Chronic bee paralysis

Chronic bee paralysis is a viral disease of adult bees. It shows up as bees trembling and crawling in front of the hive, or as black, shiny, hairless bees harassed by their nestmates. In severe cases, a carpet of dead and dying bees builds up at the entrance within a few days. It often strikes strong, populous colonies.

Long regarded as a sporadic disease, it is now increasing in several countries. A study in England and Wales showed a very rapid rise in cases over a decade, with a higher risk in large operations². There is no medicine: control relies on colony management and on how apiaries are organised.

Chronic bee paralysis virus

A virus apart

Chronic bee paralysis virus (CBPV) is a positive-sense, single-stranded RNA virus. Its genome consists of two main segments, called RNA 1 and RNA 2, of roughly 3,700 and 2,300 nucleotides⁴. Its particles are ellipsoid and variable in size, whereas most honey bee viruses are spherical¹.

Its place in virus classification is still open. CBPV shares some features with two virus families, the Nodaviridae and the Tombusviridae, but differs enough for researchers to regard it as the first member of a new family, which has not yet been formally recognised^{4, 5}. Despite the similar names, it is therefore not closely related to acute bee paralysis virus¹.

Where it multiplies

The virus multiplies notably in the bee’s nervous system, which explains the trembling and paralysis. Sick bees carry huge amounts of virus, in the order of billions of genome copies or more¹. Conversely, many healthy colonies carry the virus at low levels; disease appears when favourable conditions let it multiply¹¹.

How the virus spreads

Through contact, across the cuticle

The main route is direct contact between bees. When the cuticle is damaged, for example by hair loss or small wounds, virus from a sick bee enters a healthy bee more easily¹. The more tightly packed the bees, the more of these exchanges occur: hence the link with overcrowding.

Anything that wears the cuticle raises the risk, notably pollen traps and varroa¹¹. Fitting pollen traps is even known to be able to trigger symptoms².

Through faeces

The faeces of sick bees contain infectious virus. Healthy bees exposed to these faeces alone became infected³. In a hive confined by bad weather, this route becomes more important.

Other possible routes

The virus, in its replicating form, has been detected in ants and varroa mites from affected apiaries⁶. The real role of these hosts in spread remains poorly understood. Transmission from the queen to her offspring is also suspected^{2, 11}. Between colonies, drifting, robbing and swapping combs covered with bees spread the virus.

Why the disease is increasing

An emerging disease

A study published in 2020 analysed bee health inspection data from England and Wales. The number of cases rose exponentially between 2007 and 2017: reported in a single county in 2007, the disease was present in the great majority of counties ten years later². Cases were clustered in space, suggesting local spread between neighbouring apiaries.

The role of operation size and density

The study found a higher risk among professional beekeepers, whose apiaries held on average many more colonies than those of hobbyists². The authors attribute this to colony density and to certain management practices, without testing them one by one. A higher risk was also seen among beekeepers who had imported bees in the previous two years.

Confinement and climate

Outbreaks often follow a period when bees are kept indoors: prolonged rain, a spring cold snap, lack of forage, long-distance migratory moves^{10, 11}. Conifer honeydew is also cited as a contributing factor¹¹. However, an analysis of English data found no link between the spread of the disease and temperature, rainfall or wind: its emergence appears to have another cause⁹.

Impact on the colony

A bee that shows symptoms usually dies within a week². In an affected colony, thousands of adults are lost this way and the honey crop is compromised. Some colonies collapse; others recover when conditions improve.

The course of the disease often lasts several weeks, sometimes several months¹¹. It mainly affects workers, but all three adult castes can be infected.

Recognising chronic bee paralysis

Trembling form (type 1)

• Bees with abnormal trembling of the wings and body.
• Unable to fly: bees crawl on the landing board and in the grass, sometimes in clusters.
• Swollen abdomen, wings spread and apparently dislocated.

Black form (type 2)

• Hairless bees, black, shiny, almost greasy-looking.
• Slightly smaller bees, harassed and nibbled by nestmates, pushed away by guards at the entrance.
• At first they can still fly; they then become flightless, tremble and die within a few days^{1, 11}.

Both forms can occur together in the same colony or separately.

