Nosemosis is a fungal disease of adult bees caused by Nosema spp. There are two different sub-species of Nosema that affect Apis mellifera with different prevalence depending on the area: Nosema apis and Nosema ceranae, responsible for two different forms of the disease.
Both N. apis and N. ceranae have a dormant stage, a long-lived spore.The spores are hardly morphologically distinguishable between the two species and represent the resistance and propagation form of the disease (Fig.1). Spores can remain infectious from a few days up to five years at low temperatures.
This practice describes the two forms of the disease caused by Nosema apis and Nosema ceranae, how they are transmitted. It also provides some indications on how to control the disease.


Fig. 1:The microscopic spores of N. ceranae are hardly distinguishable from those of N. apis

Fig. 1:The microscopic spores of N. ceranae are hardly distinguishable from those of N. apis


Nosema apis is responsible for the "classic" known form of the disease, which is widespread especially in cold and wet areas. It appears more easily during spring and in mismanaged hives during winter. It occurs mainly with a decrease of the colony population. The disease never affects the larval stages and seldom the queen.


N. apis spores, found in feces, are directly or indirectly ingested by adult bees and develop in the intestines of the bees affecting the digestive functions.The spores are expelled with feces and, once outside, they can be swallowed by other bees that become infected. This microsporidium also affects the nutrition glands, abruptly interrupting their secretion: the bees can no longer feed the brood and, consequently, it brings to a halt also the colony renewal.


After the contact of bees with N. apis the following infection symptoms will appear:

  • intestinal disorders, such as diarrhea (Fig.2);
  • the bees become unable to secrete the royal jelly;
  • the foraging bees reduce their activity, until it stops completely;
  • in the rare cases in which the queen is sick, egg-laying greatly decreases.

Fig. 2: Bee with diarrhea

Fig. 2: Bee with diarrhea

First there is a slow depopulation, the work decreases while the state of restlessness of the colony increases.

Some bees are no longer able to fly, they walk with their wings spread out in "K" form (Fig.3), paralysed, while other bees gather in small groups.

Fig. 3: Paralysed bee with wings spread out in "K" form

Finally, the presence of dead bees on the bottom of the hive with swollen abdomen and legs retracted below the chest can be observed (Fig.4). The running board of the hive entrance and the honeycombs will be smeared with diarrhea (Fig.5).

Fig. 4: Top - Dead bee with swollen abdomen and legs retracted below the chest; Bottom - Normal dead bee

Fig. 4: Top - Dead bee with swollen abdomen and legs retracted below the chest; Bottom - Normal dead bee

Fig. 5: The running board of the hive entrance and the honeycombs will be smeared with diarrhea

Fig. 5: The running board of the hive entrance and the honeycombs will be smeared with diarrhea


It is not easy to diagnose the disease in its early stages; the only suspicious sign is the presence of liquid excrement on the running board of the hive.

A field test consists of examining the colour of the terminal portion of the digestive system of some bees: in healthy bees it has a reddish colour, while in sick bees it is milky white (Fig 6). For examination the intestines are extracted together with the last segment of the abdomen. This sign, however, is seen only when the disease has already reached a certain severity. Only a laboratory test can make an early diagnosis by searching with the microscope the spores at intestinal level or directly on feces.

Figure 6 - Medium gut of healthy (left) and ill (right) bees.  


Transmission occurs primarily by fecal-oral route. N. apis can easily spread through the droppings of sick bees, especially within the hive.

The spread from hive to hive and apiary to apiary may occur through:

-       drifting of infected workers;

-       drone displacement;

-       looting of infected colonies;

-       interchanging infected honeycombs from a hive to another;

-       feeding of bees with contaminated honey;

-       use of infected materials or equipment.

This disease is influenced by many climatic factors:

  • bad weather increases the chances of infection among the bees of the same hive because it forces the bees indoors;
  • seasonal pattern can also affect the spread of infection. during long, cold winters and cold, rainy springs the bees may not find nectar and pollen;
  • frequent hive inspections with adverse weather conditions (e.g. winter season, windy or rainy weather) can trigger the onset of the disease as well as its propagation due to the induced stress;
  • the presence of other diseases (such as amebiasis or viruses) exacerbates the symptoms of nosema.


