European Foulbrood

European foulbrood (EFB), caused by the bacterium Melissococcus plutonius, is a brood disease that usually kills larvae before their cells are capped. It generally appears in spring and during periods of stress; in mild cases the colony can recover, in severe cases it dwindles. As in many countries, it is notifiable in Türkiye.

What is it and how does it develop?

The bacterium is taken in with the larva's food and multiplies in the midgut; it competes with the larva for its food and the larva starves to death. Death is mostly seen in 4–5-day-old open larvae lying curled in their cells. Secondary bacteria multiplying in the dead larvae produce the sour smell typical of the disease and the melted appearance of the larva.

Unlike American foulbrood, the agent does not form spores; however, it can survive for months in comb and in honey and faecal residues. There may also be carrier colonies without symptoms. The infection spreads through exchanging combs and frames, robbing, buying and selling colonies and dirty tools.

The disease often breaks out under stress: a cold, wet spring, a shortage of nectar and pollen, too few nurse bees, rapid brood expansion and frequent moving.

How to recognise it

• Death in open brood: Larvae die before their cells are capped; damage in capped brood is less common.
• Colour: The pearly white larva turns first yellowish and then brown.
• Position: The larva loses its normal "C" curl; it looks twisted, shifted sideways or upwards, or collapsed as if melted into the bottom of the cell.
• Internal structure: The breathing tubes (tracheae) of the dead larva can be made out as white lines; the gut contents look creamy white.
• Brood pattern: Scattered, patchy brood; larvae of different ages are mixed together.
• Scale: The dried remains form a rubbery, dark brown scale that comes out of the cell easily.
• Smell: A sourish, sometimes vinegary smell.

How it differs from American foulbrood

In some EFB cases larvae may also die under the capping and the cappings may sink; the field picture then becomes confused with AFB. Both diseases can also occur together in the same colony.

How to confirm it at the hive

• Carry out a matchstick test on suspect open larvae; they should not rope. If they do rope, give priority to the possibility of AFB.
• Look at the colour and position of the larvae and at whether the scale sticks to the cell.
• A definitive diagnosis is made in the laboratory from a larval sample. There are rapid field kits that distinguish EFB from AFB; a positive result also requires official notification.

What to do, step by step

1. Isolate the hive: Until the diagnosis is clear, do not move frames, bees, honey or tools from this hive; do not unite or sell it.
2. Report it: Notify the official veterinary service / local agriculture authority; an official veterinarian decides on sampling and on the measures to be taken.
3. Prevent robbing: Reduce the entrance and do not leave honey or comb exposed.
4. Clean your tools: Clean the hive tool and gloves between hives, and leave the suspect hive until last.
5. Reduce stress: Within the framework of the official instructions, strengthen the colony: sufficient food and pollen, space matched to the strength of the colony, and a young queen if necessary.

In severe cases the authority may recommend the shook swarm method: the bees are shaken into a new hive with foundation and the old combs are destroyed. In very severe or recurring cases, destruction of the hive may be ordered.

Treatment and medicine information

Do not use antibiotics on your own initiative. Antibiotics suppress the symptoms, hide the problem and leave residues in honey; their use in bees is not permitted in Türkiye or in the EU. In mild cases, strengthening the colony and replacing soiled combs is often enough; but make this decision together with the official veterinarian as well.

Prevention

• Renew combs regularly; old combs harbour the agent.
• Do not buy colonies, swarms or combs of unknown origin.
• Keep colonies strong and well fed; in spring avoid expanding beyond the strength of the colony.
• During frequent moves and long dearth periods, check the brood nest more often.