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American foulbrood
American foulbrood is a serious bacterial disease affecting honeybee brood. It is considered one of the most destructive diseases for apiaries because it progressively weakens and destroys colonies. It is a notifiable disease in many countr...
What is it?
American foulbrood is a serious bacterial disease affecting honeybee brood. It is considered one of the most destructive diseases for apiaries because it progressively weakens and destroys colonies. It is a notifiable disease in many countries due to its severity.
The disease is caused by the bacterium Paenibacillus larvae, which forms extremely resistant spores. These spores are ingested by young larvae during feeding, triggering the infection. The bacterium then multiplies inside the larva, leading to its death.
Sharing undisinfected beekeeping equipment between apiaries greatly increases the risk of contamination. High hive density, robbing between colonies, and introducing swarms or queens of unknown origin are also contributing factors. Stress or weakened colony conditions can also make bees more vulnerable.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Signs include an irregular capped brood pattern, with sunken, perforated or darkened cell cappings. Dead larvae become brownish, ropy and sticky, giving off a characteristic unpleasant odor. Over time, larvae dry into a dark scale that is hard to remove from the cells.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Transmission
Transmission occurs mainly through highly resistant bacterial spores present in honey, wax or contaminated equipment. Worker bees spread the disease while cleaning infected cells and feeding healthy larvae. Robbing between hives and the exchange of contaminated beekeeping equipment also promote spread between colonies.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
There is no reliable curative treatment that can save an infected colony without risk of spreading the disease. Any suspicion of American foulbrood should be reported promptly to the relevant veterinary or beekeeping authorities. Only a veterinarian or official beekeeping service can confirm the diagnosis and advise on the appropriate course of action.
Prevention
Prevention relies on good beekeeping hygiene, such as regularly disinfecting equipment and avoiding sharing tools between apiaries. It is important to regularly monitor brood condition to detect any abnormal signs early. If suspected, it is essential to report the situation to the relevant veterinary authorities and consult a qualified veterinarian or beekeeping technician.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
Content reviewed by the TunisieVet editorial team · Updated 08 August 2026
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This information is provided for educational purposes only and is not a substitute for a veterinary consultation. If you have any concerns about your animal's health, consult a veterinarian.