What is European foulbrood?
European foulbrood (EFB) is a brood disease of honey bees caused by the bacterium Melissococcus plutonius. The disease is found in most parts of the world where honey bees are kept, however it has so far, not been found in New Zealand.
The visual symptoms of EFB can be misdiagnosed as AFB. For instance, in advanced stages with EFB, larvae may die after the cell has been capped. The brood pattern may appear patchy and some cappings may be sunken or perforated as is the case of AFB. Larvae affected by both diseases also eventually dry down to form scale.
Differences to AFB
There are a number of distinctive differences in the symptoms of these two brood diseases, for example the stage of development at which the larva succumbs. In the case of EFB, death always occurs before the larva lies out fully along the bottom wall of the cell (prepupal stage). Death usually occurs when the larva is still curled in a c-shape in the cell. There are circumstances, however, when the larva dies in the transition between this c-shape and full extension. In such cases, the larva appears to be twisted, in a cork-screw shape, from the bottom through to the top of the cell.
AFB infected larvae and pupae are never found in either the c-shape in the bottom of the cell, or twisted in a cork-screw shape. AFB infected brood are always found in the prepupal or pupal stage. EFB infected brood are never found in the pupal stage, and the remains of tongues are never present.
Another distinctive difference is the colour of brood affected by the two diseases. In EFB, infected larvae turn from the normal pearly-white colour to yellow. Outlines of the larva’s tracheae also appear as light lines amongst the yellow tissue. Tracheal outlines are never prominent in the larva affected by AFB.
EFB infected larvae occasionally rope out when a stick is inserted into the cell and slowly withdrawn. The roping is caused by the presence of other bacteria in addition to EFB that are feeding on the dead larva.
When the remains of EFB infected larvae dry out, a distinctive c-shape scale is formed. Unlike AFB scale, this scale can be easily removed from the cells.
The smell of EFB infected larvae is sour and urine-like, and is not similar to the fishy smell associated with AFB. However, because of the variability in people’s ability to detect and differentiate odours, smell should never be used to diagnosis either disease.
Although EFB is currently not found in New Zealand, beekeepers should still be aware of the symptoms of the disease, and should always immediately contact the Ministry of Agriculture and Forestry who may arrange for a sample to be sent to a laboratory. Beekeeper vigilance is the first line of defence in keeping New Zealand free of unwanted honey bee pests and diseases.
If a suspect case of EFB is found, contact the New Zealand Ministry of Agriculture and Forestry immediately on 0800 809 966.