CHRONIC BEE PARALYSIS VIRUS (CBPV) By Alan Baxter

Introduction

I wonder how many of you have had stressed colonies succumbing to chronic bee paralysis virus, CBPV, this season? I’ve heard of a couple of beekeepers near me who have had to euthanise a colony. I also had a sick colony this year, probably stressed by the poor foraging weather and queen issues. I also euthanised mine.
Alan Baxter shares his first hand experiences ofCBPV his own blog post with us this week; https://www.alanbaxtersblogs.co.uk/blogs . Alan is a Cornell Master Beekeeper and author of this very useful book on the yellow-legged hornet published by Northern Bee Books  https://www.northernbeebooks.co.uk  Thank you, Alan

Alan’s Blog Post

In June 2023 I was inspecting one of my colonies when I noticed a large number of dead and dying bees on the ground in front of one of the hives.

Fig. 1. dead and dying bees by Alan Baxter

Inside on the top bars the bees were shivering and shaking, unable to fly and not reacting to smoke.

Fig. 2. bees on top bar – video by Alan Baxter

A freshly drawn frames with eggs had other bees looking black and shiny

Fig. 3. frame of comb with CBPV – video by Alan Baxter

Some of the dead and dying bees were being carried away by ants but I didn’t see any significance in that at the time. The signs were classic of chronic bee paralysis virus (CBPV), a disease that has been known for many years and glorified in names such as ‘black robber disease’. But it wasn’t until 1963 that it was identified and named as a virus at the Rothamsted Research Station in England (Bailey & Ball 1963).

What Bailey and Ball also discovered that it was almost certainly the cause of Isle of Wight disease (the Beelistener 2024) that devastated large parts of the honey bee population at the beginning of the last century and for a long time was attributed to acarine or thoracic mite syndrome.

Alarmingly, the Island is only 5 miles from my apiary:

Fig. 4. the Solent and IoW

Here is a brief overview of the disease: It’s caused by a single-stranded RNA virus of the same name that causes paralysis, abnormal behaviour and death. It primarily affects adult honey bees and has been found worldwide in managed and wild bee populations. The virus has been reported in ants, notably Formica rufa, which is commonly found in the south of England, and Camponotus vagus which prefers warmer, drier climes. Ants may act as a reservoir, carrying high viral loads without suffering any of the symptoms. The virus has been detected in Varroa destructor (Seitz et, al. 2019) suggesting the mite may contribute to virus spread, although definitive proof of varroa-mediated transmission remains limited (Celle et, al. 2008).

Fig. 5. Formica rufa – open source

 Fig. 6. Camponotus vagus – open source

Signs

The disease presents in two forms, both of which can be present at the same time:

Type 1 – signs include:

• Large numbers of bees crawling or dead on the ground in front of the hive
• Bees unable to fold their wings —K-wing
• Bees trembling or staggering, unable to fly
• Bees on top of frames, not responding to smoke
• Bloated abdomens with possible signs of dysentery

Fig. 7. Dead and dying bees on ground

Type 2 —Signs include:

• Hairless, oily-looking, almost black workers
• Hairs that have been rubbed off by excessive contact in a crowded hive
• Healthy bees fighting to repel infected bees at the entrance
• Sometimes called ‘black robber disease’.

Fig. 8. CBPV

Nevertheless, it’s the same pathogen, the same disease and the two types usually appear together at the same time

Distribution

A number of studies have established that CBPV is an emerging threat. For example, a long-term survey of colonies in England in collaboration with the National Bee Unit demonstrated a significant increase in reported incidents of the disease.

Incidence and distribution in England and Wales between 2007 and 2017 (G.E. Budge et, al.2020).

Fig. 9. Number of apiaries (per 1000 visits) where chronic bee paralysis was recorded

Fig.10. Sporadic clusters of the disease year on year suggesting disease burn out and reintroduction.

Another study in Italy found increasing spread and a rise in risk levels, but that the incidence was decreasing recently, suggesting adaptation and host-pathogen equilibrium.

Fig. 11. Distribution of Chronic bee paralysis virus (CBPV) in honey bee colonies in Italy (Zavatta et, al. 2024). As far as can be discovered, there are no comparable studies carried out in North America.

Pathogenesis

The disease affects the mushroom bodies and central complex regions of the brain (Ribiere et, al. 2008) and accumulates heavily in the head and nervous tissues.

Fig 12 Honey bee brain

Viral replication occurs in brain regions associated with locomotion and orientation and is strongly neurotropic, explaining symptoms such as trembling, circling, crawling, loss of flight, and paralysis. The progression from infection to death is usually rapid.  Another study found that CBP virus exploits host antimicrobial peptides and alters gut microbiota composition to facilitate viral infection (Yachun Deng et, al. (2024)

Fig. 13. honey bee gut microbiome

Transmission within the colony takes place in the following ways

• Adult bee to bee
• Bees rubbing against each other
• Biting and nibbling
• From the queen’s ovaries

Within and between apiaries

• Pathogen spillover to other species e.g. Bumble bees and to wild colonies
• Robbing and drifting
• Foraging

The virus is not found in brood, comb, honey or pollen (Budge et, al. 2020)

As beekeepers the risk factors we have to consider are:

• Colony overcrowding
• Apiary overcrowding
• Adverse weather conditions
• Stress from parasites
• Poor nutrition – bad weather, monoculture…
• Scale of operation. Budge et al. found that the larger the size of the operation the greater the risk of finding the disease, and those with a history of honey bee imports from other countries also reported more outbreaks than those who sourced their bees in their own country.
• Stress from pesticides (Coulon et, al. 2019)

Management and control methods that can help to alleviate the symptoms and aid recovery are:

• Good husbandry and strict apiary hygiene to prevent further spread
• Remove highly infectious dead and dying bees from the hive floor and the ground outside
• Provide immediate space e.g. super under brood box to separate the unaffected bees from the dead and dying.
• Feed syrup and pollen supplement to compensate for less foraging
• Change comb to provide a healthier environment.
• Euthanize to prevent further spread.

