displays high lethality in laboratory
Mus musculus
(mouse) strains, with
few exceptions. However, because rodents are the primary reservoir hosts for
T.
gondii
, if this characteristic manifests in the wild, type I strains would be
extinct. Therefore, we hypothesized that populations of wild rodents capable of harboring
type I
T. gondii
asymptomatically exist globally and are not limited to a
few localized areas, as previously thought. The strength of mouse resistance to
T.
gondii
is known to depend on the affinity of the mouse-expressed
immunity-related GTPases B2 (IRGB2) protein for the
T. gondii
-expressed
rphoptry protein 5B (ROP5B) protein. Therefore, the
Irgb2
gene sequences
of 12 individuals mice captured at two animal farms in Gifu Prefecture, and on an island
in Okinawa Prefecture, Japan were determined, and subjected to a molecular phylogenetic
analysis together with those of various mouse strains worldwide. The Irgb2 gene of
M. musculus
individuals captured on one farm and one island showed
diverse sequences. The sequences from two individual mice captured in an animal farm
formed a single clade with a wild mouse derived CAST/EiJ strain, known for its exceptional
resistance to type I
T. gondii
lethality. These results suggest that
M. musuculus
individuals resistant to the Type I
T.
gondii
strain may be present in Japan, in addition to the previously known
populations in South Asia, Thailand and India.