American foulbrood

What is it?

American foulbrood is a serious bacterial disease that affects the brood of honey bees. It is considered one of the most destructive diseases for apiaries because it gradually weakens and then destroys colonies. It is a notifiable disease in many countries due to its severity.

Commonly observed signs

These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.

Causes and risk factors

The disease is caused by the bacteria Paenibacillus larvae, which forms extremely resistant spores. These spores are ingested by young larvae during feeding, which triggers infection. The bacteria then grows inside the larva, causing it to die.

Sharing undisinfected beekeeping equipment between apiaries greatly increases the risk of contamination. A high density of hives, pillaging between colonies and the introduction of swarms or queens of unknown origin are also contributing factors. Conditions of stress or weakened colonies can also make bees more vulnerable.

Transmission

Transmission occurs mainly through very resistant bacterial spores, present in honey, wax or contaminated materials. Worker bees spread the disease by cleaning infected cells and feeding healthy larvae. Plundering between hives and the exchange of contaminated beekeeping equipment also encourage the 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.

Prevention

References

WOAH — Organisation mondiale de la santé animale (ex-OIE)

Content reviewed by the TunisieVet editorial team · Updated 18 August 2026