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American and European Foulbrood
By: Mary Reed
I grew up in a rural part of Florida with parents who allowed their children to roam the great outdoors on their own. I have many memories of trekking through the woods with my siblings, our pack of dogs trailing us wherever we went. Whenever we returned from our great adventures, we would comb over each dog to check for any ticks or other critters that may have hitched a ride back to the house. It became a customary part of country living to constantly be on top of any pest or disease that may show up on our dogs or any one of our other farm animals. As beekeepers, we also have a lengthy list of pest problems that can wreak havoc in a colony, and we have to be diligent about managing all of them so we don't end up with sick bees. If you have ever heard me give a presentation before, this is where you are expecting me to step onto my Varroa mite-shaped soap box and talk about how the bees need you to manage the mite levels in their hives.
Unfortunately (or fortunately?) you are mistaken this time. I'm going to step onto a different box this time and talk about the two types of foulbrood diseases every beekeeper has the potential of encountering at some point in their beekeeping career. Between these two diseases, there is one that is bad and then there is one that is worse. So, let's dive right in and start with the worst kind of foulbrood you could encounter.
American Foulbrood (AFB) (Paenibacillus larvae) is considered to be one of the most problematic diseases to afflict a honey bee colony and the industry as a whole. At one point AFB was so widespread and so damaging to the apiary industry that it is the reason states established apiary inspection programs in an effort to control the disease. Fortunately, these programs were largely successful in their efforts, but it is still considered a threat to the industry and is monitored by all inspection programs.
Okay, so why is this disease such a big deal? The main issue with this disease is that it is a spore-forming bacterial infection that infects the developing brood. The key factor to understand about this disease is that the bacteria generates spores. These spores can remain viable in honey, wax, and equipment for decades and can cause issues for a hive once they become activated. A developing honey bee larva is typically infected by being fed AFB-contaminated brood food. The bacteria will replicate in the larva's midgut and the larva will die soon after it has been capped over. Sometimes death will not occur until the larva has reached the pupal stage.
Sunken, punctured, moist cappings of AFB Photo Credit: Rob Snyder/Bee Informed Partnership
American Foulbrood is an extremely contagious disease and can be spread through robbing of infected colonies, drifting of diseased bees, and the transfer or use of infected equipment and tools. Unfortunately, the only effective treatment for this disease is to burn the entire hive, including the bees. If you do additional reading on this disease, you may come across suggestions to use an antibiotic treatment to prevent AFB. Many beekeepers in the past have treated their hives prophylactically with antibiotics to suppress this disease.
In recent years there have been developing concerns about the overuse of antibiotics in animal agriculture, so changes have been made to federal law that now require beekeepers to work with a veterinarian in order to acquire an antibiotic for their honey bee hives. Regardless of these changes to the law, the use of antibiotics should be your last choice. Antibiotics will not rid a hive of AFB, it will only suppress the disease. There is an increasing concern about the development of antibiotic-resistant bacteria, and the overuse of antibiotics in the apiary industry can lead to (and there is already evidence of this occurring) ineffective antibiotics for foulbrood diseases. For more information about antibiotic use in honey bee colonies, I encourage you to check out the Honey Bee Health Coalition's guide to managing foulbrood in honey bee colonies.
Okay, so we know this disease is bad, but how will you know if your hive is infected? The key with identifying AFB is to look at the brood cappings. This is the only disease where you will see symptoms on the cappings. First, the brood cappings will look sunken in, may have tiny pinprick holes, and may even look like they are sweating. You may also see some symptoms in the developing larvae, primarily discoloration. Healthy larvae will look pearly white, however AFB-infected larvae will turn a brown to black color. Another symptom you may see is what is commonly called a "pupal tongue."
Pupal tongue Photo Credit: MAAREC
This pupal tongue forms when an infected pupa degrades and starts to melt to the bottom of the cell. As it melts, it starts to dry out, and part of the pupa stays stuck to the top of the cell, creating a vertical "tongue" near the entrance of the cell. You may also find a hard scale formed at the bottom of the cell. Scales form when infected brood have decayed and dried out in their cells. A defining characteristic of AFB is that this scale is nearly impossible to remove from the cell once it has dried. When looking for scale, holding a frame up to your face will not help you spot them. Instead, hold the brood frame by the top bar, turn to face the sun, and hold the frame about hip-height with the sun hitting the wax comb. This allows you to see down into the bottom of the brood cells and properly inspect for scale.
