More than twenty viruses have been identified in honey bees. Most are present in colonies without symptoms and turn into disease only when the balance is upset.

What matters for the beekeeper is not knowing each virus but knowing what conditions make them active.

What Varroa changed

Viruses existed before Varroa. They spread by mouth and with food, and stayed at low levels.

Varroa changed two things:

• Direct transmission: As the mite feeds it injects the virus into the haemolymph; the barriers of the digestive tract are bypassed
• Increased load: The viral titre jumps from a symptomless level to a disease level

Virus problems today are therefore largely Varroa problems.

The main groups

Deformed Wing Virus

The most widespread and most destructive. It produces crumpled wings, a shortened abdomen and a very short life. Its real damage is done without symptoms: a normal-looking winter bee dies early.

Paralysis viruses

Acute Bee Paralysis Virus, Kashmir Bee Virus and Israeli Acute Paralysis Virus are closely related. They cannot be told apart in the field; distinction is possible only in the laboratory.

They are usually silent. When activated they can kill adults and brood within a short time.

Chronic Bee Paralysis

It produces a different picture from the others and is treated separately: trembling, loss of hair and a shiny appearance.

Black Queen Cell Virus

It affects queen brood; the cells darken. Important for beekeepers rearing queens. It is reported to occur together with nosema.

Sacbrood

It turns the larva into a fluid-filled sac. It usually regresses on its own.

Others

Agents such as filamentous virus, Apis iridescent virus, Kakugo and Arkansas viruses have been identified. They cannot be diagnosed in the field and the economic importance of most is limited.

Common signs

• Deformed wings, undeveloped bodies
• Bees crawling, unable to fly
• Trembling and loss of coordination
• Patchy brood, dead brood
• Unexplained dwindling

The signs overlap; telling which virus is involved is not possible in the field and is not necessary.

What to do

There is no treatment acting directly on viruses. What can be done is indirect but effective:

• Keep Varroa under control. This is the single most important measure
• Keep nutrition strong. Varied pollen increases resistance
• Attend to equipment hygiene
• Do not buy colonies from unknown sources
• Requeen. A weakened colony recovers with a young queen
• Work with lines showing strong hygienic behaviour

Summary

Learning virus names gains the beekeeper little. Keeping the mite load low manages them all at once.