European foulbrood (EFB) is
a serious, notifiable bacterial disease of honeybee brood
of international proportion. Its incidence is apparently
increasing and there is considerable pressure from beekeepers
to improve EFB control. European foulbrood is sometimes
not regarded as such an important disease as American
foulbrood yet the two are often confused or mis-diagnosed.
In the UK around 50% of EFB-infected colonies per year
are destroyed, with costs to beekeepers also posed by
standstill notices on infected apiaries (in place for
years in some areas), losses of honey yields, pollination
contracts and sale of bees.
Several bacterial organisms are associated with an infection
of European foulbrood but the main causative organism
within the complex is Melissococcus plutonius. Apparition
of disease seems to be linked to stress conditions, lack
of food, water, space or additional disease or pest attack;
however queen genetics, weather and geography may also
play a part. EFB infection tends to be localised and
will recur in but is not restricted to the same apiaries
year after year.
Very young larvae are particularly susceptible and become
infected through being fed brood food contaminated with
M. plutonius. The bacteria multiply rapidly in the larval
mid-gut reaching such enormous numbers that the bacteria
competes with the bee for food supply. Larval death is
primarily through starvation, usually around the time
of cell capping.
Disease symptoms are more obvious in the honeybee colony
in early spring and summer yet the pathogen may remain
relatively dormant within the hive for extended periods.
As infection with EFB typically involves a complex of
organisms, the symptoms of the disease vary and accurate
diagnosis is not always straightforward. Vita has with
Pocket Diagnostics developed the Vita Diagnostic Test
Kit for the early detection of EFB. This enables every
beekeeper to test their hives at the first suspicion
of the presence of EFB.
In severe infections the colony exudes a foul, rotten odour (hence foulbrood)
but this is only one possible symptom of the disease. As in American foulbrood
(AFB) infections, the brood pattern in EFB-affected colonies can be patchy.
Bee larvae infected with European foulbrood appear twisted
in their cells, their bodies sometimes forming an unnatural
C-shape along the sides or in the bottoms of the cells.
The tracheal system may stand out, silvery in appearance.
The gut is sometimes visible through the opaque body
tissue. The infected larvae turn yellow and then brown
eventually drying to rubbery scales within the cells.
In differentiation to AFB, the cadaver cannot be “roped
out” with a matchstick or similar implement; it
is not glue-like as in AFB and these drier EFB scales
can be more easily removed by the worker bees.
Good husbandry in beekeeping
practice will help reduce other stresses on the honeybee
colony and possibly prevent or limit the expression of
European foulbrood.
There is some suggestion that M.plutonius is much more
widespread and resident in colonies than expected yet
the disease is triggered only when supplementary stresses
affect the colony.
Even though M. plutonius is not a spore-forming bacillus,
some bacteria may survive on combs to re-infect the following
or subsequent season. A “shook swarm” method
is recommended by the National Bee Unit of the UK, where
adult bees are shaken from previously infected and treated
comb to new hives with fresh foundation. The recurrence
of EFB following this method is very much reduced.
In other countries, administration of oxytetracycline
is permitted as a preventative as well as a curative
treatment.
Difficulties associated with this type of regime include
cost to the beekeeper, residues of antibiotics in hive
products and more recently the emergence of oxytetracycline-resistant
bacteria.
Vita (Europe) Limited in conjunction with the National
Bee Unit and Cardiff University have won UK government
funding for a research project evaluating a new biological
control agent for European foulbrood. A harmless bacterium
found as a commensal in beehives has been shown to control
Melissococcus plutonius infections under laboratory conditions.
Studies on the toxicity and palatability of the bacterium
show no effect on the bees.
Field tests are underway and current progress is positive.
A new, natural product may be available from Vita (Europe)
Limited for the treatment of European foulbrood within
the next few years.
