American foulbrood is a contagious disease of bee brood caused by the bacterium Paenibacillus (P.) larvae, which requires extensive control and sanitation measures in case of occurrence. Paenibacillus larvae is a gram-positive, rod-shaped bacterium that occurs in two forms: as a round flagellated rod (multiplication form) and as a spore (very resistant permanent form, can remain infectious for more than 40 years).

Worldwide

The spores are found in materials from diseased colonies (combs, honey, frames, etc.). Since the pathogen can only infect bee maggots, it is harmless to humans. Honey contaminated with spores can therefore be consumed without risk.

Ingestion of the spores with the food leads to infection of the larvae. Maggots aged one to two days can be infected. In the midgut, the spores develop into rod-shaped bacteria after only 24 hours. These multiply there en masse one to four days after infection. Subsequently, they succeed in overcoming the intestinal epithelium in some places by migrating between the intestinal epithelial cells and then suddenly enter the abdominal cavity in large numbers. When this occurs, the larva dies. The rod-shaped bacteria reform into spores. Spores may be formed on a smaller scale from the onset of infection.

Transmission in the colony

In the course of normal colony activity, foulbrood spores can be transmitted in the infected colony because all parts of the colony and hive are contaminated with spores. Spores are found in scabs on combs, in honey, in pollen, on bees (hair coat), in bees (honey bladder, midgut, fecal bladder), on hive surfaces, in putty resin, in bee feces, and in wax moth feces.

Transmission from colony to colony

Transmission occurs both through the bees themselves (predation: honey theft from weak colonies; also "silent" predation, swarms, flight of bees and drones) and through the beekeeper (honeycomb exchange between diseased and healthy colonies, formation of offspring from diseased colonies, honeycomb exchange during the addition or removal of brood, honey, and other materials). (exchange of combs between diseased and healthy colonies, comb exchange from diseased colonies, comb exchange when adding or removing brood, honey and pollen combs for strengthening or cupping the colonies and for feeding, use of contaminated equipment for different colonies and stands, massing of colonies at one location or in one area, "licking out" of honey-moist combs and uncapping wax in the hive or in the open, feeding of honey and pollen from outside or from foreign sources.

Between infection and disease outbreak (= first signs of disease visible) often weeks to months pass, depending on the condition of the bee colony, infection pressure and bacterial genotype. In Austria, the genotypes ERIC I and ERIC II have been detected.

American foulbrood (AFB) is a highly contagious bacterial infection of bee brood that leads to brood death and typical clinical symptoms:

• patchy brood nest
• sunken, holey, moist and shiny cell covers
• remaining capped brood cells
• light to dark brown, stringy mass in the brood cell
• stuck scabs in the lower groove of the brood cell
• possibly characteristic smell of the slimy mass like glue

American foulbrood is controlled either by destruction or by sanitation of the colonies with accompanying disinfection measures. In Austria, no drug is approved for the control of American foulbrood.

• Do not bring foreign colonies, combs and equipment to the stand without inspection.
• Buy colonies only after a forage inspection with negative results and brood control (at the stand of origin).
• Disinfect used hives and equipment before use.
• Do not feed foreign honey, pollen or honey from abroad
• Do not place apiaries near sources of danger (abandoned apiaries, foreign honey processing plants, garbage dumps).
• Let foreign swarms starve in the swarm box until the first bees fall down, so that the food supply in the honey bladder is used up.

American foulbrood is widespread in Austria. The number of reported outbreaks varies greatly from year to year.

There are different strains or genotypes of P. larvae that differ in terms of virulence, which also influences symptomatology and detection by beekeepers or bee experts. In research projects, two of the five known ERIC genotypes have been detected in Austria so far. They are not routinely distinguished in the course of testing official samples. In the presence of the ERIC I genotype, a significant proportion of the diseased larvae reach capping and only die afterwards, resulting in the mass formation of spores. Typical signs are capped cells with filamentous masses and stagnant cells. The course of the disease in the colony is rapid.

In the presence of the ERIC II genotype, diseased larvae usually die before capping and the cells with dead brood are cleaned out by the bees. This leads to a patchy brood nest. Since this is a non-specific symptom that can also be caused by other brood diseases or damage, there is a risk that the disease will not be detected for a long time.

A disease outbreak should be controlled as quickly as possible, since pathogen spread occurs through flight of bees or even predation. Therefore, unattended, neglected apiaries can be a potential source for the spread of American foulbrood. Such stands or honeycomb material stored freely accessible to bees are often only discovered during the inspection of the 3-km exclusion zone.

Therapy

For the sanitation of an outbreak of American foulbrood, the sweep swarm method in combination with extensive disinfection measures is the method of choice. Every stand with diseased colonies must be completely subjected to the swarm sweeping procedure. Sanitation should be carried out as soon as possible after the disease is diagnosed. Possible period of sanitation, which is to be adjusted to the respective climatic or weather conditions: March to September (time of the first expansion until the end of feeding). Ideally, all stands with diseased colonies within a restricted area (restricted area with a 3-km radius) should be sanitized within a short period of time.

• Sweep off the colony
• Plan starvation phase with or without cellar detention
• Place artificial swarm on middle walls
• Sufficient liquid feeding (also stimulates the cleaning instinct)
• Melting of the combs
• Scrape wax and propolis residues from the inside of the hive or clean them with a steam jet.
• Washing of equipment (chisels, feeders) and hives with 3 % hot soda lye; rinse with clean water (ATTENTION - soda lye is corrosive; protective clothing (goggles, gloves) is therefore absolutely necessary)
• Flaming of the hives with gas burner
• Clean honeycomb cabinet and beehive and possibly flame them; clean non-flammable parts with lye.

The sweep swarming method is basically feasible for all colonies. If the strength of the individual colonies is too low, collective sweep swarms can also be formed using the better queen. It makes sense to kill sick colonies if they are already very weak or if the time of year (overwintering period between October and March) does not allow the formation of sweep swarms. All brood combs are to be burned, all other combs (including all storage combs) are to be cut out and melted down at a wax processing plant - declared as "epidemic wax". No own wax processing in case of epidemic. If American foulbrood is diagnosed during a mass harvest, the consent of the district administrative authority should be obtained for a step-by-step procedure: Immediately kill or sanitize the clinically diseased colonies in a stand. Place these sweep swarms in the stand. After the end of the harvest, sweep all colonies of the stand (queen may be caged for three weeks so that the colonies are brood-free after the harvest).

Any suspicion of American foulbrood must be reported to the competent district administrative authority (district administration, magistrate). This authority will instruct the official veterinarian (ATA) or an expert to inspect the colonies for clinical symptoms. If disease symptoms are present, a brood sample will be sent to the official testing laboratory (National Reference Laboratory for Bee Diseases, AGES).

For American foulbrood, a two-step diagnostic procedure is used: the inspection of brood combs for clinical symptoms and the microbiological culture procedure. Other diagnostic procedures (PCR, ERIC typing) are only carried out on a random basis as part of research activities.

Sample submission

Brood comb piece with diseased brood