Posted 4 March 06
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:
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
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