Israeli Acute Paralysis Virus

Israeli acute paralysis virus (IAPV) is an RNA virus that can cause wing trembling, paralysis and mass deaths in front of the hive in adult bees. On its own it usually stays silent; it does its real damage together with the varroa mite. No definitive diagnosis can be made at the hive: the beekeeper's job is to keep varroa low and, if the picture is suspicious, to send a sample to the laboratory.

What is it?

IAPV is closely related to acute bee paralysis virus (ABPV) and Kashmir bee virus (KBV). Together these three viruses are called the "acute paralysis group"; their symptoms and transmission routes are largely the same. It gets its name from being first described in Israel, from bees showing signs of paralysis; today it is found in many parts of the world.

In the USA in 2007 a statistical association with colony collapse disorder (CCD) was reported. Later studies showed that IAPV was not the sole cause of the collapses, but one of several factors acting together with varroa, nutritional stress and other diseases.

The virus can also be present at low levels, without symptoms, in healthy-looking colonies. It multiplies rapidly when the varroa load rises, when the colony goes hungry or when it is weakened by another disease.

How does it spread?

• Varroa: The most important route. The mite injects the virus directly into the bee's blood (haemolymph); virus transmitted this way is far more lethal.
• Orally: Food sharing between bees, secretions of nurse bees, contaminated honey and pollen.
• From queen to brood: The virus can also pass through the egg.
• Between colonies: Robbing, drifting bees, moving frames and bees, and package bees and queens brought in from outside.

The virus has also been detected in other bees such as bumblebees; the possibility of transmission via flowers is being investigated.

How to recognise it

The symptoms are in adult bees, not in the brood:

• Bees trembling their wings and walking with jerky movements
• Bees unable to fly, crawling in front of the hive and in the grass, turning on their backs and struggling
• Progressive paralysis and death within a short time; most of the dead pile up right in front of the hive
• The colony weakening quickly; the number of bees on the frames stays low relative to the amount of brood
• Usually appears in late summer and autumn, when varroa levels are high

How it differs from similar conditions

How to confirm it in the hive

Appearance alone is not enough; the viruses of the acute paralysis group can only be told apart in the laboratory (by molecular testing). What to do in the field:

1. Measure the varroa level. Use an alcohol or icing sugar wash, or a counting board placed under a mesh floor. If signs of paralysis and high varroa occur together, the suspicion is strong.
2. Rule out poisoning. Find out about spraying in the area; if there is sudden death in several hives, keep a sample of dead bees and report the case.
3. Send a sample to the laboratory. Take a sample of live bees showing symptoms into a clean container. Ask the official veterinary service / local agriculture authority how the sample should be stored (usually chilled or frozen) and which laboratory it should go to.

What to do

1. Mark the colony and keep it separate. Do not give frames, bees or honey from this hive to other hives; do not make splits from it.
2. Bring varroa under control. If the count is high, treat with an authorised varroa medicine, following the label instructions.
3. Reduce stress. Feed syrup during a nectar dearth and a protein supplement when pollen is short; do not open the hive more often than necessary.
4. Prevent robbing. Reduce the entrance; if a weakening colony is robbed, the virus is carried to neighbouring hives.
5. Do not unite a diseased colony with a healthy one. Wait until the deaths stop and varroa has been brought down.
6. If the problem persists, requeen. Prefer lines with strong hygienic behaviour, selected for varroa resistance.
7. Do not distribute the combs of a collapsed colony. Melt down old brood combs; do not reuse the hive before cleaning and drying it.

Treatment and medicines

There is no authorised medicine against IAPV or any other bee virus. Antibiotics have no effect on viruses and moreover leave residues in honey. Do not trust products sold with the claim that they "destroy the virus"; research on RNA-based methods is at the experimental stage.

The core of treatment is varroa control. Authorised active substance groups include organic acids (oxalic acid, formic acid), essential oil components such as thymol, and synthetic acaricides. During the honey flow and with honey supers on the hive, do not use medicines that are not compatible with the honey harvest; using the same active substance year after year leads to resistance in the mite.

Prevention

• Do varroa counts several times a year (spring, midsummer, late summer, autumn) and treat in good time when the threshold is exceeded.
• Protect the late-summer period, when the winter bees are raised, in particular; high varroa at this time comes back as paralysis and losses in winter.
• Keep colonies strong and well fed; unite weak colonies in good time.
• When buying bees, queens and frames, prefer sources whose health status is known.
• Do not place hives too close together in a single row; reduce drifting with colours and markings.