As species of microsporidia like N. apis and N. ceranae are often
difficult to distinguish morphologically, our first aim was to develop
a rapid PCR–RFLP method to distinguish between N. apis, Nosema bombi
and N. ceranae, the only three members of the large genus Nosema that
have been detected in bees. Our second aim was to use the method to
screen microsporidian isolates from A. cerana and A. mellifera from
across the world to reveal their past and current distribution.

 A. mellifera was formerly parasitized by N. apis alone and not N.
ceranae and that N. ceranae should consequently be considered an
exotic parasite of A. mellifera. Our data support the view that N.
bombi, on the other hand, is not a parasite of honey bees. The current
incidence of N. ceranae in A. mellifera provides strong support for
the view that this microsporidian is an emergent pathogen of the
western honey bee, most probably due to a host jump from A. cerana to
A. mellifera.

 The main reason for such a rapid expansion in the range of N. ceranae
in A. mellifera is probably the world trade in living honey bees, a
reason which also explains the rapid spread of V. destructor around
the world (Bailey and Ball, 1991). Microsporidia have also been
implicated in the demise of native North American bumble bees (Bombus
spp.) through so-called pathogen spill-over from commercially reared
bumble bees used in greenhouse pollination; in this instance, one of
the pathogens concerned is N. bombi, a microsporidium widespread in
European Bombus spp.

Trade in honey bee hive products may also play a role in the dispersal
of N. ceranae. The increased mobility of people, goods and livestock
is thought to account for the geographical and host range expansion of
numerous pathogens in human and animal populations or ecosystems.
Recent reports of honey bee colony losses in southern and central
Europe combined with Higes et al.'s observations of N. ceranae in
dying Spanish colonies and Higes et al.'s experimental demonstration
of the virulence of N. ceranae for caged A. mellifera give cause for
concern.

Over the past few years, many beekeepers in Europe have noticed a
change in the course of nosema disease in their colonies, especially
loss of honey bees the whole year around and quick die off of colonies
in the winter time. Nosema apis, on the other hand, generally affects
colonies during spring.


SEE:
"Widespread dispersal of the microsporidian Nosema ceranae, an
emergent pathogen of the western honey bee, Apis mellifera" by Julia
Klee, et al

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