  • Prevent the infection by adopting good management practices and by taking special care when selecting the apiary location (non-humid, not exposed to cold winds) and the correct orientation of the hives (prefer sunny and slightly ventilated areas).
  • Adopt correct wintering measures (removing honeycombs not populated by bees, providing good quality food if necessary and applying appropriate treatments against varroa).
  • Place pollen plants near the hives that can provide protein food to the colony in the late summer and autumn.
  • In cold climates, keep the hives warm during wintering until late spring.
  • Use an adequate number of honeycombs in relation to the colony population.
  • Disturb the bees as little as possible during winter.

Unfortunately when N. apis occurs, the prognosis is frequently serious because its onset is almost always unnoticed and symptoms occur only at an advanced stage. Generally the affected colonies do not heal spontaneously, therefore the beekeeper’s intervention becomes necessary. If the disease is well developed, particularly in weak families its destruction is definitely suggested. It is possible to retrieve the materials after killing the bees, sterilising the hives and destroying the combs (with boiling water, soda 6% and blue flame). Peracetic acid is a natural wide spectrum disinfectant that can kill nosema spores and can be used to disinfect contaminated hives, frames, including frames with built combs and beekeeping material.  Peracetic acid based products are available commercially in different form (powder, spray, etc.) and should be used following instructions by the supplier.  Generally, the peracetic acid based product is dissolved in water and the beekeeping equipment is immerged in the solution, left in the solution for some time and then dried before re-use.  Some Peracetic acid based products are allowed in organic farming in Europe.  

Infected honey and pollen should absolutely not be used to feed other bees to avoid their infection. In case the affected family is very strong, move it in an area exposed to the sun (not windy and cold), with clean hive and combs thus decreasing the possibility of re-infection from diarrhea and provide proper feeding (e.g. molasses, herbs or medicated feed). The infected combs should be destroyed and the hive should be sterilised as mentioned above or destroyed. The honey can be used for human consumption. To destroy a hive and avoid further contamination, a hole deep at least 50 cm should be dug in the ground, the hive and combs should be burnt and the hole should be duly covered.


Nosema ceranae is a new species of microsporidium isolated for the first time in 1996 by Fries on Apis cerana, a bee species widespread in Southeast Asia.

In 2006 it was isolated for the first time by Higes in Apis mellifera. N. ceranae has spread in vast areas of Europe replacing the indigenous form of Nosema apis on Apis mellifera, resulting in quite different clinical signs from the classical nosemosis. Typical of this disease are the severe injuries and the absence of gastro-enteritis (diarrhea) as a typical symptom and the appearance of the disease in different periods from those of N. apis. It was listed among the possible causes of depopulation of the hives, even though its pathogenic effect on the honeybees is still unclear.


The ingestion of microsporidium by the bees occurs directly or indirectly (e.g. through honey contaminated by the spores). N. apis develops and attacks the intestines of the bees inducing malabsorption. The spores of N. ceranae are very resistant in the environment (they can withstand very cold or very hot temperatures), facilitating the re-infection of the colonies and the recurrence of the disease after a long time.


The disease can occur throughout the year. Typical is the absence of diarrhea in foraging bees. It seems that they go to die away from the hive, causing a progressive depopulation of the colonies (without noticing the presence of dead bees) until the total loss of the family.


The microscopic spores of N. ceranae are hardly morphologically distinguishable from those of N. apis. It is possible to make a diagnosis only through the PCR (polymerase chain reaction), a biology molecular technique, which allows the sequencing of a very specific and characteristic part of N. ceranae genome on the spores. Cost and availability of this exam depends on each country and laboratory.

