American foulbrood (AFB, ''Histolysis infectiosa perniciosa larvae apium'', ''Pestis americana larvae apium''), caused by the spore-forming bacterium ''

Paenibacillus larvae ''Paenibacillus larvae'' is a species of bacterium, found worldwide, which causes American foulbrood, a fatal disease of the larvae of honeybees ('' Apis mellifera''). It is a Gram-positive In bacteriology, gram-positive bacteria are bacteria ...

'' (reclassified as one species without subspecies differentiation in 2006 from ''Paenibacillus larvae'' ssp. ''larvae,'' formerly classified as ''Bacillus larvae'', and ''Paenibacillus larvae'' ssp. ''pulvifaciens''), is a highly infectious

honey bee A honey bee (also spelled honeybee) is a eusocial flying insect within the genus ''Apis'' of the bee clade, all native to Afro-Eurasia. After bees spread naturally throughout Africa and Eurasia, humans became responsible for the current co ...

brood disease. It is the most widespread and destructive of the honey bee brood diseases. It is globally distributed and burning of infected colonies is often considered as the only effective measure to prevent spreading of the disease.

Characteristics

'' is a rod-shaped bacterium, which is visible only under a high power microscope. Larvae up to 3 days old become infected by ingesting

spores In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...

that are present in their food. Young larvae less than 24 hours old are most susceptible to infection. Spores germinate in the gut of the larva and the vegetative form of the bacteria begins to grow and multiply until the midgut is massively filled with bacteria and it comes to a shortage of nutrients (

commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fro ...

non-invasive phase). This is when ''P. larvae'' breaks through the midgut wall and enters the hemocoel of the larva which is accompanied with the death of the larvae (invasive phase). Now, the bacteria take the nourishment from the dead larva and decompose it to a ropy mass (

saprophytic Saprotrophic nutrition or lysotrophic nutrition is a process of chemoheterotrophic extracellular digestion involved in the processing of decayed (dead or waste) organic matter. It occurs in saprotrophs, and is most often associated with fungi ( ...

phase). When it comes to another shortage of nutrients while the larva is decomposed, ''P. larvae'' produces millions of spores. The ropy mass dries down to a characteristic scale. This disease does not affect the adult honey bees but is highly infectious and deadly to bee brood.

History

Until 1906 American foulbrood was not differentiated from European foulbrood, and the condition was simply referred to as foulbrood. Thereafter, the terms European and American were used to distinguish the diseases. However the designations do not refer to the geographical distributions but to the areas where they were first investigated scientifically. In 1907, it was demonstrated conclusively that the bacterium ''Bacillus larvae'' was the cause of American foulbrood disease by fulfilling

Koch's postulates Koch's postulates ( )"Koch"
''

Disease spread

When cleaning contaminated cells, bees distribute spores throughout the colony. Disease spreads rapidly throughout the hive as the bees, trying to remove the spore-laden dead larvae, contaminate brood food. Nectar stored in contaminated cells will contain spores and soon the brood chamber becomes filled with contaminated honey. As this honey is moved up into the supers, the entire hive becomes contaminated with spores. When the colony becomes weak from AFB infection, robber bees may enter and take contaminated honey back to their hives, thereby spreading the disease to other colonies and apiaries. Beekeepers also may spread disease by moving equipment (frames or supers) from contaminated hives to healthy ones. American foulbrood 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 to be contaminated unless known to be otherwise. Foul Brood Beehives

Treatment

European Union The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been des ...

law requires all infected hives and equipment to be destroyed. In the US, many State Apiary Inspectors require an AFB diseased hive to be burned completely. The spores can survive up to 40 years and are difficult to destroy. A less radical method of containing the spread of disease is burning only the frames and comb and thoroughly flame scorching the interior of the hive body, bottom board and covers. Dipping the hive parts in hot

paraffin wax Paraffin wax (or petroleum wax) is a soft colorless solid derived from petroleum, coal, or oil shale that consists of a mixture of hydrocarbon molecules containing between 20 and 40 carbon atoms. It is solid at room temperature and begins to ...

or a 3%

sodium hypochlorite Sodium hypochlorite (commonly known in a dilute solution as bleach) is an Inorganic chemistry, inorganic chemical compound with the chemical formula, formula NaOCl (or NaClO), comprising a sodium cation () and a hypochlorite anion (or ). It may ...

solution (bleach) also renders the AFB spores innocuous. It is also possible to sterilize an infected hive without damaging either the structure of the hive or the stores of honey and pollen it contains by sufficiently lengthy exposure to an atmosphere of

ethylene oxide Ethylene oxide is an organic compound with the chemical formula, formula . It is a cyclic ether and the simplest epoxide: a three-membered Ring (chemistry), ring consisting of one oxygen atom and two carbon atoms. Ethylene oxide is a colorless a ...

gas, as in a closed chamber, as hospitals do to sterilize equipment that cannot withstand steam sterilization. Antibiotics, in non-resistant strains of the pathogen, can prevent the vegetative state of the bacterium forming. Drug treatment to prevent the American foulbrood spores from successfully germinating and proliferating is possible using oxytetracycline hydrochloride (Terramycin). Another drug treatment, tylosin tartrate, was approved by the US

Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respon ...

(FDA
in 2005
Chemical treatment is sometimes used prophylactically, but this is a source of considerable controversy because certain strains of the bacterium seem to be rapidly developing resistance. In addition, hives that are contaminated with millions of American foulbrood spores have to be prophylactically treated indefinitely. Once the treatment is suspended, the American foulbrood spores germinate successfully again leading to a disease outbreak. Alternative treatments are currently under investigation. One example is

phage therapy Phage therapy, viral phage therapy, or phagotherapy is the therapeutic use of bacteriophages for the treatment of pathogenic bacterial infections. This therapeutic approach emerged at the beginning of the 20th century but was progressively re ...

. Another promising approach might be the use of lactic acid-producing bacteria as a treatment for AFB. However, further research is still indispensable to proof the effectiveness of these methods in the field.

References

External links

Learn to identify American foulbrood in 90 seconds
YouTube video showing the 'Ropiness test' and scales. {{BeeColonyMemberTypes, state=collapsed Western honey bee pests Bee diseases