Kashmir Bee Virus (KBV)

Kashmir bee virus (KBV) belongs to the same group as acute bee paralysis virus (ABPV) and Israeli acute paralysis virus (IAPV) and is usually carried without symptoms. It becomes active when the varroa load rises; by killing adult bees and brood within a short time it can weaken the colony rapidly. In the field it cannot be told apart from the other paralysis viruses; there is no medicine, and the thing to do is bring varroa down immediately.

What is it?

KBV was first described in the 1970s in samples of the Asian honey bee (Apis cerana) from the Kashmir region, which gave it its name. It was later detected in the western honey bee (Apis mellifera) in many parts of the world.

ABPV, KBV and IAPV are closely related viruses and most sources treat them together as the "acute paralysis viruses". Their symptoms are the same; which one is responsible can only be determined in the laboratory. For the beekeeper the upshot is this: the question "Is this KBV or ABPV?" cannot be answered in the field, but what needs to be done is the same anyway.

How does it spread, and why is varroa decisive?

The virus circulates in the colony through food sharing, royal jelly and faeces, and from the queen to the egg; as long as it stays on these routes it usually causes no symptoms.

What changes the situation is varroa. While feeding, the mite injects the virus directly into the bee's haemolymph. When introduced into the haemolymph under experimental conditions, KBV is known as one of the most lethal bee viruses, killing the bee within a few days even in very small amounts. This is why KBV-related losses are almost always seen together with a high mite load.

How to recognise it

There is no symptom specific to KBV that can be told apart by eye. When it becomes active, you may see:

• Trembling, uncoordinated adult bees unable to fly
• Dead bees rapidly accumulating in front of the hive and on the floor
• Perforated cappings, a patchy brood pattern, dead larvae and pupae in the cells
• Often a rapidly shrinking bee population without any obvious symptom; a colony collapsing especially in late summer and autumn

With the acute paralysis viruses the bees' hair and wings are normal; this distinguishes them from chronic bee paralysis (hairless, shiny black bees) and deformed wing virus (crumpled wings).

How it differs from similar conditions

How to confirm it in the hive

• Do a varroa count: the mite rate on adult bees with the icing sugar roll or alcohol wash, or the daily mite drop with a drop board. A high count largely explains the picture.
• Examine the brood area: perforated cappings and dead pupae support varroa damage.
• The type of virus can only be determined in the laboratory by PCR; in most cases this does not change management, but it is useful for research or in heavy losses.

What to do

1. Bring varroa down immediately. Use an authorised product (from the oxalic acid, formic acid, thymol or amitraz group) according to its label and in a way that does not clash with the honey harvest. Take the product and dose from the package leaflet or from your veterinarian.
2. Support the colony. If stores are short, give syrup or fondant; if pollen is insufficient, supplement it.
3. Unite a badly weakened colony. Uniting it with a healthy colony whose varroa has been brought down is better than letting it collapse and be robbed.
4. Limit the spread. Do not move frames or bees from a diseased colony; reduce the entrances to prevent robbing; close up and remove a dead-out hive immediately.
5. Requeen. In a recovering colony a young, healthy queen speeds up development.

Prevention

• Measure varroa regularly from spring to autumn; keep it low especially before the winter bees are raised.
• Treating at the same time as neighbouring apiaries reduces reinfestation.
• Do not buy colonies, package bees or queens from unknown sources.
• Keep colonies strong and well fed; replace old combs regularly.