The carpet of bees outside the hive

In severe cases, dead bees pile up at the entrance, sometimes several centimetres deep¹⁰. This carpet is concentrated in front of the affected colonies, not scattered across the apiary. The bodies are of different ages, because the deaths are spread over time¹¹.

Do not confuse with

The symptoms overlap with those of other disorders: in the apiary, you reason from several signs together, but only a laboratory test can confirm¹⁰.

Poisoning is the most common confusion and the one with the heaviest consequences. Mortality affecting several colonies at once, with fresh bodies spread across the whole apiary, should make you think of a pesticide^{10, 11}. The two causes can also combine: some pesticides can worsen an existing infection¹¹.

Diagnosis

In the apiary

1. Observe: type of symptoms, number of hives affected, distribution of dead bees.
2. Note the conditions of the previous days: weather, agricultural spraying, hive manipulations, pollen traps.
3. Collect bees showing symptoms and freshly dead bees, from inside and in front of the hive. A French bee health fact sheet recommends at least twenty or so bees¹¹.
4. Keep the sample cold and labelled, and ask the laboratory about shipping conditions.
5. If poisoning is possible, alert the authorities without delay, so that samples can be used in the investigation.

Quantitative PCR testing

The reference method is real-time quantitative PCR after reverse transcription (RT-qPCR). It measures the amount of viral genome per bee⁷. The mere presence of the virus proves nothing: it is the viral load that matters.

A European inter-laboratory study states that symptoms are usually associated with loads above 10⁸ genome copies per bee, the threshold used by the European Union Reference Laboratory for Bee Health. Loads above 10⁶ copies per bee may be considered probable cases⁸. A high load does not, however, rule out an associated poisoning.

In France, testing is carried out by approved laboratories; the cost is usually borne by the beekeeper, unless the test is part of a surveillance scheme that covers it^{11, 12}.

Regulations

In France, chronic bee paralysis has no regulatory status: it is not a notifiable disease¹¹. However, sudden mass mortality of adult bees, especially if poisoning is possible, falls under a state surveillance scheme: it should be reported promptly to the departmental animal health authority (DDPP). In the regions where it operates, the bee mortality and weakening observatory (OMAA) offers a single point of contact to report such problems, with free investigations and tests when the case is eligible¹².

Rules vary from country to country.

What to do: prevention and management

There is no treatment

No medicine works against CBPV¹¹. Action focuses on the colony, the apiary and management practices.

For an affected colony

• Give space: add a super or frames to loosen up the bees.
• Remove the sick bees: a method considered promising involves caging the queen, moving the hive at least fifty metres or so, shaking the bees into the air, then putting the hive back in place. Only bees able to fly return; the operation can be repeated about six days later. Its effectiveness has not been demonstrated in rigorous trials¹⁰.
• Requeen affected or relapsing colonies, preferably with a queen from a less susceptible stock¹¹. Evidence is limited: part of the benefit may come from the brood break caused by the change¹⁰.
• Do not move frames covered with bees from a sick colony to a healthy one.
• Remove pollen traps from affected colonies.
• Cull the most severely affected colonies, which keep the virus going in the apiary¹¹.

At apiary level

• Match colony numbers to forage and avoid high densities^{2, 11}.
• Space hives out and vary their orientation or landmarks to limit drifting.
• Prevent overcrowding: add space in time, especially before and during a strong flow.
• Limit prolonged confinement: avoid long migratory moves and do not shut colonies in longer than necessary.
• Control varroa, which damages the cuticle and weakens bees.
• Be cautious with introductions of outside bees, and watch new colonies for a few weeks before mixing them with the others².
• Apply the general rules of apiary biosecurity and good beekeeping practice¹³.

The most common mistakes

• Concluding it is poisoning without a test, or ruling out poisoning without checking: only a test settles it.
• Sampling too late or keeping bees warm: the sample becomes unusable.
• Boosting a healthy colony with frames from a sick one, which carries the virus.
• Moving the sick colony to another apiary, risking contamination of a new site.
• Leaving pollen traps on a colony with symptoms.
• Concentrating too many colonies on one site.

