Honey Testing for American Foulbrood Explained
- Joe Varey, Hill Labs
- May 2
- 3 min read
It is now one of the most common tests which honey samples in New Zealand undergo, for both reasons of controlling spread of the disease and market access requirements. So how does testing for American foulbrood (AFB) work and how accurate are the results?
AFB is a bacterial disease that affects honey bee larvae and pupae, causing them to weaken and eventually die. Paenibacillus larvae (the bacteria responsible for AFB) form spores that are highly resistant and survive for long periods of time. The spores are very easy to transmit and can contaminate honey, pollen and beekeeping frames, boxes and processing equipment.
As AFB is listed under the Biosecurity Act 1993 as a risk, there are obligations that beekeepers must comply with. The AFB Management Agency provides all guidance regarding regulations, management of the disease and steps to be taken if you find it within your colonies.
Clinical identification of the disease has traditionally been carried out by visual inspection of the brood, and continues to be. However, now with fast turnaround Polymerase Chain Reaction (PCR) methodology, positive/negative detections can be returned as fast as same-day from the lab, allowing for sub-clinical (non-visual) diagnosis.
The industry standard limit of reporting for AFB is 92 or more spores and/or cells per gram detected. Anything above this limit of reporting will flag your honey as AFB positive. Lab reports show an estimation of the spore count if a positive result is returned, however this estimation is an indication only. Because PCR works on amplification of DNA, the spore count is a calculation based on how many cycles the PCR took to find a quantifiable amount of the target DNA.
It is a well-known phenomenon that low level positive results that hover around the limit of reporting can sometimes return a ‘not detected’ result on a re-test. The lab uncertainty of measurement plays a big role in reproducibility of results and at low levels, a second result can return a ‘not detected’ reading. The typical range of uncertainty is +/- 1.5 Cq on any result. In terms of a spore count, the uncertainty will vary depending on the concentration of the bacteria. It’s important to consider this when understanding your lab report. For more information on the uncertainty of measurement it is best to contact your lab provider, who can talk you through what the acceptable range is for a spore count on any result.
If a positive result is returned to any degree in a sample, it can be trusted as true and correct. PCR only selects and amplifies the DNA that it is looking for, meaning positive results are true and correct, with little chance of interference. Any other DNA in the sample will not flag positive results, as the PCR is highly specific and will only detect AFB if present. Positive results are compared against known concentrations of an internal standard. Known levels of the target DNA are run alongside all live samples.
Every batch of samples run through the laboratory includes multiple quality control mechanisms to prove that any levels of the disease found are accurate and prove that no contamination can be found in any stage of the process. Automated processes prompt repeat analysis when internal quality controls are not met, meaning results are only released once stringent quality checks are met on every live sample.
Testing honey for AFB is widely recognised as a requirement when your product is being shipped to China. The China Overseas Market Access Requirements (OMAR) specifies that any honey arriving at the border may be subject to a lab test for the disease.
Whilst finding AFB spores in your honey is also an indication the colony carries the disease and can play a role in decision making regarding blending and refeeding the honey back to the bees (which best-practice to avoid disease transfer would always advise against), there is currently no data on what level of AFB bacteria or spores need to be present in a honey sample to indicate there would be clinical signs of AFB in a hive. For this reason, using honey results can be a tool in your arsenal against the disease – but it should be far from your only approach.
There are resources available to help you with monitoring for AFB. Some helpful links are:
For more information regarding honey testing, get in touch with your local laboratory testing provider.
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