American Foulbrood

Paenibacillus larvae

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Changed on: 23.01.2019
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American foulbrood is a contagious disease of the bee brood diseases that requires substantial combating and rebuilding work should there be an outbreak. The pathogen can only affect bee larvae and is harmless to humans. Honey contaminated with spores can be eaten without risk.

The pathogen, Paenibacillus larvae, is a gramnegative, rod-shaped bacteria, which appears in two forms: as a fully flagellated rod (reproductive form) and as a spore (resistant dormant form).

More information

American foulbrood is a contagious disease of the bee brood diseases that requires substantial combating and rebuilding work should there be an outbreak. The pathogen can only affect bee larvae and is harmless to humans. Honey contaminated with spores can be eaten without risk.

The pathogen, Paenibacillus larvae, is a gramnegative, rod-shaped bacteria, which appears in two forms: as a fully flagellated rod (reproductive form) and as a spore (resistant dormant form).

More information

Symptoms

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festsitzende Schorfe /
sticky scabs
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Weiselzelle mit Faulbrutschorf /
queen cell with foulbrood scab
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fadenziehender Inhalt der Wabe /
thread-like, slimy cell content

There could be several weeks or months between the actual infection and outbreak (= first visible symptoms), depending on the condition of the colony and the bacteria strain; there are five different documented genotypes in Austria).

American foulbrood (AFB) is a highly contagious, bacterial infection of the bee brood, which leads to the death of the brood, Typical clinical symptoms are: patchy hive; sunken, holey, moist, shimmering cell caps; left over, closed brood cells; light to dark brown, thread-like, slimy substance in the cell; sticky scabs in the lower channel of the cell; and the possible characteristic of a glue-like odour to the slimy substance.

Progression of Disease

The larvae are infected by ingesting the spores together with their food. Larvae that are one to two days old can be infected. The spores develop into rod-shaped bacteria in the larvae’s mi-gut area after 24 hours. There, the bacteria reproduce on a massive scale for one to four days after the infection. They subsequently manage to break through the intestinal epithelium in some places, moving between the intestinal epithelial cells into the larvae’s body cavity in large numbers. Should this happen, the larvae will die. The rod-shaped bacteria then turn into spores. Spores may already be produced in limited numbers at the beginning of the infection.

Depending on the foulbrood strain, the larvae that already die at an early stage (prior to cell capping) are removed by worker bees responsible for cleaning the hive to differing levels. Thus, the disease’s symptoms could become apparent through more or less extensive breeding holes, depending on how much of the infected brood has been removed before cell capping. Should this be the case, it can be difficult to diagnose American foulbrood in the colony (thus, always look out for a brood nest with holes!). The typical symptoms for American foulbrood only become visible when the larvae die after the cell closes:  the slimy substance, which can dry later and form scabs.

Transmission

Transmission within the Colony

Foulbrood spores can be transmitted within an infected colony in the course of normal colony activities, as all parts of the bee colony and the hive can be contaminated with spores. Spores can be found in scabs on combs, the honey, pollen, on bees (coats), inside bees (honey stomach, mid-gut, rectum), on hive body surfaces, in propolis and bee excrements, as well as bee moth excrement.

Transmission between Colonies

Transmission occurs via the bees themselves (robbing: robbing honey from weaker colonies; also “silent” robbing, swarms, returning to the wrong hive and drones) and also via the beekeeper (comb exchanges between contaminated and healthy colonies; the formation of new colonies from infected ones; the removal or addition of brood, honey and pollen combs to strengthen or split a colony; as well as feed supplies, the use of contaminated equipment for different colonies and hives, the concentrating of colonies in one location or area, the “licking clean” honey-wet combs and the capping of wax inside the hive or outdoors, in addition to the feeding of honey or pollen from third parties or from aboard.

Prevention

Do not bring foreign colonies, combs and equipment to a hive that has not been tested first.

Only buy colonies after having examined the brood (at the original hive).

Disinfect second-hand hives and equipment before using them.

Do not feed foreign honey, pollen or honey from abroad to your colony.

Do not set up beehives near danger sources (neglected hives, plants processing honey from abroad, landfills).

Starve foreign swarms in the swarm box until the first bees start to drop, so the feed reserves in the honey stomach are used up.

Combating American Foulbrood

American foulbrood is combated either by destroying or rebuilding colonies, together with additional disinfection measures. There is no drug that has been approved in Austria to combat American foulbrood. The authorities and experts have issued strong warnings against the use of antibiotics, as this could result in substantial risks (e.g. residues in the honey, unnoticed spreading of the disease) and fines by the regulatory authorities. Honey contaminated with antibiotic residues is not marketable, neither as a food or as animal feed.

For detailed information on rebuilding and disinfection, see download: American Foulbrood – Information for Beekeepers (in German).

The most common method to rebuild a bee population after an outbreak of American foulbrood is the shakedown method, in combination with extensive disinfection measures. Each hive with contaminated colonies must go through the complete shakedown process. This process should be carried out as early as possible, following the diagnosis of the disease. The possible timeframe for colony and hive restoration -- adjusted to the given climate and weather conditions: March to September (time of the first population expansion to the end of the feeding period).

Ideally, all hives containing infected colonies should be rebuilt in a containment area within a short amount of time.

The shakedown method can be applied to all colonies, in principle. In the case of weaker colonies, shook swarms can be created using the stronger queen.

It is advised to cull infected colonies, if they are already very weak or forming an artificial swarm is no longer possible due to the time of the year (hibernation period between October and March).

All brood combs and frames need to be burned, other combs (even the storage combs) must be cut out, labelled “Seuchenwachs” (contaminated wax) and melted at a wax processing company.
Should there be an epidemic, do not process the wax yourself.

Should AFB be diagnosed at a major pollen-gathering area, the local authorities must be asked to approve a step-by-step procedure:
The clinically infected colonies of a hive should be culled or rebuilt immediately. Set up the shook swarms at this hive.
Shake off all colonies after they have brought in the nectar and pollen (maybe caging the queen for three weeks, so the colonies are brood-free after collecting the nectar and pollen).


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