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American Foulbrood 1: What is it and How is it Spread?

A dreaded brood disease, American Foulbrood can devastate a hive and is easily spread

Brood diseases are numerous and nasty, but one of the nastiest has to be American Foulbrood. Caused by a bacterium that multiplies and spreads via some very tenacious spores, it’s one of the least pleasant surprises a beekeeper can find in their beehive.

American Foulbrood: What is it and why is it a problem?

  • American Foulbrood (AFB) is a highly infectious, bacterial honey bee brood disease
  • All Australian states report the presence of American Foulbrood, except the Northern Territory
  • It can infect both weak and strong colonies, hive stress is not a factor
  • AFB kills honey bee larvae and pupae but not adult bees
  • AFB does not affect humans. Honey that contains AFB spores is safe for humans to eat
  • Infection of bee larvae happens when they ingest spores of the bacterium Paenibacillus larvae
  • Usually the larva dies immediately after adult bees cap the brood cell. Occasionally it dies later, at the pupal stage
  • The bacterium begins to multiply rapidly after capping. Spores germinate to form vegetative ‘rods’
  • It reaches the final stage of its lifecycle when the rods form into many new spores
  • Through this process dead larvae becomes dried scales that stick to the side of the cells
  • There about 2,500 million American Foulbrood spores in the remains of a single infected bee larva
  • Through rapidly infecting and killing brood, especially during the spring build up, AFB can significantly weaken or even destroy a honeybee colony

How is American Foulbrood Spread?

  • American Foulbrood spores remain active for about 50 years or longer
  • They are resistant to heat, freezing, direct sunlight, dehydration, fermentation, many chemical disinfectants and therapeutic drugs
  • Infections start when nurse bees spread spores on their mouthparts to larvae through feeding
  • A bee larva less than 24 hours old is most susceptible, as few as 10 spores cause an infection
  • The disease cycle of AFB means that once spores reach the brood the bacteria can multiply very fast
  • Inside the hive, nurse bees continue to spread spores when they clean infected cells and attempt to remove dead pupae
  • Field bees can also spread spores within and between hives through robbing and drifting behaviour
  • As AFB weakens infected colonies, these hives become easy targets for robbing bees
  • Beekeepers can spread the bacterial spores if they place infected combs or hive components in non-infected hives
  • Spread of spores can also occur on tools and equipment
  • Re-feeding infected honey and pollen to bees will also spread infection
  • Swarms and absconding colonies can spread the disease between areas, but this is less common

Next week on The Buzz we take a look at identifying (diagnosing) and managing Amercan Foulbrood in your hive.

Sources:

BeeAware – American Foulbrood

Rural Industries Research and Development Corporation – Australian Beekeeping Guide

American Foulbrood picture of scattered brood comb

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