European Foulbrood (EFB)

European Foulbrood (EFB) used to be quite rare in Ireland but it reared its ugly head a couple of years ago when it was discovered in hives at the annual Beekeeping Course at Gormanston so it’s out there and you need to be aware of it!

Life Cycle

European Foulbrood (EFB) is caused by the non-sporulating bacteria Melissococcus plutonius (Morton). It is the nurse bee who feeds bacteria to the innocent larvae in brood food. Once inside a larva the bacteria feed on the gut contents and rapidly proliferate and soon fill the gut, although unlike American Foulbrood it does not breach the gut wall to invade the body cavity in any way. If a larva is well fed it can feed both its load of M.plutonius and itself well enough for it to metamorphose successfully to an adult. If, on the other hand, the larva does not get enough food for both, then the bacteria will take precedence over available food and the larva will starve to death. That is when the beekeeper will discover it, in times of poor weather and shortage of pollen, otherwise it can lurk.

The gut of the honey bee larva is a blind sac until it reaches the pro-pupal stage when the gut breaks though to void the gut contents into the cell. If a larva reaches this stage of development with its load of M.plutonius, then they exit at this point and the larva goes on to pupate and become an adult honey bee. When the adult emerges from the cell, it leaves a contaminated cell behind it and the next larval occupant will become infected and so on and so forth. If, on the other hand, the larva starves to death it does so before it reaches the pro-pupal stage and does not void its stomach contents (including the infectious load of M.plutonius) and its little carcass is unceremoniously, but harmlessly, dumped outside the hive.

If there is plenty of forage in the early summer the disease can go undetected by the beekeeper. Later in the year when the queen is laying full throttle and the colony is stretched, if the amount of available forage should suddenly fall, then the number of larval deaths may rise to such a level that the house bees are unable to clear them out quickly enough. At this point the dead may accumulate and the disease may then become noticeable but even then perhaps only for a short while.

Recognition
  • The larvae generally die just before the cells are due to be sealed. Unlike healthy larvae at this stage they do not lie contentedly curled and pearly at the bottom of the cell, instead they have a grey or yellow tinged appearance and move about as if they were “suffering from stomach ache” (Hooper). They die in attitudes of distress, twisted or spiralled in the cell, and look like wax larvae that have been held too close to a flame; this is what is known as the ‘melted down’ appearance. The tracheal system and the gut may be whitely visible at this stage which is due to the tightly packed bacterial contents.
  • There may also be some smell or there may be a strong one (Hooper). In advanced cases it could be reminiscent of rotting fish (Gochnauer). Whatever it smells like, it is due to secondary infections by putrefying bacteria and probably fungi too.
  • Some larvae may succumb after capping so there could be some sunken and/or perforated cappings as in AFB
  • There may be an erratic or patchy brood pattern as the queen lays in newly cleaned cells of killed larvae.
  • There may be some ropiness of cell contents but if so there will be a strong and offensive smell and there will be a granularity to the ropiness. If the remains do dry down to a scale this tends to be rubbery (Morton) and can be easily removed unlike the recalcitrant A.F.B. scale.
  • Due to the ephemeral nature of the visible signs of the disease the beekeeper must be vigilant and be sure to include checks for EFB in his regular routine hive inspections.
Confirmation of disease

The above should be field-confirmation for the beekeeper but to be sure he should then take a sample of comb with suspect larvae and send it, wrapped not too tightly, in newspaper to Teagasc who will do a microscopic examination and confirm, or not, as the case may be.

Routine sampling twice a year would not be a bad idea in order to be sure.

Treatment

Opinion regarding treatment is divided. All but the most seriously affected colonies (<50%) can be treated by dosing with the antibiotic oxytetracycline (OTC) (Hooper, Morton, FERA). A single one gram dose suspended in a small volume of sugar solution is sprinkled over and around the brood nest then 5-10 litres of a strong sugar syrup is fed to the bees to ensure the dose is distributed widely and slowly around the brood box.

Seriously affected colonies (>50%) must be destroyed and burned as for AFB.  O’Sullivan recommends destruction and burning as the only treatment – as per AFB.

But there is an alternative to this – the shook swarm is a highly effective treatment for EFB and is even recommended by FERA.

Prevention of spread

The mode of infection is less clearly understood than AFB but the beekeeper is still the main cause of the spread. Colony and apiary quarantine need to be applied. Quarantine time should be at least 8 weeks after treatment.

Colonies that have been treated should be housed on new foundation to help prevent reinfection.

Apart from that, according to Hooper infection is thought to be more through drifting than robbing, although he is sceptical. If, despite Hooper’s doubts, drifting is the cause of spread then it can be reduced, if not prevented, by siting hives at angles to each other rather than in rows and not allowing grass and weeds to grown too high.

The beekeeper should alert his/her neighbouring beekeepers so that they can be on the lookout and treat if necessary.

Colony quarantine

When a beekeeper thinks he has found EFB (or other disease) in a colony, but before confirmation and treatment, then to try and prevent spread, efforts should be made to isolate the affected colony as much as possible.

After samples of bees and comb have been taken for microscopic analysis by Teagasc then gloves, boots, beesuits, hive tool, and even the bellows of the smoker must all be thoroughly scrubbed with strong washing soda solution (Browne) or soapy water (Morton).

After complete disinfection of all equipment, the other hives in the colony must be gone through very carefully to check for disease. Whether or not signs of EFB are visible, samples should be taken from all other colonies and sent for analysis. Care should be taken to ensure that the samples are correctly marked with hive number etc. Equipment should be disinfected between colony inspections.

All hive parts should be marked with the hive number to make sure that they aren’t mixed up which could spread disease.

Apiary quarantine

On no account move bees or equipment from infected apiary to uninfected apiaries. Wash all clothing but preferably leave it where it is. When Teagasc reports back with results of analysis all affected hives must be dealt with as above. Quarantine must be maintained for at least 6 weeks after treatment but can be relaxed after this time if no further sign of the disease is found.

There is evidence that the Shook Swarm can be used to treat EFB.

Click here for more about the Shook Swarm Method

Sources

Browne,L. Apiary Hygeine and Diseases. Gormanston 2000.

Burke,J., Dunne,R., Bennett,P., & MacGiollaRi,P. Profitable Honey Production. Teagasc. Dublin. 1996.

FERA. Foulbrood Disease of Honey Bees
and other common brood disorders The Food and Environment Research Agency 2013

Gochnauer,T.A., Furgala,B. & Shimanuki,H. Diseases and enemies of the honey bee. In The Hive and the Honey Bee. Ed. Dadant and Sons. Dadant Publications. Illinois. USA. 1979.

Hooper,T. Guide to Bees and Honey. Blandford, London. 1991.

M.A.F.F. Statutory Procedures for Controlling Foul Brood. Central Science Laboratory National Bee Unit. M.A.F.F. U.K.

Morton,J. & Brown,M. Foul Brood Disease: Recognition and Control. Central Science Laboratory National Bee Unit. M.A.F.F. U.K.

O’Sullivan,E. Beekeeping Problems. In Bees, Hives and Honey – The Beekeeper’s Companion. Ed. Eddie O’Sulllivan. FIBKA. Ireland. 2000.

Snodgrass,R.E. The Anatomy of the Honey Bee. In The Hive and the Honey Bee. Ed. Dadant and Sons. Dadant Publications. Illinois. USA. 1979.

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