American Foulbrood (AFB)

In a colony heavily infested with AFB you will see moisture on the sealed brood.  You will also see brood oozing from perforated cells at this stage.

In a colony heavily infested with AFB you will see moisture on the sealed brood. You will also see brood oozing from perforated cells at this stage.

How does AFB spread? American Foulbrood (Paenibacillus larvae) is introduced to the hive by drifting bees from nearby colonies, infected equipment/tools, beekeepers and robbing. The infection begins when spores enter the hive, and then food contaminated by spores is fed to the larvae by nurse bees. Once spores are in the midgut the bacteria take over using the larvae as a source of nourishment. After the cells are sealed, death occurs. If death occurs while in the pupal stage, there may be a protruding tongue present. When there is a serious infection you can notice moisture on sealed brood as they start to sink. Sunken sealed cells are a result of decomposing larvae. AFB is very contagious and all equipment must be cleaned before using it in healthy hives.

The AFB scale is very hard for the bees to remove and can infect colonies for years to come. This is why some states have a “burn only” policy, but others allow the use of antibiotics to control the disease. It is important to have the AFB tested by a lab (USDA Honey Bee Lab) to identify if the AFB strain is resistant to Terramycin (oxytetracycline hydrochloride).

American Foulbrood (AFB)

American Foulbrood (AFB)

Symptoms:
• Spotty brood pattern, perforated sealed brood with coffee brown larvae inside, sunken sealed brood, coffee brown larvae sunken to the bottom of the cell.
• Moisture on sunken sealed brood, protruding pupal tongue (rare), and rotting smell (compared to rotting meat or sulfurous chicken house).
• Light to dark brown to black scale that is hard to remove.
• Often colonies next to infected colonies will show symptoms of the disease.
• Larvae rope at least 2 cm.

AFB: Symptoms in open brood.

AFB: Symptoms in open brood.

Treatment:
It is best to burn all colonies infected with AFB but you can treat infected colonies with antibiotics. There are two antibiotic treatments for AFB: Terramycin and Tylan. If AFB is not resistant to Terramycin (oxytetracycline hydrochloride) then this antibiotic is used. If the strain of AFB is resistant to Terramycin, than Tylosine is the antibiotic used to treat the colony. Treating colonies 8 weeks prior to the nectar flow is recommended to prevent honey from being contaminated.
Note: Tylan is supposed to be used once symptoms occur in the hive because it leaves behind residuals for far longer than Terramycin. Terramycin is the only antibiotic that can be legally used prophylactically.

This is often how I will see AFB in a colony.  Most of the open brood has been removed by the bees.  But you will still find ropy larvae/pupa under perforated seaed brood.

This is often how I will see AFB in a colony. Most of the open brood has been removed by the bees. But you will still find ropy larvae/pupa under perforated seaed brood.

AFB: Scale forming in cells

AFB: Scale forming in cells

American Foulbrood (AFB) Deadout.

American Foulbrood (AFB) Deadout.

Written By: Rob Snyder

Rob Snyder has written 62 post in this blog.

I currently work out of the Butte County Cooperative Extension in Oroville, CA as a Crop Protection Agent. I received my B.S. in biology from Delaware Valley College, PA. There I attained a majority of my entomological knowledge from Dr. Chris Tipping and Dr. Robert Berthold. After graduation, I was an apiary inspector for 2 years at the Department of Agriculture in Pennsylvania. In my third year there, I still inspected some colonies but I mainly focused on The Pennsylvania Native Bee Survey (PANBS) where I pinned, labeled, entered data and identified native bees to genus species. Leo Donavall assisted me in learning the basics on positive Identifications of the native bees. Around the same time I began working on coordinating kit construction and distribution for the APHIS National Honey Bee Survey. I was also fortunate to conduct many of these surveys with fellow co-worker Mike Andree and Nathan Rice of USDA/ARS throughout California. All of these experiences have led me to where I am today, working to assist beekeepers in maintaining genetic diverse colonies resistant to parasites while reducing the use of chemical treatments in colonies. The BIP Diagnostic Lab at the University of MD is in an integral part of this process by generating reports in which we can track change and report to beekeepers vital information in a timely manner which may influence their treatment decisions.

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