The BeeHolder, January 2010

Two Nosema species have been identified in honey bees in England and Wales, Nosema apis and more recently the Asian species Nosema ceranae. Both are highly specialised parasitic Micro Sporidian fungal pathogens. Nosema spp. Invade the digestive cells lining the mid-gut of the bee, there they multiply rapidly and within a few days the cells are packed with spores, the resting stage of the parasite. When the host cell ruptures, it sheds the spores into the gut where they accumulate in masses, to be later excreted by the bees. If spores from the excreta are picked up and swallowed by another bee, they can germinate and once more become active, starting another round of infection and multiplication.

Symptoms of Nosema

There are no outward symptoms of the disease. Dysentery is often seen in association with N. apis infections; this may be seen as ‘spotting’ at the hive entrance or across the frames. The dysentery is not caused by the pathogen, but as a consequence of infection and can be exacerbated during periods of prolonged confinement during inclement weather, especially during the spring. This can lead to the bees being forced to defecate in the hive, therefore contaminating it further. In Spain it has been reported that N. ceranae infections are characterised by a progressive reduction in the number of bees in a colony until the point of collapse. The beekeeper may also see a significant decline in colony productivity. In the final phase of decline, secondary diseases frequently appear, including chalk brood and American foul brood. Eventually the affected colonies contain insufficient bees to carry out basic colony tasks and they collapse. Mortality in front of the hives is not a frequent symptom of N. ceranae infection. Dysentery and visible adult bee mortality in front of the hives are reported to be absent in N. ceranae infections. Dwindling can sometimes be rapid or take place over several months. Nosema is readily spread through the use of contaminated combs. The spores can remain viable for up to a year, it is therefore important not to transfer contaminated combs between colonies and as always to practice good husbandry and apiary management, maintaining vigorous, healthy stocks, which are better able to withstand infestations.

Diagnosis and Treatment

The simplest method of diagnosis of infections is by microscopic examination. Both N. apis and N. ceranae can be identified in adult bee samples using a standard adult disease screen - under the light microscope the spores of N. apis and N. ceranae appear as white/green, rice shaped bodies. However, both species are virtually identical when viewed using conventional microscopy, but can be distinguished by an expert eye. However, more accurate discriminatory tests are available which detect differences between the two species using genetic methods Currently treatment with the antibiotic Fumidil B available in the UK is an effective control against both Nosema species. As with all medicines ensure that the label instructions are followed.

Apologies to all those who have already read this article at BeeBase the website of the National Bee Unit www.nationalbeeunit.com . All beekeepers should be registered at BeeBase and use the facilities to get the latest informed information on bees. (Ed)