be compared with infections with N. apis. More strikingly,
we know N. ceranae has been present in European honey
bee populations for more than a decade (Paxton et al,
2007). In the United States of America (USA) it has been
present even longer (Chen et al, 2008) without the dramatic
effects reported from Spain where the infections are
claimed to be the direct cause for colony collapse (Higes
et al, 2008). This clear link is not present in the USA where
colony losses have also occurred (Cox-Foster et al, 2007).
Undoubtedly more research and surveying is needed before
we can determine what impact this parasite, comparatively
new in European honey bee populations, will have on
apiculture at large. It is conceivable that there may be
pronounced regional differences and that, for unknown
reasons, N. ceranae might prove to be more virulent in
warmer climates compared with N. apis. For the time being,
however, we should follow regional advice that has been
offered for controlling N. apis infections, until we know the
real difference in transmission and virulence between
N. apis and N. ceranae.
Fig 2. Spores of N. ceranae (A) and N. apis (B) in the
transmission electron microscope. The two nuclei are seen DIFFERENTIAL DIAGNOSIS OF N. CERANAE
inside the spore (D) along with the coiled polar filament AND N. APIS
(PF), part of the infection apparatus of the parasites.
Bar = 0.5 mm (from Fries et al, 2006) Microscopy is needed to diagnose microsporidial infections.
Macerated abdomens or just the intestinal tracts can be
is beekeeping with European bees (Fries et al, 2006, used in crude preparations with some water, where the
Chauzat et al, 2007, Klee et al, 2007, Huang et al, 2007, spores are easily seen in magnifications around X400.
Paxton et al, 2007, Chen et al, 2008, Williams et al, 2008). There is a consistent size difference between the spores of
the two species, with N. ceranae being slightly smaller than From recent examinations of historic samples it appears as
N. apis (Fries et al, 1996). if there is an ongoing process where N. ceranae is actually
replacing N. apis worldwide (Paxton et al, 2007). For The length of spores in squash preparations of N. ceranae
biodiversity reasons, I have suggested on occasion that we isolated from A. cerana is 4.7 ± 0.46 µm. The width of the
need to protect N. apis from extinction! All indications are spores is 2.7 ± 0.25 µm, range 2.3–3.0 µm, N=25 (Fries
that N. apis is now difficult to find in large parts of the et al, 1996). Although there is a slight overlap, with the
world, which may be one reason for the lack of comparative smallest N. apis spores being smaller than the largest
virulence data for the two parasites. N. ceranae spores, the average spore size of N. apis is
In Canada (Williams et al, 2008) and in Sweden (Fries and approximately 1 µm longer (Figure 2). The spores of
Forsgren, 2008) and possibly in Ireland, the British Isles N. ceranae sometimes appear slightly bent which gives a
and in Africa (Fries and Raina, 2003) pure infections of less consistent appearance compared with N. apis
N. apis can still be found, but may disappear as mixed (Figure 1). Although the difference between the two species
infections are also observed in many places. This can be seen in the light microscope, it may be difficult to
replacement process, along with limited comparative be certain of the diagnosis without reference slides. The fact
infection studies, suggests that N. ceranae may be more that mixed infections often occur makes it even more
virulent to honey bees than N. apis (Paxton et al, 2007). difficult to make a differential diagnosis using light
The driving forces behind this replacement process still microscopy.
remain to be unravelled since we do not yet know what
competitive advantage N. ceranae exhibits. The two parasites can also be easily distinguished by more
sophisticated methods, such as transmission electronRecent data from Spain, where colonies appear to die
microscopy and sequencing of the 16S SSU rRNA gene.within a year and a half when infected by N. ceranae unless
However, these methods are tools not normally available totreated with fumagillin (Higes et al, 2008), suggest
beekeepers and require well-equipped laboratories.beekeepers should pay close attention to nosema
infections. It should be noted that fumagillin treatment for CONCLUSION
control of nosema is not legal within the European
community since it is not a registered veterinary product. In conclusion, N. ceranae is established as a natural infection
These data from Spain strongly suggest extreme colony in populations of European honey bees and is now widely
virulence from N. ceranae infections. However, again, no distributed. The data at hand suggest that the parasite is not
comparative data are available where these infections can a new introduction but has been present in A. mellifera in
Page 10 Bee Craft digital January 2009
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