The nosema disease is a parasitic disease of adult honey bees (apis mellifera) caused by the described species of microsporidia, Nosema apis and Nosema ceranae, which in adverse living conditions forms spores. Honeybees afflicted with nosemosis start to forage earlier, while pathological changes of their mid-gut epithelial cells, as well as digestive and metabolic disorders, cause malnutrition leading to premature deaths. Spores enter the digestive tract of bees via infected food and drink or on occasions of social food exchange with other bees. The most common source of infection include unsanitary water supply, honeycomb marked with faeces of infected bees, and contaminated honey. After reaching the mid gut, Nosema sp. Spores germinate under the influence of diverse chemical stimuli and their vegetive form invades the epithelial cells of the mid-gut where they multiply.
Part of the spores is expelled from destroyed epithelial cells of the gut via excrements and part remains in the lumen where they take vegetive form and invade previously healthy epithelial cells of the mid-gut. Consequently, bee are constantly hungry and take larger quantities of food which accumulates in their rectums as sweet faecal matter infected with spores. New Nosema ceranae is highly pathogenic and there are usually no visible symptoms of diarrhoea or adult bee deaths and there is a lack of seasonality in the diagnosis, and little is known about the pathogenicity. Factors favouring the spread of the disease include robbery in honey bee colonies, and bad beekeeping practices, as well as sudden temperature fluctuations, poor pasture, disturbance, and frequent movements of honeybee colonies.
Conditions which also influence the spreading of the disease are the long lasting impossibility of cleansing flights during the winter and the honeydew honey which is brought into the hive in the autumn and the beekeepers unable to extract on time.
The diseases arise early in the spring. Many dead honeybees are observed around the hive, but also in the hive, weakening the hive and very often the queen bee dies. Faecal matter in the form of diarrhoea, which is the source of further infection, often can be observed on the frames, honeycomb and the exterior woodwork of the hive.