American Foulbrood (AFB) is a widely distributed disease of honey bee brood (larvae and pupae) caused by the spore-forming bacterium Paenibacillus larvae that leads to colony death and economic losses. Spores of the bacterium are heat and cold tolerant and antibiotic resistant, and may persist on contaminated beekeeping equipment for over 50 years. While not common in Hawaii, the disease was accidentally introduced and decimated the state’s beekeeping industry in the 1930s. It was common through the 1950s, though there is a lack of consistent record keeping. Since 2012, there have been at least 10 confirmed cases, mostly on the Big Island.

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Spores are fed to 12-36 hour old larvae by adult nurse bees, which infect their gut. They eventually invade other areas of their body and kill the insect. Spores are moved between colonies by robbing or drifting adult bees. Beekeepers may facilitate the spread of spores by using contaminated equipment in healthy colonies, recycling used equipment, or combining weak colonies. Rapid spread of AFB between colonies is most common in areas with high colony densities. 

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The primary clinical symptom are brownish, semi-fluid larvae that form a “ropey mass.” Other symptoms include irregular brood capping (“shotgun” brood pattern); dark, sunken, greasy, irregularly punctured caps; a foul odor like rotting fish**, and; a hard scale formed by dead larvae at the bottom of the cells. Larvae may appear caramel colored, and pupae may have tongues sticking out.

**The absence of odor does not mean an absence of AFB, and an odor does not necessarily mean the presence of AFB as larval decay for any reason will smell unpleasant. Look for a combination of relevant symptoms present within the colony.

Shotgun brood pattern, indicative of a diseased colony. Photo by R. Snyder, beeinformed.org.

Sunken and punctured cell caps (yellow), dead larval scales (blue) and discolored larvae (pink), together indicative of AFB infection. Photo by R. Snyder, beeinformed.org.

AFB positive rope test (left) and pupal tongue (right). Photos by I. Ashe, West Hawaii Today.

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AFB infection may be confirmed in one of three ways:

1. By performing a rope test - cells with dead larvae are punctured and the mixed contents drawn out. If they can be pulled to one inch before breaking, this is strongly diagnostic of AFB.

2. Holst milk test - This is an effective and inexpensive make-at-home test specific for AFB. Click here for a comprehensive description for how to make your own kits (pages 15-16). 

3. Vita® AFB test kit - this functions similarly to a pregnancy test. Kits can be purchased from beekeeping supply companies. Suspected diseased larvae are ground in the provided vial and a drop of solution placed on the applicator. A blue line will appear at "C" to indicate the test is working. Any line, however faint, at "T" is positive for AFB.

If any of these tests are positive, this should be reported to the Hawaii Apiary Inspectors (808-973-9538).

Additionally, you are encouraged to submit a sample to the USDA-ARS honey bee disease diagnostic service in Beltsville, MD, which also offers antibiotic resistance testing. Instructions for sending samples may be found here.

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· Antibiotics—Oxytetracycline, tylosin, and lincomycin are registered for use against AFB infections but are only available by prescription from a veterinarian (see below for a contact list by county). However, antibiotics may mask symptoms by not killing spores which are the drivers of infection, so long-term use is not sustainable. Overuse may lead to resistance. Residues may appear in bee products such as honey. Remove honey supers before treating. Use judiciously in mild to moderately infected colonies.

· Burning—This is the recommended strategy for infected colonies to prevent the spread to healthy neighboring colonies. After dark, seal the colony and place the entire colony (hive bodies, frames, adults and queen) in a hole, burn to ash, and bury. Acquire a burn permit before doing so. The remaining colonies in the apiary should be treated with antibiotics to prevent spread by drifting diseased bees.

· Shook-swarm method—The queen and adults are shaken into a brand new colony, with new frames and foundation. The hive body, frames with larvae, and pollen and honey stores are all burned. This strategy is not recommended as adult bees may still transport spores in honey from their stomachs. These bees and the remaining colonies in the apiary should be treated with antibiotics to prevent spread by drifting diseased bees.

· Essential oil therapies—While many EOs have been evaluated, none have proven effective at controlling or preventing AFB in colonies in the field long-term.

