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Nosema Infections in European Honey
Ingemar Fries, PhD
Department of Entomology, the Swedish University of Agricultural Sciences, Uppsala
ALL MICROSPORIDIA are eukaryotic obligate intracellular accident in 1994 in China during experiments to elucidate if
pathogens that infect a wide variety of animals and cell N. apis could cross-infect A. cerana. It was not possible to
find control bees of A. cerana which were one hundred pertypes, including insect hosts. From a taxonomic point of
cent free of microsporidia. Upon closer examination itview they have previously been placed in the
turned out that a new distinct microsporidium was infecting subkingdom Protozoa (Levin et al, 1980) but more
the Asian honey bee. Cross-infection experiments
recent molecular evidence demonstrates that they are demonstrated further that both species of microsporidia
more related to fungi (Lee et al, 2008). were infective for both host species but that N. ceranae did
better in A. mellifera than N. apis did in A. cerana (Fries and Thus, microsporidia should be regarded as a form of highly
Feng, 1995; Fries, 1997). specialised parasitic fungi, whose infection apparatus
makes them unique and morphologically distinct. NOSEMA APIS IN EUROPEAN HONEY BEES
Approximately 1200 different species of microsporidia in
about 500 genera are described (Keeling and Fast, 2002), N. apis infections in honey bees may vary considerably in
undoubtedly only a small fraction of the actual number. their impact and often do not cause measurable damage.
This is often the case with microsporidial infections of insects From pollinating insects only four species have been
where chronic infections are common in host populationscharacterised, Nosema bombi, infecting bumblebees
(Becnell and Andreadis, 1999). However, under certain(Fantham and Porter, 1914), Antonospora scoticae infecting
conditions, N. apis infections may become epidemic andthe sand bee Andrena scotica (Fries et al, 1999), Nosema
actually be fatal to infected colonies. apis infecting the European honey bee Apis mellifera
(Zander, 1909) and Nosema ceranae infecting the Asian It has been suggested that the impact of this parasite is
honey bee Apis cerana (Fries et al, 1996). more serious in temperate climates. It may be linked to theduration of confinement in such colder climates, with a
The relatively recently described N. ceranae was detected by pronounced seasonality, the highest level of infections
being in the spring (Bailey and Ball, 1991; Fries, 1997).
Fig 1. Spores of N. ceranae (A) and N. apis (B) in light microscopy However, recent data from Africa (Fries and Raina, 2003)
squash preparations. Bar = 5 mm (from Fries et al, 2006) demonstrate that N. apis may also be prevalent all year
round under sub-tropical conditions, where the bees may
be flying throughout the year.
Although experimentally cross-infective (Fries and Feng,
a 1995; Fries, 1997), it was believed up until 2005 that thee
R natural host range for N. apis was limited to the Europeanl
t honey bee and N. ceranae was restricted to the Asianlu
cip honey bee. In spite of this, in 2005, European honey bees
A f
o l were found to harbour natural infections of N. ceranae both
uo in Taiwan (Huang et al, 2007) and in Spain (Higes et al,
ht 2006). f
o s
i The infections in Spain are of particular interest since and
e e
h increasing level of microsporidial infections had beent f
o n experienced for several years (Martin et al, 2005). Because of
si this, a limited number of samples were sequenced in 2005
p and 10 out of 11 samples matched the original genee
h sequence deposited in GenBank for N. ceranae (Higes et al,ti
w d 2006; Fries et al, 1996, accession number U26533). This was
ud the first detection of N. ceranae in European honey bees in
eR Europe. Since then this parasite has been found to be
BI widespread all across the world on all continents where there
Bee Craft digital January 2009 Page 9
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