Description

AES: American Foulbrood (AFB), European Foulbrood (EFB), Sacbrood Virus (SBV)

American foulbrood (AFB) is a highly infectious brood disease caused by the spore-forming bacterium, Paenibacillus larvae. It is the most widespread and destructive of the bee brood diseases (Frazier et al., 2015). Larvae become infected by ingesting spores found in the food. AFB spores are extremely resistant to desiccation and can remain viable for more than 40 years in honey and beekeeping equipment. Therefore, honey from an unknown source should never be used as bee feed and used beekeeping equipment should be assumed contaminated unless known to be otherwise. Because of the persistence of the spores, many State Apiary Inspectors require an AFB diseased hive to be burned completely or at the very least burning the frames and comb and thoroughly flame scorching the interior of the hive body, bottom board and covers as a means of containing the spread of disease (www.beeinformed.org).

EFB is a bacterial brood disease caused by Melissococcus plutonius (Frazier et al., 2015). It is considered a stress disease and is most prevalent in spring and early summer. EFB usually does not kill colonies and is less serious than AFB. EFB does not form spores, but often overwinters on combs. It enters the larva in contaminated brood food and multiplies rapidly within the gut of the larva. EFB frequently disappears with a nectar flow (Frazier et al., 2015).Occasionally, the disease remains active throughout the entire foraging season. All castes of bees are susceptible, although strains differ in susceptibility (Frazier et al., 2015). The most significant symptom of EFB is the non-uniform color change of the larvae. They change from a normal pearly white to yellowish, then to brown, and finally to grayish black; they can also be blotchy or mottled. Larval remains often appear twisted or melted to the bottom side of the cell. The dead larvae form a thin, brown or blackish brown scale that can be easily removed (Frazier et al., 2015).

SBV is a disease caused by a virus that usually does not result in severe losses (Frazier et al., 2015). It is most common during the first half of the brood-rearing season and often goes unnoticed, since it affects usually only a small percentage of the brood (Frazier et al., 2015). Adult bees typically detect and remove infected larvae quickly. If Sacbrood is widespread enough for the beekeeper to observe the symptoms, the disease may be so severe that the adult worker population becomes reduced. SBV is transmitted through nectar and pollen that contains the virus. Diluted nectar is less likely to cause infection than when the virus is concentrated in a pollen pellet. Therefore, use caution when transferring frames with pollen among colonies. Little is known of the other transmission routes. Sacbrood usually subsides in late spring when the honey flow begins, but if symptoms persist, re-queening with hygienic stock is recommended (Frazier et al., 2015).

References

Bee Informed [Online]. Pest and Disease Control – American Foulbrood. Available: https://beeinformed.org/.

Frazier, M., Caron, D. M., VanEngelsdorp, D., Pennsylvania State University. College of Agricultural, S., Mid-Atlantic Apiculture, R., Extension, C. & United States. Department of, A. 2015. A field guide to honey bees and their maladies, Pennsylvania State University.