Foulbrood and the notifiable bee diseases

Three lists, three meanings

'Notifiable' is the word beekeepers meet, and it hides three different kinds of list. The World Organisation for Animal Health lists diseases that countries report internationally and that trade standards address. The European Union sorts its listed diseases into categories, each triggering different measures. England makes some diseases and pests notifiable, which places a legal duty on anyone who suspects one to report it. The lists overlap without matching.

Two mismatches are worth noticing. European foulbrood is listed by WOAH and notifiable in England but is not in the EU list at all. Varroosis is listed by WOAH and by the EU, and is the only bee disease in category C, the category for protecting parts of the Union that are officially free of a disease or running eradication programmes — yet it is not notifiable in England, where it is established and a duty to report every case would serve no purpose.

American foulbrood

American foulbrood is a disease of the larva, caused by the bacterium Paenibacillus larvae, and it occurs throughout the world. It is the most feared of the brood diseases because of its spores. A single infected larva can produce more than a billion of them; they are extremely resistant to heat and chemicals; and only the spores cause infection.

• Larvae can be infected only in the first 53 hours after hatching, and the median infective dose in day-old larvae is around eight spores.
• Spores survive 3 to 10 years in honey, wax and dead larvae, 35 years in the dried scales of dead brood, and more than 70 years when purified.
• Exchanging combs that carry diseased brood is the commonest route between colonies; feeding or robbing spore-laden honey or bee bread, packages, queens and badly treated foundation wax also spread it.
• The signs are variable: a mottled brood pattern, sunken, darkened and perforated cappings, larval remains that draw out in a brown rope, and finally brittle scales stuck to the cell wall.
• There are no vaccines, and no serological tests; diagnosis rests on identifying the bacterium.

European foulbrood

European foulbrood is caused by a different bacterium, Melissococcus plutonius, and is harder to see. The usual sign is larvae dying shortly before their cells are due to be sealed — but larvae die then for other reasons too, and most infected colonies show few visible signs. The WOAH diagnostic standard says field recognition is unreliable without specialist training. Because the organism contaminates the comb, infection tends to persist within a colony and recur in later years. It is widespread and, in some areas, an increasing problem.

The tracheal mite

Acarapisosis is caused by Acarapis woodi, a mite about 150 micrometres long that lives and breeds inside the breathing tubes of adult bees, feeding on their blood. Bees are most susceptible in their first four days after emerging. Heavy infestation blocks and damages the tracheae; light infestation usually goes unnoticed, and the mite can be found only in the laboratory. Some strains of bee are less susceptible than others. It is listed by WOAH but is neither in the EU list nor notifiable in England.

Nosema, or Vairimorpha

Two single-celled parasites of the adult bee gut, long known as Nosema apis and Nosema ceranae, are not listed by WOAH, the EU or England. Their name is itself in dispute. In 2020 a group of microsporidia specialists moved them to the genus Vairimorpha on molecular evidence; in 2024 bee pathologists from Spain, the United States Department of Agriculture and China argued that the revision was flawed and that Vairimorpha should be merged back into Nosema. HoneyHQ uses both names until the question settles, because a reader will meet both.

What reporting means in practice

Where a disease is notifiable, the duty is to report a suspicion, not to diagnose it. In England that report goes to the National Bee Unit, whose inspectors confirm the diagnosis and decide what happens to the colony. This guide deliberately describes the diseases and the law and stops short of treatment or control, which are the authority's to direct.