Case study

Returning to my own experience, here are extracts from my notes during the outbreak that occurred in one of my colonies:

Honey producing colony no FH8

2023

• Overwintered colony with 2021 queen (no. 11/21)
• Normal spring build-up
• 10 April —varroa test alcohol wash <2%
• 17 April —given overwintered new queen (no.7/22)
• 30 May — 2 supers of spring honey extracted
• 17 June there were 7 frames of brood 10 seams of bees and 2 supers
• Large number of dead bees on ground covered with ants
• Fighting at the entrance between guard bees and incoming bees with black abdomens

Actions taken

• Moved the whole hive to one side.
• Scrubbed the stand and the ground underneath clean with soda crystals and bleach mixture.
• Moved to another apiary that I use to quarantine swarms.
• On a clean stand and floor, I placed an empty super to keep the brood box clear of the floor and any falling dead or infected bees.
• Fitted an entrance blocker reduced to the smallest space
• Added an extra brood box to give them more space and reduce overcrowding
• Removed for destruction any frames without brood
• Checkerboarded the remaining frames with new frames of drawn comb and foundation.
• Replaced the supers which contained some liquid stores and quite a lot of bees
• Added a feeder with sugar syrup to boost their nutrition (fewer foragers bringing in food)
• Destroyed my gloves, washed my boots with soda crystals and bleach mixture
• Washed my bee suit with soda crystals added to the washing powder.
• Sterilized my hive tool, washed everything in my inspection tool box and cleaned my smoker, especially the bellows.
• Fed sugar syrup and pollen supplement to stimulate the production of winter bees.
• 30 July 24 kg honey not extracted, left tor bees
• Varroa test with alcohol-wash 4%, treated with MAQS (Mite Away Quick Strips-formic acid)

The colony appeared to recover and was routinely treated with oxalic acid by GasVap on 2 December 2023.

2024

• 2 April –tested for varroa – < 3%
• 11 May- Bailey comb change (complete change of all comb)
• 30 July – tested for varroa – 3%
• Removed 4 supers for extraction, left 2 for bees
• Treated for varroa with Formic Pro
• 1 September- tested for nosema – negative
• 8 September- stimulative feeding for queen to lay winter bees*
• 30 September – 7 seams of bees + 4 frames capped stores + 1 full super
• 7 December – treated for varroa – Oxalic Acid by GasVap

Everything seemed to be well and I was confident that the colony had recovered.

But now we come to 2025. In April, I noticed the spring build-up was slow compared to other similar colonies, so I tested for nosema, which was negative. I did a varroa count by CO₂ which found 6 mites in 300 bees.

In case the queen was failing I gave them a new overwintered queen. Then on 2 May I saw dead bees on ground & on hive floor, bees fighting at entrance, bees in brood box shivering and crawling on top of frames. There was no queen to be seen, and a single supersedure cell was found.

I was faced with a number of options, none of which were appealing to say the least.

Decision points

I could treat the colony as in 2023 but add an extra brood chamber with separate entrance to keep the healthy bees away from the sick and dying.

This would offer a slight chance of success if taken quickly, but no guarantee of longer-term recovery.

It would carry the risk of infecting other colonies by drifting, robbing, foragers on flowers and drones mating.  Which left the nuclear option of euthanizing the colony for the greater good of mine and other beekeepers’ apiaries, and any free-living colonies in the area. And this is what I decided to do.

I confess that it was a very hard decision to take, and I sincerely hope I never have to do it again.

To sum up

CBPV is a highly infectious disease of the nervous system of insects (not just honey bees). In particular it:

• Rapidly devastates colonies and spreads to and between entire apiaries
• Transmitted by direct contact, in trophallaxis, nibbling and orally in faeces
• Passed to other colonies and apiaries through drifting, robbing, mating and foraging
• May be transmitted by other carriers such as ants and, possibly, by varroa
• Affects workers, queen and drones
• Dead and dying bees are still highly infectious
• Management and control can mitigate at a low level of infection but there is no guarantee of recovery
• Euthanasia may be necessary for severe infections and to protect other colonies

Final thought on euthanasia

There is something about the superorganism that we call a honey bee colony that seems to be so much greater than the sum of its parts.

Killing It felt like destroying an ‘intelligence’, a society of sentient beings, with a finely tuned structure in which every member acts entirely for the benefit of the whole and never in the interest of the individual.

Can’t we so-called civilized humans learn lessons from that!

Footnotes 2026

Since writing this case study I’ve learnt a number of important lessons:

• It’s a pollen dearth that stimulates queens to lay winter bees (Mattila & Otis 2007).
• Only nurse bees consume pollen efficiently (Crailsheim et, al. 1992).
• Nurse bees are spatially concentrated in the brood nest and show limited movement away from their brood care zone.
• Protein supplements are mainly eaten by bees older than 14 days.
• Pollen supplements placed on the top bars of brood frames are not consumed by the nurse bees for which they are intended (Kleckner et, al. 2026)
• The composition of pollen is complex and variable, for example; pollen supplements are deficient in many key complex nutrients, see diagram above.
• Although supplements stimulate brood production, the nurse bees have to raid their pollen stores to make up the shortfall potentially leading to winter malnutrition and larval cannibalism (Schmickel & Crailsheim 2002). 
• I was doing them no favours with early autumn stimulative feeding!  
• Nevertheless, it’s the same pathogen, the same disease and the two types usually appear together at the same time