See related technologies published on TECA by Apimondia and IZSLT on bee diseases:

  1. Good beekeeping practices
  2. Main diseases of honey bees
  3. Nosemosis
  4. Varroa mites (Varroatosis or Varroosis)
  5. AFB (American Foulbrood)
  6. EFB (European foulbrood)
  7. Bee viruses



Formato G. (Istituto Zooprofilattico Sperimentale del Lazio e della Toscana - Italy), Menegotto A. (Conservation Global - South Africa), Jannoni-Sebastianini R. (Apimondia - International Federation of Beekeepers’ Associations - Italy), Nosemosis, 2015

Further reading

Palazzetti M., La nosemosi. In “Aspetti igienico-sanitari in apicoltura” published by the Istituto Zooprofilattico Sperimentale del Lazio e della Toscana “M. Aleandri”, Italy, August 2007, 22-24

Ellis J., Honey Bee Research and Extension Lab at the University of Florida, Video Field Guide to Beekeeping – Nosema Disease, February 2012,

Created date

Wed, 17/06/2015 - 12:16



Apimondia, the International Federation of Beekeepers’ Associations, is the world organisation representing the interests of apiculture and aims to facilitate links between beekeepers, scientists and all involved with apiculture. Apimondia stems from the International Committee of Apicultural Congresses created in 1893 holding the first congress in 1897 in Belgium. Apimondia in its current institutional form was founded in the Netherlands in 1949 and its core business is the organisation of international apicultural congresses and symposia. Today Apimondia work remains truly international: Apimondia is run on a basis of co-operation between beekeepers and scientists from many countries as well as international organisations. A special feature of Apimondia is the wide range of working languages used in publications and at meetings.

You can also visit Apimondia linked websites to find out more:



Apimondia, la Federación Internacional de las Asociaciones de Apicultores, es la organización mundial que representa los intereses de la apicultura y su objetivo es facilitar los vínculos entre los apicultores, los científicos y todos los involucrados con la apicultura. Apimondia deriva del Comité Internacional de los Congresos Apícolas creado en 1893 y con la celebración del primer congreso en 1897 en Bélgica.  Apimondia, en su forma institucional actual, fue fundada en los Países Bajos en 1949 y su actividad principal es la organización de congresos y simposios apícolas internacionales. Hoy el trabajo de Apimondia permanece verdaderamente internacional: Apimondia realiza su programa sobre la base de la cooperación entre los apicultores y los científicos de muchos países, así como organizaciones internacionales. Una característica especial de Apimondia es la amplia gama de idiomas utilizados en las publicaciones y en las reuniones de trabajo.

Para más informes puede visitar los sitios web de Apimondia:

Contact person: 
Riccardo Jannoni-Sebastianini
Contact email: 
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IZSLT - Istituto Zooprofilattico Sperimentale del Lazio e della Toscana “Mariano Aleandri”

The Istituto Zooprofilattico Sperimentale del Lazio e della Toscana “Mariano Aleandri” (IZSLT) is a public body operating in the frame of the National Health Service with duties related to animal health and welfare and food safety. In such areas it provides services in the diagnosis of animal diseases and zoonoses, microbiological, chemical and physical controls over safety of foods, food production chains and animal feed. In the same areas it performs research, epidemiological surveillance, continuous training and international cooperation activities.

IZSLT's mission is to ensure that animal health and welfare, hygiene of farms, primary productions, safety of foods and animal feed comply with the relevant legislation.

To effectively fulfill its mission, the Institute carries out:

  • diagnostic service over animal diseases and zoonoses;
  • scientific and technical support to veterinary and public health services for controls on animals, food and feed;
  • laboratory tests to verify the health status of animals;
  • technical and scientific support to monitor veterinary medicines;
  • research on animal health and welfare, food safety and hygiene of farming and livestock products;
  • studies on animal welfare and development of alternatives to the use of animals in experiments;
  • studies to monitor the safety of food of animal origin and feed;
  • scientific and technological cooperation with other research institutes;
  • epidemiological surveillance on animal health and food safety, on livestock products and on environmental factors affecting the above;
  • studies on the health risks for humans linked to animals and animal products;
  • support, technical assistance and hygiene information to manufacturers of food of animal origin;
  • production of vaccines and laboratory diagnostics for the improvement of animal health.

In the frame of IZSLT activities, the Apiculture Unit’s mission ( is to certify and guarantee the health and welfare of bees, and the hygiene and safety of the hive products, through: diagnosis of bee diseases and analyses on hive products, support to Governmental Institutions in drawing up legislation, research activity, collaboration with other laboratories or institutions, technical support and training for operators, pollution environmental monitoring using honey bees and protection of honey bee biodiversity.

Contact person: 
Giovanni Formato