European foulbrood disease is caused by a bacterium Melissoccoccus pluton (formerly called Streptococcus pluton), which invades the mid-gut of four to five-day-old larvae and multiplies rapidly causing death.
Unlike American foulbrood, chalkbrood and sacbrood diseases which affect the larvae in sealed brood cells, European foulbrood disease commonly affects larvae in open brood.
Infected larvae move about inside the cell instead of staying in the normal curled position. Unlike American foulbrood disease, where the larvae consistently slump to the lower side of the cells, larvae infected with European foulbrood appear twisted in different positions.
Infected larvae lose their pearly white sheen, turning creamy white through to yellowish brown and drying into loose brown scales. In severely affected colonies, the capped brood may appear irregular, similar to a failing queen or to American foulbrood disease. However, the brood cappings do not appear dark and sunken as with American foulbrood.
The bacteria may not cause any odour in infected colonies. However, secondary invasion by other bacteria could result in a sour or foul smell. The secondary bacteria that flourish in dying larvae can cause variations in the classic signs of European foulbrood disease.
Once the first signs appear, strong colonies can become non-productive within four weeks and the entire colony may die out if severely affected.
The bacterium M. pluton is a very robust organism. It can survive for months on contaminated equipment.
It usually enters the colony through infected bees, equipment or honey introduced by the beekeeper. The organism can be present in a dormant form for some months before signs are visible.
The infection can spread throughout the apiary during hive manipulation where infected combs are introduced to healthy colonies. Bees drifting from one hive to another and contamination of drinking water are other possible means of spread.
Nurse bees transmit the bacteria during cleaning and feeding, when the mouth parts become contaminated. The organism is then accidentally fed to healthy young larvae, where it finds its way into the mid-gut and multiplies.
European foulbrood disease primarily affects young larvae, killing as many as 90%. Adult bees also can be affected in severe outbreaks.
Because the disease can be present in colonies for months before signs become visible, most hives within the apiary show infection at the same time.
The disease is most likely to be seen in early spring at the first expansion of brood or at the start of a nectar flow. It may also appear at any time after bees have been stressed, such as after moving the apiary.
Diagnosis can only be confirmed in the laboratory by smears taken from infected larvae or a honey test.
In selecting suitable larvae, it is important to select those that are at the initial stage of infection, before collapsing in the cell. Collapsed larvae may be invaded by secondary bacteria, which may prevent accurate diagnosis.
Larvae in the initial stage of infection often turn with their backs facing towards the cell opening, so that the mid-gut is clearly visible.
Closer examination of the infected mid-gut may show that the gut is enlarged and white, instead of the yellow-brown seen in healthy larvae.
European foulbrood disease could possibly be eradicated if it occurred in an isolated area. Eradication may involve the total destruction of all colonies within the affected area.
Should the disease become widespread, eradication may not be possible and it may be necessary to adopt control measures using antibiotics. Antibiotics, combined with good management, have been shown to control but not eradicate the disease.
It is an offence under legislation to feed antibiotics to bees without the written approval of an inspector. It is also an offence to introduce bees, hives and hive products into the state. Penalties apply for both offences.
Hygiene is important in limiting or preventing the spread of the disease. Beekeepers should maintain good apiary hygiene, as follows:
- Avoid the introduction of bees and equipment from unknown sources.
- Avoid exposing honey combs or equipment to robbing. Store and fumigate spare equipment away from robber bees.
- Watch for signs of diseases.
- Report any brood abnormalities immediately by telephone to the Apiary Coordinator on (08) 9368 3154. Brood diseases are notifiable and beekeepers are legally required to report them.
- Submit slide smears and a sample of comb to the Animal Health Laboratories of the Department of Agriculture and Food, Western Australia.
How to submit samples
- Obtain microscope slides from the Apiary Coordinator or the Animal Health Laboratories at South Perth.
- Identify the hive from which the samples are taken.
- Select a piece of affected comb not less than 75mm square.
- Write your name and hive identification number on a clean microscope slide with a permanent marker.
- Select two larvae showing early signs of the suspected disease. Place one at each end of the slide.
- Mash the larvae thoroughly, using a clean match for each larva.
- Remove the bulk of the larval remains from each mashed larva, leaving a separate patch of milky liquid, about the size of a 5 cent coin, at each end of the slide.
- Allow to dry, but protect from the sun at all times.
- Submit five slides, each containing two larvae, for diagnosis.
- Pack the slides to protect them from breakage, and the comb to prevent leakage, and post with completed Report of outbreak of honey bee diseases form to:
Animal Health Laboratories
Department of Agriculture and Food, Western Australia
3 Baron-Hay Court
South Perth WA 6151