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Adult bee diseases

Nosemosis

Vairimorpha (Nosema) apis and ceranae

Severity : High NotifiableN. apis: late winter and spring; N. ceranae: all yearReview in progress
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Key points

  • An intestinal disease of adult bees caused by microsporidia.
  • Nosema apis mainly causes dysentery in spring; Nosema ceranae causes quieter dwindling.
  • Reliable diagnosis only under the microscope, on a sample of bees.
  • In France, Nosema apis disease is a regulated disease.

Nosema disease affects the gut of adult bees. It shortens their lives and weakens the colony, especially at the end of winter.

The agents

Two microsporidia, parasites related to fungi, infect honey bees. They have been reclassified in the genus Vairimorpha, but the name Nosema is still widely used2.

  • Nosema apis: the long-established European species, linked to late-winter dysentery.
  • Nosema ceranae: originally from the Asian honey bee, now widespread worldwide, often without dysentery but with gradual dwindling1.

Bees become infected by swallowing spores, cleaning soiled combs or sharing food.

Symptoms

  • Faecal staining on combs, floor and hive front (especially with N. apis).
  • Bees crawling outside the hive, swollen abdomens.
  • Slow spring build-up, a population that fails to take off.
  • With N. ceranae: colonies that dwindle without obvious signs.
Photo needed — Combs and hive front stained with dysentery at the end of winter.

Diagnosis

Symptoms are not enough. The crushed abdomens of about 30 forager bees are examined under the microscope for spores; a laboratory test distinguishes the two species3.

Regulation

In France, Nosema apis disease is a regulated bee disease: a suspicion must be reported to the veterinary services4. Other countries have their own rules.

Prevention and management

No medicine is authorised against Nosema disease in the European Union. Measures are hygienic:

  1. Replace brood combs regularly.
  2. Winter strong colonies with good-quality stores.
  3. Place hives in a dry, sunny spot.
  4. Remove and clean soiled combs.
  5. Control varroa, which worsens weakening5.

References

  1. Fries I. (2010). Nosema ceranae in European honey bees (Apis mellifera). Journal of Invertebrate Pathology 103: S73-S79.
  2. Tokarev Y.S. et al. (2020). A formal redefinition of the genera Nosema and Vairimorpha (Microsporidia: Nosematidae) and reassignment of species based on molecular phylogenetics. Journal of Invertebrate Pathology 169: 107279.
  3. WOAH. Terrestrial Manual, chapter 3.2.4: Nosemosis of honey bees.
  4. Apiculture 69. Regulatory reminder: apiary declaration and regulated diseases (article D223-21 of the French Rural Code), in French. apiculture69.fr
  5. FAO, IZSLT, Apimondia, CAAS (2021). Good beekeeping practices for sustainable apiculture. FAO Animal Production and Health Guidelines No. 25.

Updated : October 8, 2026
Written by : Apisanitas editorial team
Reviewed by : Review in progress