AFB scale formed at the bottom of a brood cell. Photo Credit: Bee Informed Partnership
Another symptom of AFB is a spotty brood pattern. However, it's important to remember that a spotty brood pattern can be caused by a multitude of pest, disease, or other health issues. If you notice a spotty brood pattern in you hive, don't jump to conclusions! Look for other symptoms within the brood area to see if you can narrow down what the exact issue is. So, we have all of these symptoms and let's say you stick your head in your hive one day and you are concerned that it may be infected with AFB. How can you determine if it is actually AFB or not?
First, there are a couple of in-field tests that you can conduct:
1.) the rope test and
2.) a Vita in-field AFB test.
For the rope test, all you need is a toothpick, twig, or a small stick of some sort. Insert the stick into the suspected larval cell, swirl it around, and then slowly draw the stick out. If the larval goop remains attached to both the stick and cell, and draws out more than 1.5 centimeters, then most likely the hive is infected with AFB.
American Foulbrood rope test Photo Credit: Vita Bee Health
As an additional test, you can purchase an in-field test, made by Vita, from a beekeeping supplier. This test comes with all of the tools you need to sample your hive and get results in a matter of minutes. Your other option is to collect a sample and send it to the USDA Bee Research Lab in Beltsville, MD. They will process foulbrood samples for free and have instructions on their website on how to collect and ship your samples.
Please keep in mind that if you suspect or determine your hive(s) have AFB, you are required under the current Texas beekeeping laws to report it to my office, the Texas Apiary Inspection Service. In these situations, we work with the beekeeper to set up an emergency inspection to determine if the hives are infected. We are able to conduct an in-field test, as well as collect samples for additional analyses if needed. If the hives turn out to be positive for AFB, we work with the beekeeper to mitigate the disease in their operation.
So, we have the symptoms down, we know how to test for it, now how do we prevent AFB from ever becoming an issue? First of all, make sure to sanitize your beekeeping tools on a regular basis, especially if you work with other beekeepers' hives. What this entails is washing your suit, cleaning your gloves (or even better replacing them), heat-treating your hive tools, and cleaning any other tools you may use. Another good practice is rotating out old comb from your hives every few years. Also, remove any frames from unknown sources as soon as possible. If you purchase nucs or hives, sometimes beekeepers will include old frames as a way to rotate out their old equipment. Since you are not intimately aware of the ins and outs of that beekeeper's operation, or what the origin story of that equipment is, it's good practice to get those frames out of your operation and have your bees build fresh comb.
In addition, do not feed your bees honey if you do not know its original source. What I mean by this is do not buy honey at the store and dump it into your feeder. The frames of honey in a hive or Nuc that you purchase is fine to keep, as long as you are not seeing symptoms of disease. And finally, do your best to prevent your hives from robbing other colonies in the area. Make sure your hives have the resources and stores they need throughout the year, especially during resource dearth, so they don't go scavenging in other hives.
European Foulbrood Alright, that's one foulbrood down (phew!), let's move onto the second! European Foulbrood (EFB) (Melissococcus plutonius) is considered to be the lesser of two evils when it comes to foulbrood diseases. There are a few similarities between AFB and EFB, but there are key distinctions that help beekeepers distinguish between the two. First of all, EFB is also a bacterial disease, however this bacteria does not generate spores. This is a really important factor to remember when it comes to understanding the biology, spread, and treatment of this disease. Since EFB does not generate spores, there is less of a concern about it sticking around for decades in wax, honey, and equipment. However, that doesn't mean that the sanitary practices mentioned earlier for AFB aren't also good practices in preventing and controlling EFB. Before we dive too far into prevention and treatment methods of EFB, let's first talk about how it infects a colony and the symptoms that may show up as a result.
When a hive becomes infected with EFB, the bacteria spreads and proliferates through the developing larvae. The bacteria is ingested by a developing larva when it is fed contaminated brood food. The bacteria then starts to compete with the larva for food and the larva will typically die when it is 4-5 days old. Now that we know what stage of development EFB affects, we can safely assume that symptoms of disease will show up at the larval stage. This is a key difference between identifying EFB versus AFB! Remember, AFB symptoms typically show up in the brood cappings. Whereas symptoms of EFB show up in the larvae that have yet to be capped over.
