Foulbrood: how to spot and report the disease

Foulbrood is a notifiable disease of honey bees. There are two different types of foulbrood.

American foulbrood

American foulbrood (AFB) is caused by a spore-forming bacterium called Paenibacillus larvae.

The purpose of the spores is to allow the bacterium to survive in the absence of the host. The spores are highly resistant to extremes of temperature, chemical attack and other adverse conditions that kill most bacteria. This means that it is difficult to eliminate the bacterium from infected colonies. Spores can remain viable for many years on contaminated equipment, and the bacterium will germinate and reproduce when it comes back into contact with a honey bee larva.

Spores are accidentally fed to a larva by nurse bees in the form of contaminated brood food. The bacteria kill the bee larva by completely consuming the body tissues. This occurs only after the cell has been sealed.

European foulbrood

European foulbrood (EFB) is caused by the bacterium Melissococcus plutonius. This is not a spore forming bacterium.

Like AFB, the bacterium is accidentally fed to a larva by nurse bees in the form of contaminated brood food. It multiplies in the mid-gut and causes the bee larva to starve to death by competing for its food. This normally occurs shortly before their cells are due to be sealed. The bacterium remains in the gut and does not invade the body tissues of the larva.

Symptoms of this disease are most commonly seen when there is a shortage of nectar, pollen or supplementary feed for bees. Other stress factors such as infestation with Varroa mites (which can be controlled) may also lead to an increase in symptoms. 

Clinical signs - AFB

This disease affects sealed brood and has characteristic disease signs, which may include the following:

• uneven 'pepper-pot' brood pattern
• darkened, sunken, greasy cell cappings
• performated cell cappings 
• sticky larval remains which can be drawn out with a matchstick('ropiness test')
• hard, dark scales which are difficult to remove from cells

Clinical signs - EFB

This is primarily a disease of the unsealed brood and symptoms typically include:

• erratic or uneven brood pattern
• twisted larvae lying unnaturally in the cell
• discoloured larvae
• larvae which has a melted appearance (no segmentation)
• an unpleaseant sour smell

How foulbrood is spread

EFB can be spread by the beekeeper's protection (e.g. gloves) and tools (e.g. hive tool, smoker, drone fork) during transfer of combs and brood from an infected hive to a healthy one.

The disease can also be transmitted by robbing (the act of bees stealing honey/nectar from the other colonies; also applied to bees cleaning out wet supers or cappings left uncovered by beekeepers) and swarms (a collection of bees, containing at least one queen that split apart from the mother colony to establish a new one; a natural method of propagation of honey bees).

Infection zones

In Scotland there is a defined 'Infection zone'. Businesses within the infection zone are allowed to sign up to the European Foulbrood Control Plan which allows them to self-certify their inspections and sample for foulbrood diseases allowing a greater flexibility on the movement of apiaries for the survival of commercial businesses without putting the spread of notifiable diseases at risk within Scotland. 

Human health implications

There are no human health implications because the disease is not zoonotic.

Legislation

The Bee Diseases and Pests Control (Scotland) Order 2007

Biosecurity

Beekeepers are encouraged to undertake heightened vigilance, good biosecurity measures and hygiene procedures, as these are two key actions that beekeepers can take to help control this disease. Useful information is available to beekeepers on the SBA website and BeeBase.

Limiting the spread of bee disease

Environment Minister, Gillian Martin has written to Scotland's beekeepers to remind them of action which can and should be taken to help maintain the health and wellbeing of honeybees.

See: Letter from Environment Minister to beekeepers: August 2023. (Rural Payments website)

Our Honey Bee Health Team have produced a heatmap which shows the current understanding of the distribution of EFB in Scotland. Inspection records on BeeBase were used to map areas where there have been confirmed cases of EFB from 2021 to 2023.