B452 - AMERICAN FOULBROOD

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B452 - AMERICAN FOULBROOD

Nature of the disease
American foulbrood (AFB) is a serious bacterial disease that attacks the brood of honey bees. The disease is caused by a spore forming bacteria — Paenib.
Classification
OIE List B disease.
Susceptible species
The honey bee Apis mellifera and other Apis spp. are susceptible.
Distribution
AFB is widely distributed, in western and eastern Europe, the former Soviet Union, North and Central America and part of South America, Africa and Asia.
It has also been reported from a number of Pacific Island countries and Territories, including New Zealand.
Clinical signs 
  • Combs of infected colonies have a mottled appearance
  • Cell cappings containing diseased larvae appear moist and darkened
  • Larval and pupal colour changes to creamy brown, then dark brown
  • Unpleasant odour in advanced stages
  • Larvae and pupae infected with AFB display a characteristic "ropiness" when a small stick is used to slightly stir the diseased tissue in the cell and then stick is slowly removed
  • Death in the pupal stage results in the formation of the pupal tongue, a protrusion from the pupal head which is one of the most characteristic signs of the disease
  • Diseased brood eventually dries out to form characteristic brittle scales adhering tightly to the cells
Post-mortem findings
Infected larvae died in erect position, and the tongue may persist in the dried scale.
Differential diagnosis
 
Specimens required for diagnosis 
AFB can usually be diagnosed in the field. A simple test is the Ropiness test. It consists in the insertion of a small stick into the suspect larva or pupa the stick is used to mix up the brood remains and when it is removed the tissues will draw out in a fine thread between 10 and 30 mm long.

Laboratory tests are available for confirming diagnosis by microscopy, or preferably by fluorescent antibody technique but risk of confusion with P. alvei exists.
The absolute identification of P. larvae is made by culture from comb or honey samples.

A sample of comb, at least 9 cm² and containing as much of the dead or discoloured brood as possible and little or no honey. The sample should be loosely wrapped in paper and dispatched in a heavy cardboard or wooden box. Plastic, aluminium foil and glass are likely to cause mould sample.

Transmission
Only the bacterial spores are capable of inducing the disease. Infection of bee colonies is primarily caused by plundering of ill and weakened or already extinct bee colonies. Infection is transferred by bee-feeders, through foodstuffs, into larvae. There the spores change into vegetative form and reproduce, causing larval decomposition with subsequent sporulation. When cleaning infected cells, bees distribute spores throughout the entire colony.

Infection can also be spread by feeding fees infected honey or pollen, by using affected honeycombs or infected hives, or by using contaminated beekeeping tools.

Spores are very resistant, they can survive very high temperatures and remain viable for up to 60 years!

Risk of introduction
AFB may be introduced with live bees and brood, contaminated honey or beekeeping equipment.
Control / vaccines
Prevention of AFB is accomplished by good management procedures.

This may include eliminating colonies that are suspected of having the disease and/or feeding an antibiotic such as oxytetracycline.

In countries where AFB occurs, a great deal of controversy exists concerning feeding antibiotics to honey bee colonies for prevention of AFB. Most large-scale beekeepers find it more efficient to routinely treat their bees. On the other hand, many small-scale operators do not follow such a feeding program, preferring instead to let symptoms appear and then have the bee inspector diagnose and then burn the colonies. This removes disease reservoirs and eliminates susceptible stock, not possible where preventative feeding with antibiotics effectively may mask all symptoms.

References
  • Office International des Epizooties, 2002
  • SPC, Paravet Programme, 2001