Tracheal system visible in EFB-infected larvae.Scale is beginning to form. Photo Credit: Rob Snyder/Bee Informed Partnership
Another key symptom of an EFB infection is that larvae will appear discolored (yellow to brown color) and look like it is twisting up towards the entrance of the cell. Sometimes you can even see the white trachea within the discolored larva. Other symptoms include an odor, larvae melting to the bottom of the cell, spotty brood pattern, and a scale that forms at the bottom of the cell. As opposed to the scale that forms with AFB, the EFB scale is brittle and can easily be removed. Just like for AFB, there are several options beekeepers have when it comes to testing for EFB. Most of the testing resources overlap with those mentioned for AFB. If you choose to use one of the Vita in-field diagnostic tests, make sure you use the one specifically designed for EFB. It is important to note that the rope test will not work for EFB. If you were to attempt the rope test for an EFB infected larva, the larval goop will not extend out as far and it will not remain stuck to the cell.
EFB-infected larvae twisting in the cell. Image shows comparison between infected larvae and healthy larvae. Note there are no symptoms exhibited on the brood cappings. Photo Credit: Rob Snyder/Bee Informed Partnership
As for methods of prevention, some of the tactics overlap with preventing AFB, such as rotating out any old or unknown equipment, sanitize your beekeeping tools regularly, and do not reuse any equipment from a hive that was known to be infected with EFB before. In addition, make sure your hives are well fed and that they have a strong worker population to properly care for the brood. Hives often encounter issues with EFB in situations where there are sporadic nectar flows and/or there are not enough nurse bees to care for the developing brood. If you determine your hives have EFB, there are a few treatment options that will help clear up the disease.
A good first step is to feed your hives sugar water and keep feeding them until they either get on a good nectar flow, or you find that the disease has been cleared out of the hive. Another step that you can take either in conjunction with feeding sugar water, or as a follow-up to feeding, is to re-queen your hives, ideally with a hygienic queen. This will help create a brood-break, as well as integrate hygienic workers that can better manage disease within the hive. If after taking both of these steps, you are still seeing symptoms of EFB, then you may need to consider using an antibiotic treatment. Remember, you will need to work with a veterinarian in order to acquire an antibiotic treatment and this should only be used as a last resort. Unfortunately, these two diseases can be found across the nation, as well as worldwide.
In Texas, we do not find AFB very often. In fact, the last reported positive case was about 7 years ago. Although we have not had a positive case in several years, that does not mean that the disease does not exist in Texas. It's important for beekeepers to be able to recognize the symptoms and take the appropriate measures to prevent the disease from spreading. As for EFB, we find this disease primarily in the spring time. However, in the past year we saw more cases of EFB show up in the fall. More often than not, when we receive reports of AFB or EFB it turns out to be a Varroa mite issue instead (Parasitic Mite Syndrome).
There are several symptoms expressed from high Varroa mite populations that can look very similar to symptoms of foulbrood disease (i.e., melting larvae, discolored larvae, spotty brood pattern). This is why it is critical to understand the symptoms of all three situations, ask questions to make sure you are correctly diagnosing the issue, and know what resources to use to confirm your suspicions. In order to help with this, my office has developed a document that covers AFB, EFB, and Parasitic Mite Syndrome.
The website BeeMD is also an excellent tool to use when you are attempting to diagnose any issue (outside of foulbrood disease) that you are seeing in your hives.
AFB Spore-forming, Symptoms affect capped pupae, Scale forms at bottom of cell –difficult to remove, Assess cappings for symptoms, Rope test.
EFB Non-spore-forming, Symptoms affect young larvae, Scale forms at bottom of cell –easy to remove, Assess uncapped larvae for symptoms, No rope test.
As always, I encourage every beekeeper to reach out to my office if they are concerned about something they are seeing in their hives (979-845-9713; firstname.lastname@example.org). We are happy to answer any questions, analyze pictures of the issue, and come out to do an inspection if needed - Mary Reed