Nosema disease is an infectious diarrhoeal disease of bees caused by the microsporidia (nematodes) Nosema apis or N. ceranae. In the Czech Republic, nosema is present in up to 50% of bee colonies.
Nosematosis is not a dangerous disease of bees and therefore does not have to be reported to the Veterinary Administration. The disease can have a negative impact on the colony.
Nosema attacks the cells of the intestinal lining and undigested food causes diarrhoea in bees. Infectious stages - spores that can remain infectious for up to two years in the faeces - are shed into the environment with the faeces. Infection is spread in the hive by ingestion of faeces, contaminated food, moulting, colony joining, introduction of a new queen or contaminated equipment.
Diagnosis of Nosema spp. is made microscopically from smears taken from the hindquarters of at least 30 diseased bees. The oval spores are only a few micrometres in size.