American foulbrood (AFB) is a lethal disease that affects honey bee larvae, caused by the bacterium Paenibacillus larvae. Once infected, the brood dies during the pupal or pre-pupal phases. When infection spreads extensively throughout a hive’s brood, it weakens the colony, often resulting in its ultimate demise.
Transmission of American Foulbrood
Contrary to what some might think, this disease is not caused by stress and can infect even robust honey bee colonies. Managing your apiary to prevent robbing and drifting behaviors helps limit disease spread. Although American foulbrood does not spread rapidly like some illnesses, its bacterial spores can move between hives, especially through shared equipment or unknowingly transferring infected comb to healthy colonies. If tools used on contaminated hives are not adequately sanitized, they become a common pathway for spreading spores among hives.
Prevalence of American Foulbrood Disease
American foulbrood is widespread across the Americas and is present in every major beekeeping region worldwide. Complete losses of apiaries due to this disease are not uncommon. Identifying and reporting suspected cases to agricultural or beekeeping authorities is crucial for correct diagnosis and management support.
Characteristic Odor of American Foulbrood
A distinctive sulfurous smell, similar to rotten eggs, often emanates from hives infected with American foulbrood. This odor results from the decomposition of dead larvae within the colony and can be a useful cue for beekeepers with a sensitive nose. However, the presence or absence of this smell should not be solely relied upon to confirm the disease.
Signs and Diagnosis of American Foulbrood
Regular inspections provide vital opportunities to spot symptoms of diseases like AFB. This infection disrupts the brood pattern, causing cells to appear irregular with some capped cells showing sunken, dark, or greasy caps. The infected brood inside these cells deteriorates into a brown, semi-liquid substance. Sometimes, worker bees will attempt to remove dead larvae by perforating the affected cells, leaving behind infectious remnants. Besides visual cues, a sulfurous odor from the hive may alert you to an advanced infection, signaling decay within. Although not always definitive, this smell should prompt thorough investigation for various pathogens, pests, or parasites. The dried remains of dead larvae become brittle and are difficult to extract from the cells.
In some instances, you will notice that bees have perforated the afflicted bee brood cells and tried to remove the dead larvae from inside it. The remains of this brood are infectious. When opening up the beehive, you should pay some attention to the smell coming from inside it. In the event that there is an infection of American foulbrood plaguing your honey bee colony, you will smell a sulfurous odor emanating from the beehive. This foul odor should alert you to death and decomposition in the beehive caused by some problem. Even if the odor is not a product of an infection, it should alert you to give the beehive a thorough investigation for the presence of various other bee diseases, pests, and parasite infestations. Dead larval remains turn tough but brittle, and they are difficult to remove from the afflicted brood cell.
Initial Warning Signs
The symptoms described help confirm when AFB has progressed and brood mortality is evident. However, earlier indicators exist and can assist in controlling the infection before it spreads extensively. Early on, infected brood changes from a pearly white to darker shades like brown or black—a stage when the ‘Ropiness’ test can be effectively applied. Furthermore, older infected larvae may have their tongues adhering to the upper cell walls.
- During initial infection, brood color shifts from white to darker hues, and the ‘Ropiness’ test can be conducted to detect AFB.
- Infection in older larvae often causes their tongues to become stuck to the brood cell’s upper walls.
Both strong and declining honey bee colonies are vulnerable to AFB, necessitating inspection of brood combs at least twice yearly, with increased vigilance during spring and autumn. This careful examination involves checking each frame on both sides and inspecting every cell—capped or uncapped—for signs of the disease.
Early outbreaks may only affect a few brood cells, so it’s important to closely monitor for subtle signs and deformities. Detecting AFB promptly enables management while the colony still maintains a sufficient adult bee population.
Severe Infection Stage
When AFB reaches advanced stages, significant brood mortality leads to a rapid reduction of adult bees, which can ultimately kill the colony if untreated. A strong sulfurous odor is a hallmark of severe infection and extensive colony damage at this point.
Detecting American Foulbrood Using the Ropiness Test
When American foulbrood disease is suspected, a diagnostic test is essential to confirm that the infection is not caused by another brood disease. The Ropiness test is considered the most effective method for differentiating this disease, even distinguishing it from European foulbrood.
