Chronic Bee Paralysis Virus

Chronic bee paralysis is a disease of adult bees caused by chronic bee paralysis virus (CBPV). Trembling, flightless bees and bees that have lost their hair and look shiny black and greasy are typical; in severe cases heaps of dead bees accumulate in front of the hive. There is no medicine for the virus; the essentials are to reduce crowding and transmission and, if necessary, to requeen.

What is it and how is it transmitted?

CBPV is a virus unlike most other bee viruses and is one of the few viral diseases that can be recognised in the field. The main route of transmission is close contact between bees: in a crowded hive the bees' hairs are broken as they rub against one another, and the virus enters through tiny wounds. The faeces of sick bees also carry the virus; contaminated comb and food keep the transmission going.

The disease appears more often in the following situations:

• Bees crammed into the hive during long periods of bad weather
• Very populous colonies with insufficient space
• After a strong nectar flow or after moving
• Large, dense apiaries where many hives are kept together

Varroa can carry this virus, but it does not play as decisive a role as it does with deformed wing virus. Genetic differences in colonies' susceptibility have been reported.

How to recognise it

The disease appears in two forms; both can be seen in the same colony, or even one after the other in the same bee.

1. The trembling form

• Bees with trembling wings and bodies
• Bees unable to fly, crawling in front of the hive, on grass and on the top bars
• A swollen abdomen caused by the honey stomach filling with fluid
• Wings held apart and askew
• Sick bees gathering in clusters on the top bars or at the entrance

2. The shiny black form

• Black bees that have lost their hair and look shiny and greasy; the abdomen may look smaller than normal
• Guard bees nibbling at these bees and refusing to let them in at the entrance
• Death within a few days

Shiny, hairless bees moving among healthy bees and being chased away by the guards is the most recognisable picture of this disease.

How it differs from similar conditions

How to confirm it at the hive

• Examine the front of the hive, the entrance and the top bars: trembling and shiny black bees seen together are a strong indication for a field diagnosis.
• Monitor the number of dead bees in front of the hive for a few days; if it is increasing, the disease is progressing.
• Do a varroa count at the same time; do not overlook accompanying problems.
• A definitive diagnosis is made in the laboratory by PCR. Send live or freshly dead sick bees in a closed container.

What to do

There is no medicine for the virus. The aim is to reduce transmission and help the colony recover.

1. Give space and reduce crowding. Add a box; consider splitting overcrowded colonies.
2. Improve ventilation.
3. Clear away dead bees. Remove the bees accumulating in front of the hive and on the floor and bury or burn them.
4. Do not transfer bees, frames or comb from the sick colony to another hive; do not unite the sick colony with a healthy one.
5. Avoid unnecessary interventions. Opening and closing the hive often increases stress and crowding.
6. If it recurs, requeen. A queen from a different, healthy line may reduce the colony's susceptibility.
7. Renew combs soiled with faeces. Once the disease has passed, take old, soiled combs out of circulation.

Prevention

• Give colonies space in good time and prevent crowding.
• Keep the number and density of hives in the apiary reasonable.
• Do not buy colonies, package bees or frames from unknown sources.
• Rear queens from colonies that show no problems.
• Keep varroa low; this maintains the colony's overall resistance.