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Beekeeping management practices that avoid spreading AFB to other colonies and areas is the best preventative measure. Consistently monitor colonies and destroy symptomatic colonies, especially if maintained in high density areas for beekeeping. Infected hives are a major source of infection to neighboring colonies. Wear disposable gloves when working in AFB positive colonies. Disinfect hands and beekeeping tools between healthy and diseased colonies. Do not combine weak colonies with other colonies. Because it is impossible to determine if old equipment is contaminated with AFB spores, burn old frames and scorch the inside of old hive boxes until blackened before reuse.

Propolis from certain sources has been proven effective at controlling AFB naturally, so encouraging propolis collection and deposition within hives may confer a degree of hive immunity for AFB and other diseases. Bacteriophage therapy is a promising prophylactic feed additive against AFB (Broodsafe™) and may be fed to colonies adjacent to infected colonies as a preventative measure and to cure mild to moderate infections once it becomes commercially available.

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European Foulbrood (EFB) is a bacterial infection of brood, caused by Melissococcus plutonius, with a number of other associated organisms contributing to symptoms. The disease is more problematic when the colony is under stress, as healthy colonies can overcome mild to moderate infections. EFB is present worldwide anywhere honey bee colonies are maintained. Though outbreaks in Hawaii are not common, there are no records with regards to incidence and location of outbreaks.

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EFB is spread when larvae consume the bacteria in contaminated brood food or from infected nurse bees. As the bacteria multiplies in the larva’s gut, it competes for food causing death by starvation. Nurse bees reject larvae that demand an abnormal amount of food. The bacteria is transmitted to nurse bees’ mouth parts when they attempt to remove the dead or dying larvae. If an infected bee survives to adulthood, the colony may be further infected by bacteria spread through their feces. Weak colonies infected with EFB may be robbed, which spreads disease to neighboring colonies. Swarms and absconding colonies may move bacteria between regions. Beekeepers accidentally spread bacteria by moving contaminated combs or hive components to non-infected hives, or by feeding healthy colonies infected honey or pollen. EFB is highly contagious and may remain viable for several years in honey, wax, and equipment.

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This disease has recently become increasingly common and difficult to treat on the mainland. Infected larvae move in their cells, so when they die may take on a twisted appearance. In some cases, the larva collapses on itself, turns yellowish-brown, and dries to form a loosely attached brown scale that is rubbery in appearance. There may be a sour smell associated with infections, but this varies between infected colonies because it is the result of other microorganisms associated with EFB.

Diseased yellowed larvae (yellow) that have taken on a twisted appearance, in comparison to pearly whit ehealthy larvae. Dead larvae dry out to form scales (blue). Photo by R. Snyder, beeinformed.org.

Multiple stages of EFB, likely with a secondary bacterial infection. Photo by R. Snyder, beeinformed.org.

Egg laid in a cell with a brown scale at the bottom (left). EFB contaminated royal jelly (right) being fed to first instar larvae (yellow). Note the discoloration compared to uninfected royal jelly (blue). Photos by R. Snyder, beeinformed.org.

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Infected larvae typically do not become ropey. Though experienced beekeepers may identify infection from the smell, positive diagnosis can only be made in a laboratory. Alternatively,  Vita® EFB test kits are just as accurate. Kits can be purchased from beekeeping supply companies. Suspected diseased larvae are ground in the provided vial and a drop of solution placed on the applicator. A blue line will appear at "C" to indicate the test is working. Any line, however faint, at "T" is positive for EFB.

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When infections are mild, treatment is not necessary and a strong nectar flow will help reduce colony stress. For a moderate infection, requeening will break the egg laying cycle and allow the nurse bees time to remove diseased larvae and clean brood-rearing cells.

Antibiotic treatment with oxtetracycline may be used for moderate to severe infections, and this product is labeled for prophylactic use. However, over treating with antibiotics can lead to bacterial resistance. This is only available by prescription from a veterinarian. Residues may appear in bee products such as honey so honey supers should be removed before treating.  

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Maintaining strong and healthy colonies is the best way to avoid colony losses associated with EFB, and reducing the incidence of symptomatic colonies, particularly as EFB is a stress-related disease. Beekeeping management practices that avoid spreading EFB to other colonies and areas is another preventative measure. Changing brood nest temperatures can trigger outbreaks, so avoid removing adult bees, giving extra brood to rear, or prematurely adding extra supers especially during the winter months. As a precautionary measure, brood frames should be replaced on a 3-4 year basis. Ensure colonies have young healthy queens and inspect for EFB at least twice, once in the spring and once in the fall.

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