Frequently asked questions

Is honey from an affected colony safe to eat? Yes. CBPV is a bee virus; it poses no danger to humans.

Can an affected colony recover? Yes, often, when conditions improve. But it may relapse: follow-up over several weeks is needed.

Does varroa transmit chronic bee paralysis? The virus has been detected in varroa mites, but transmission occurs mainly through contact between bees and through faeces^{3, 6}. Varroa acts rather as an aggravating factor, damaging the cuticle and weakening bees. It is acute bee paralysis that is closely tied to varroa.

Should the hive be disinfected after an outbreak? It is sensible to clean the floor covered in dead bees and any equipment soiled with faeces before reusing it. See the disinfecting equipment page.

References

1. Ribière M., Olivier V., Blanchard P. (2010). Chronic bee paralysis: a disease and a virus like no other? Journal of Invertebrate Pathology 103 (Suppl. 1): S120-S131. doi.org
2. Budge G.E., Simcock N.K., Holder P.J., Shirley M.D.F., Brown M.A., Van Weymers P.S.M., Evans D.J., Rushton S.P. (2020). Chronic bee paralysis as a serious emerging threat to honey bees. Nature Communications 11: 2164. doi.org
3. Ribière M., Lallemand P., Iscache A.L., Schurr F., Celle O., Blanchard P., Olivier V., Faucon J.P. (2007). Spread of infectious chronic bee paralysis virus by honeybee (Apis mellifera L.) feces. Applied and Environmental Microbiology 73(23): 7711-7716. doi.org
4. Olivier V., Blanchard P., Chaouch S., Lallemand P., Schurr F., Celle O., Dubois E., Tordo N., Thiéry R., Houlgatte R., Ribière M. (2008). Molecular characterisation and phylogenetic analysis of Chronic bee paralysis virus, a honey bee virus. Virus Research 132(1-2): 59-68. doi.org
5. Chevin A., Coutard B., Blanchard P., Dabert-Gay A.S., Ribière-Chabert M., Thiéry R. (2015). Characterisation of structural proteins from Chronic Bee Paralysis Virus (CBPV) using mass spectrometry. Viruses 7(6): 3329-3344. doi.org
6. Celle O., Blanchard P., Olivier V., Schurr F., Cougoule N., Faucon J.P., Ribière M. (2008). Detection of Chronic bee paralysis virus (CBPV) genome and its replicative RNA form in various hosts and possible ways of spread. Virus Research 133(2): 280-284. doi.org
7. Blanchard P., Ribière M., Celle O., Lallemand P., Schurr F., Olivier V., Iscache A.L., Faucon J.P. (2007). Evaluation of a real-time two-step RT-PCR assay for quantitation of Chronic bee paralysis virus (CBPV) genome in experimentally-infected bee tissues and in life stages of a symptomatic colony. Journal of Virological Methods 141(1): 7-13. doi.org
8. Schurr F., Cougoule N., Rivière M.-P., Ribière-Chabert M., Achour H. et al., Dubois E. (2017). Trueness and precision of the real-time RT-PCR method for quantifying the chronic bee paralysis virus genome in bee homogenates evaluated by a comparative inter-laboratory study. Journal of Virological Methods 248: 217-225. doi.org
9. Rowland B.W., Rushton S.P., Shirley M.D.F., Brown M.A., Budge G.E. (2021). Identifying the climatic drivers of honey bee disease in England and Wales. Scientific Reports 11: 21953. doi.org
10. Budge G., Stainton K. (2016). Chronic bee paralysis. Bee Craft, September 2016 (article distributed by the National Bee Unit). nationalbeeunit.com
11. FNOSAD (2014). Fiche n° 4 : la paralysie chronique (French bee health fact sheet, supported by FranceAgriMer and the European Union). apiservices.biz
12. Réussir Apiculture. L'OMAA, un système de surveillance pour déclarer et recenser les troubles de santé des abeilles (in French). reussir.fr
13. FAO, IZSLT, Apimondia, CAAS (2021). Good beekeeping practices for sustainable apiculture. FAO Animal Production and Health Guidelines No. 25.
14. USGS Bee Inventory and Monitoring Lab. Apis mellifera, worker in side view (public domain). usgs.gov

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