To perform the Ropiness test, you need to access the suspected comb, which involves opening the beehive and removing a frame. Appropriate protective gear should be worn if bees are present, and a hive tool is necessary for lifting the frames. It’s important to handle the frames and comb carefully to avoid damaging the comb and compromising hive cleanliness, even if the comb is infected.
Performing the American Foulbrood Ropiness Test
Select honeycomb cells that have not yet hardened into the ‘scale’ phase for testing. Gently insert a matchstick into the suspect cell and then slowly withdraw it.
If the remains of the dead brood cling to the matchstick in a somewhat fluid state, forming a thread between 3 and 5 centimeters in length, it indicates a possible case of American foulbrood. The fluid being dark brown further supports this diagnosis.
Following the Ropiness test, observing where brood death occurs in the hive can help differentiate between foulbrood types. American foulbrood typically kills larvae after cell capping, while European foulbrood usually causes larval death before capping.
Additional Uses of the Ropiness Test
The Ropiness test can also be applied to other honey bee brood diseases such as European foulbrood. For infections caused by Melisococcus plutonius, the resulting thread from infected larvae is relatively short—about 1.5 to 2 centimeters. However, infections caused by Paenibacillus alvei may produce longer threads that could be mistakenly identified as American foulbrood caused by Paenibacillus larvae.
Is the Ropiness Test Conclusive?
While useful, the Ropiness test alone is not definitive. It should be followed by laboratory analysis to confirm the presence of American foulbrood. Additionally, some regions mandate reporting this disease to agricultural authorities.
It is advisable to inform neighboring beekeepers if you encounter American foulbrood so they can monitor their colonies more closely. Likewise, increased alertness is warranted if other local beekeepers report confirmed cases.
Treating American Foulbrood
Managing American foulbrood involves both preventive actions to avoid infection and treatments to restore hive health when the disease occurs. If prevention fails, treatment is necessary to revive the colony.
Antibiotic Treatments
Chemical treatment is one approach to controlling American foulbrood, sometimes used alongside preventative measures. Certain antibiotics can help manage the disease, although their use may be restricted or banned depending on local regulations. It is crucial to consult agricultural authorities regarding their permitted application.
Antibiotics commonly used include Oxytetracycline Hydrochloride (Terramycin) and Tylosin Tartrate, the latter approved by the U.S. Food and Drug Administration in 2005.
While these antibiotics do not eliminate Paenibacillus larvae spores, they help slow disease progression within the hive. However, their residues can contaminate honey, and improper use has contributed to the emergence of antibiotic-resistant strains of the disease.
Hygienic Practices
The natural hygienic behavior of honey bees plays an important role in resisting American foulbrood. Bees that efficiently uncap infected cells and remove dead larvae can limit the spread of spores, reducing infection. Certain bee strains exhibiting these behaviors demonstrate some tolerance to the disease.
Nevertheless, even colonies with strong hygienic traits will succumb to American foulbrood without intervention, as repeated reinfections weaken the hive over time.
Managing a Beehive Infected with American Foulbrood
When American foulbrood is detected, saving the colony is often challenging. Irradiation of the hive and its contents can destroy the bacteria and spores, but this service may be inaccessible or costly for many beekeepers. If irradiation isn’t an option, the recommended practice is to seal the hive entrance, ensure all bees are inside, then burn and bury the entire hive and colony deeply to prevent disease spread.
To salvage part of the hive, frames and comb may be burned while hive boxes and other parts are thoroughly scorched to kill bacteria and spores. Prolonged exposure to ethylene oxide gas in a sealed chamber effectively sterilizes spores. Additional cleaning methods include washing with 3% sodium hypochlorite or dipping hive components in hot paraffin wax.
New Approaches to Treating American Foulbrood
Innovations in beekeeping science are offering promising strategies for controlling American foulbrood. Advances in epidemiology and microbiology have led to experimental treatments such as phage therapy and biological control.
Phage Therapy
Phage therapy employs viruses that specifically attack bacteria. Introducing bacteriophages targeting Paenibacillus larvae into infected hives could potentially eliminate the disease. Research is ongoing to optimize this approach.
