Hi to all,
This translated material was forwarded to me several days ago - Relating
to the developing problems in various regions of the US, it makes
interesting reading.
Peter
Nosema ceranae
Asian Nosema Disease Vector Confirmed – is this a new infestation or
only now discovered?
Translated from the original German with the permission of Dr Wolfgang
Ritter, Freiburg University by Eric McArthur MIL
Nosemosis(previously Nosematosis), which in acute cases causes diarrhoea
and short lived bees, which exhibit agitated crawling around in front of
the hive is a disease known to most beekeepers. The cause of the
disease is Nosema apis, which affects the mid gut of the Western
honeybee, Apis mellifera spp., and which is wide spread in virtually all
honeybee colonies. The disease is aggravated by long confinement in
the hive due to external unfavourable weather conditions, possible
worsened by badly positioned hives, which forces the bees to defecate in
the hive, which frequently results in heavy loss of bee life.
The Asian Variant
In 1996 a similar type of organism to N. apis was discovered on the
Asian honey bee Apis cerana and subsequently named Nosema ceranae.
Little is known at the present time about the symptoms and the course of
the infection in Asia. Until recently it was assumed that this disease
vector was specific to the Eastern honeybee, A. cerana. However in 2005
Chinese researchers reported that N.ceranae had been discovered in the
Western honeybee, A mellifera in Taiwan. In the same year the Castilla
– La Mancha Beekeeping Institute in Spain and the Veterinary Medicine
University in Madrid demonstrated for the first time that the disease
was present in European honeybee in Europe. In Spain the cases of
Nosemosis had risen constantly from 10% in 2000 to over 20% and 30% in
the following years reaching 88% in 2004. An important cause for the
huge honeybee colony losses in Spain was therefore suspected as being a
result of the N.ceranae infection, after it was discovered there. A
massive loss of adult bees was also observed in the apiaries (defined as
absconding), similar to the symptoms of heavy Varroa mite infestation.
Discoveries also in Germany
The question as to whether particular colony losses in Germany could
possibly be ascribed to N.ceranae is intended to be cleared up in
collaboration with the Audit Laboratory of the University of Freiburg
and the Spanish institutes around the end of the year 2005/2006. In the
meantime using molecular-genetic methods (PCR) the new Nosemosis vector
has been shown to be also present Germany in 8 of 10 tested apiaries.
Two apiaries in Baden – Württemburg, four in Bavaria and two in North
Rhein- Westfalia. The bees with the classic vector, N. apis came from
Thüringen and Bavaria.
In all these apiaries, irrespective of the disease vectors confirmed
later, severe problems occurred in spring, late summer and autumn of
2005. These problems lead to either to the death of most of the
colonies or of the whole apiary. There was evidence of a moderate to
severe Nosema infestation in all of the samples tested.
Clear symptoms of defecation and crawling were not present in all cases
investigated, however a heavy bee mortality occurred in every case.
The Mechanism of Infection Spread is Unclear
Both disease vectors, N. apis and N.ceranae cannot be differentiated
using the present routine microscopic examination. Only with the use of
molecular genetic procedures is it possible to separate the two.
The following questions arise from this situation:
· Where did N. ceranae originate? Although this species carries
the cerana name, because it was initially discovered on the Asian
honeybee, this is not necessarily a statement on its initial spread.
· Was the disease only recently brought in does it actually
cause high bee mortality, as the Spanish presume, due to its extreme
virulence.
· Or is it a long standing condition, which only now we have
been able to differentiate from the traditional N. apis?
· Is the actual course of the disease with the increase of
Nosema infestation more severe because the colonies are weaker and more
vulnerable due to the predations of the Varroa mite and other factors?
We have tested samples from some 500 apiaries in Germany, Italy
(Tirol), Austria and Switzerland since 2002, which suffered high or
total losses. Where residual bees were present, we were seldom able to
confirm Nosemosis. During the years 2002/03 where high winter losses
occurred the disease level was 38%. This year according to current
tests the proportion appears to be higher. Consequently we are able at
this time to confirm the Spanish results only with regard to the
increase in Nosemosis.
Over the past 2 to 3 years, however we have observed, that the course of
Nosemosis has actually altered. Contrary to the classic insidious form
of Nosemosis, crawling and losses occur during the whole year.
Furthermore it is being observed this winter that colonies are dying
within a very short time scale Beekeepers are finding contrary to
typical Varroa infestation damage, hives full of dead bees. A further
observation was made that this winter that colonies in many apiaries
were undertaking relatively strong cleansing flights, even at
temperatures as low as 4 C. At this stage it is not possible to
conclusively link these flights with the new form of Nosemosis.
There are still many questions which we are attempting to clarify with
our on-going investigations. According to our current assessment the
whole situation appears to be similar to the classic Nosemosis
condition. We are of the opinion therefore, that the usual preventative
measures relative to Varroa treatment as well as the optimisation of the
factors relating to apiary location should still play a dominant role in
beekeeping management - in order to come to terms with the Nosemosis
problem.
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