Nosema ceranae Giles Budge, National Unit, Central Science Laboratory, York

What is ceranae and how do you test for it?

NOSEMA CERANAE has been termed the ‘Asian variant’ WHAT ARE THE CLINICAL SYMPTOMS OF of a more familiar pathogen, , N. CERANAE? and was originally described in 1996. Both species are A good description of the disease has come from a paper microsporidial pathogens that are thought to represent written in French by leading Spanish researchers: very primitive, but highly specialised parasitic fungi. Both species exist as spores which fire a tube into the ‘What we are calling dwindling syndrome is not a new phenomenon. We first noticed losses in the late 1990s but cells of the honey bee gut wall. The pathogen then the problem became serious in autumn/winter 2004 and reproduces by injecting genetic material into cells of the spring 2005. This phenomenon is characterised by a gut wall and forming new spores within the host cells. progressive reduction in the number of in a colony with Both N. apis and N. ceranae can be identified in adult bee no apparent cause, until the point of collapse. The beekeeper samples using a standard adult disease screen. However, may well also note a decline in colony productivity. In the they are very similar when viewed using conventional final phase of this decline, secondary diseases frequently microscopy, therefore species discrimination benefits from appear, including chalk brood and American foul brood. more sensitive tests. Several tests are available which focus Eventually the affected colonies contain insufficient bees to on the detection of species-specific genetic material. CSL carry out basic colony tasks and the colonies collapse. (Central Science Laboratory) staff have advanced these Mortality in front of the hives is not a frequent symptom of detection methods by developing a method based on N. ceranae infection and there are usually no symptoms of real-time PCR (polymerase chain reaction), a sensitive diarrhoea or visible adult bee deaths. method which can detect and quantify low levels of pathogen infection. Sometimes the disease affects the whole apiary and other times only specific colonies will show symptoms. Dwindling WHAT IS THE EUROPEAN DISTRIBUTION? sometimes occurs rapidly but may also occur over several months. In general, the beekeeper observes a lack of vigour N. ceranae is already widely distributed in Europe, having and fitness of the colonies.’ been confirmed in many countries including Denmark, Finland, France, Germany, Greece, Italy, Serbia, Spain, DOES N. CERANAE EQUAL CCD? Sweden and Switzerland. Scientists have only recently developed diagnostic tests for this pathogen so, although it Leading US researchers found N. apis to be more highly looks like it has spread rapidly, it would be more accurate associated with CCD () than to say that our ability to detect it has spread rapidly. N. ceranae.

Nosema ceranae (left) and Nosema apis (right) with a single spore inset (x 400 and x 1000 magnification, respectively) Courtesy of the National Bee Unit Bee Craft January 2008 Page 7 N. ceranae may well be a WHAT CAN YOU DO? identicaltothatforN. apis. estimate the prevalence and keyplayerinCCD.However, The usual veterinary impact of both Nosema it is likely to be acting in N. ceranae infections have medicine is equally effective species across England and concert with other been reported NOT to show against both Nosema Wales. As part of this pathogens or conditions. typical signs of Nosema species therefore, process, additional samples infection. For example, practically, management of will be collected by In Europe the situation is dysentery and crawling bees the disease N. ceranae is inspectors in the 2008 different. Abnormal colony may well be absent. thesameasthatdescribed season and screened for losses reported in Europe for N. apis. Therefore we both Nosema species. In have been attributed to the It is important to note that recommend a routine adult addition, historical samples presence of N. ceranae. the pathological data from bee disease screen for all stored at the Central N. ceranae was the reported Spanish apiaries are not colonies showing symptoms Science Laboratory will be cause of 20,000 colony consistent with a that cause concern and tested along with imported losses in the Salamanca fast-acting, short-duration indicate possible Nosema. bees. Such data will provide region of Spain in syndrome. More usually, a better indication of November 2004. signs of gradual Following the poor season geographical spread and depopulation, low honey we have all experienced as N. CERANAE timing of introduction. IS IN production and higher beekeepers, it is crucial that ENGLAND AND autumn/winter losses are colonies entered the coming Finally, with the permission WALES? more likely indicators of the winter period in fine fettle. of the beekeepers presence of this parasite. Your colonies need to have concerned, the condition of The National Bee Unit (NBU) A routine microscopic been well fed and other all affected colonies will be started screening samples assessment will confirm pests and diseases monitored. using real-time PCR assays controlled as effectively as infection of both Nosema For updates of this and in late November 2007, current treatments allow. species, but will not other current research, immediately after assay necessarily be able to please see the News and validation. Assay validation FUTURE RESEARCH distinguish between them. Research pages on the NBU was delayed due to the However, once diagnosed, The NBU will carry out a beebase website at absence of certified treatment for N. ceranae is more detailed survey to (http://beebase.csl.gov.uk). z reference material for and . N. apis N. ceranae Nosema Treatment – a note from the Editor In total, 309 samples have been tested for the Treatment to control Nosema apis in a colony of bees should be two-fold: firstly by good presence of both species husbandry, ie, by maintaining strong colonies with an effective system of comb renewal so using real-time PCR. All that combs are as new as possible; secondly by the administration of doses of an antibiotic, fumagillin, in the autumn feed of affected colonies. positive results were confirmed using published With a little training, the spore stage of Nosema can be identified. Abdomens of worker assays for the detection of bees are ground up in a mortar with a little water and a drop of the resulting liquid spread these pathogens. Positive onto a microscope slide. The tell-tale rice grain shapes can be seen using a microscope results have therefore been with a magnification of 400x. If you take a large enough sample of bees, you could confirmed using two or probably detect minute levels of Nosema in many colonies. For a realistic result, it is three methods, both based recommended that you use around 30 bees. on the detection of Fumagillin is sold as Fumidil B. It should be mixed with the winter feed. One dose is 14 lb species-specific DNA. Of of sugar made into winter feed with 7 pints of water (or the approximate metric these samples, 31 tested equivalent). The powder is very fine and tends to form little pellets on the surface of the positive for N. apis (10%), syrup. It must not be added to hot water or syrup as the high temperature deactivates the 14 for (4.5%) N. ceranae antibiotic. and 3 (1%) tested positive for both Nosema species. My advice is to make the syrup and let it cool until it feels just warm to the touch. Half fill a cup with dry sugar and add the dose of powder. Stir the two together. Add a little cool N. ceranae positives were water and stir to make a paste with the sugar grains breaking up the powder globules. confirmed across six Add more water, a little at a time, until the powder is thoroughly mixed. Put this into the counties of England syrup and stir well. ‘Wash’ out the cup with some syrup and your dose is ready. (Cornwall, Essex, Lincolnshire, Hertfordshire, Feed so that the dose is the last food received by the colony. Last food in – first eaten is Greater London, North the order of the day with bees so this helps to ensure that fumagillin is present in the Yorkshire) and three in bees’ guts throughout the winter and, more importantly, in the spring as well. Wales (Glamorgan, Powys, In the spring, colonies with Nosema should also be put into sterilised hives and have as Dyfed). many combs as possible renewed.

Page 8 Bee Craft January 2008