Biological Control
Biological control uses beneficial bacteria to suppress Paenibacillus larvae. Certain lactogenic bacteria have shown strong competition against the foulbrood pathogen in lab settings. However, reliable success in treating infected hives under field conditions has yet to be demonstrated.
Sanitizing Beehives Following American Foulbrood Infection
When a beehive becomes infected with American foulbrood disease, thorough cleaning and treatment of the hive are essential. The spores of Paenibacillus larvae can remain infectious for decades, with viability documented for over 50 years, and they resist both freezing and heat. If these spores are not properly eliminated from the hive, the disease can resurface. To prevent recurrence, adopting optimal beekeeping management practices is crucial, along with rapid sanitation and cleaning before the infection spreads to neighboring hives.
Tools and equipment used in managing beehives can serve as vectors for the spread of American foulbrood spores. In an apiary with multiple hives, it is vital to routinely sanitize all instruments before moving between hives. This practice acts as an effective barrier against transmission of diseases, pests, and parasites. Strong disinfectants like bleach are commonly employed, as they are both effective and safe for the tools used in beekeeping.
Preventing American Foulbrood Disease
Beekeeping places great importance on preventing disease outbreaks, particularly preventing American foulbrood spores from infiltrating your hives. Both novice and experienced beekeepers need to prioritize prevention, integrating it carefully into their routine hive and apiary management strategies.
The extent of spore contamination entering a beehive influences how rapidly American foulbrood can spread within the colony. Maintaining strong colony management practices restricts the disease’s ability to gain entry or proliferate quickly. Conducting regular inspections of the brood comb is essential for early detection; ideally, the entire comb should be examined at least twice yearly.
Comb Management
Old brood comb can harbor spores of American foulbrood and act as a long-term source for low-level infections. To minimize this risk, beekeepers routinely remove aged comb and allow bees to construct fresh comb. Every three to four years, brood boxes should be cleared of old comb. This comb may then be repurposed for honey storage in supers and harvested, after which it is suitable only for honey storage, beeswax extraction, or disposal.
Limit Equipment Interchange
Reducing the sharing of materials and equipment between hives is an effective way to limit disease, pest, and parasite transmission within an apiary. When equipment must be used between different hives, thorough cleaning is critical. Methods such as scorching or treating tools with washing soda and bleach effectively eliminate microorganisms and contaminants, helping to prevent honey bee diseases from spreading during routine handling.
Barrier Management System for American Foulbrood Prevention
A barrier management approach, used in large apiaries, divides beehives into smaller groups managed collectively. Equipment may be shared within each group but not beyond it, which helps contain diseases, pests, and parasites within a confined cluster should an outbreak occur. This method enhances biosecurity, traceability, and quality assurance, representing a major advancement toward maintaining high standards in beekeeping practices.
American Foulbrood Test Kit
Commercially available test kits allow rapid detection of American foulbrood, delivering results in about three minutes. These kits provide laboratory-grade accuracy, serving as reliable confirmation of infection within a hive. If desired, additional testing can follow the initial kit-based diagnosis. Note that each test kit is designed for a single hive and should be discarded after use; separate kits are required for multiple hives.
Vaccine and Cure
Currently, no vaccine or cure exists for American foulbrood disease, though ongoing research offers encouraging prospects for future treatments and preventive vaccines.
Scientific studies are exploring ways to inhibit the germination of Paenibacillus larvae spores even after they enter the gut of honey bee larvae. Researchers introduce harmless compounds into the hive, ensuring that these substances are fed to the developing brood.
In experimental trials, larvae that received this treatment were able to withstand exposure to bacterial spores. Before this method can be widely adopted, researchers aim to optimize the delivery system and identify the most effective compound to prevent American foulbrood infections.
Conclusion
Maintaining cleanliness and strict hygiene within the beehive and apiary is key to preventing diseases such as American foulbrood from establishing and spreading quickly. After an infection, heightened vigilance is necessary, along with regular, systematic cleaning of hives to ensure safety. Because American foulbrood is contagious, it can easily transfer between apiaries if not carefully managed.
Applying both preventative and active control strategies is essential to minimizing losses in your honey bee colonies due to American foulbrood infection. Beekeepers have access to a variety of tools and methods for effective management and treatment. Choosing the best approach involves balancing results with financial viability to maintain sustainable beekeeping operations.