European Foulbrood larvae turning into scale, also note the two cells with contaminated brood food.
The most problematic pest beekeepers encounter in the United States today is the varroa mite. The varroa mite (Varroa destructor) is an ectoparasite associated with spreading disease, pathogens and reducing the lifespan of male and female honey bees. The mites accomplish this by creating wounds in honey bees with piercing/sucking mouthparts, then feeding on the hemolymph within. Research suggests that these mites transfer single-stranded RNA virus between bees, along with infections of bacteria, including Melissococcus pluton (EFB). This type of bacterial infection of larvae or pupa is considered a secondary infection, since the mite initiated the process and the bacteria followed.
PMS or parasitic mite syndrome is different than EFB and can easily be confused. I think it is possible for both of these problems to occur at the same time. At the bottom of this article I talk about colonies secondarily infected with EFB. This could also just be symptoms of EFB and PMS together.
EFB is normally transmitted when the bacterium becomes mixed with the bee bread, nectar or diluted honey, and then fed to young larvae. The bacteria then replicate in the larvae mid-gut, killing the larvae within 4-5 days from when the egg hatches. With “normal” EFB, beekeepers generally see open brood infected with the bacteria, though you may see some dead larvae under perforated sealed brood. This is because when a larva is fed the bacteria, they can either live or die, depending on the bacteria concentration, and also the size of the food mass in the mid-gut. I believe that these bacteria can also gradually starve out a larva, causing death in the pupa stage. There are many images below of different stages of EFB and two compound microscope pictures from I. B. Smith, Jr. at the USDA in Beltsville, MD.
Melissococcus plutonius from comb Photo Credit:USDA I. B. Smith, JrMelissococcus plutonius from comb Photo Credit: I. B. Smith, Jr.,USDAHere is the Brood Pattern from a colony with EFB. A brood pattern like this is a very good indicator that EFB was present within the past few weeks. Hygienic bees will remove sick larvae very fast making it hard to diagnose EFB or detect what is wrong with the hive.Brood frame with EFB and poor pattern.Healthy and EFB contaminated royal jelly.EFB Contaminated royal jelly.European Foulbrood contaminated brood food.Here you can see the larvae with EFB contaminated brood food in the cells.Close up of bacteria contaminated brood food.EFB contaminated royal jelly in larvae to the right of the queen cell.Egg laid in a cell with EFB Scale at the bottom. This would indicate the queen could tranfer the bacteria.Early stages of EFB in a few cells.Early Stages of EFB.Here you see early stages of EFB on the left and older stages on the right side. Some are close to becoming a scale in the cell.In this image you can see early to later stages of EFB, there is also some scale present. Note the new larvae look healthy and the brood food is not brown or yellow. This colony was treated with terramycin once.Different stages of EFB.EFB varies depending on secondary bacteria that move in once the larvae is comprimized.Here are larvae with the early stages of EFB, you can see one larvae starting to contort in the cell, commonly referred to as the “stomach ache position.”Here is some scale starting to form and also another larvae in the “stomach ache position.”This images shows most of the stages of EFB, however it does not show all the different types of secondary bacteria that can change its appearance and odor. Note that EFB does not always have an odor.Various stages of EFB with seconary bacteria.Another look at EFB, this symptom is most likely releated to one of the secondary bacteria that moves in.Here is brood in a colony with EFB, this is most likely result of a secondary bacteria.Another shot of what looks like a secondary bacteria infecting the larvae.European Foulbrood Infected brood.Larave in the “stomach ache position,” it also looks like this larvae has been infected by a secondary bacteria.Here are different stages of EFB, there is most likely a secondary bacteria involved here.EFB with secondary bacteria present.EFB larvae infected with secondary bacteria.EFB with secondary bacteria.EFB with secondary bacteria.Late stage of EFB with secondary bacteria.European foulbrood in late stages, lots of scale in the bottom of the cells.,European foulbrood in late stages, you can see the bees have cleaned up a lot of the infected larvae.Various stages of EFB.Larvae with sunken trachea visible.
Now I will discuss what I think is happening with a secondary infection due to mites. Mites can transfer EFB in a few ways, the first being when they enter the royal jelly before the cell is sealed. If the mite had the bacteria on its body, it could transfer bacteria to the brood food in the cell. The second method of EFB transfer is if the mite contained the bacteria inside the body, it could spread EFB through feeding. In this case, the mite would have to feed on the larvae once it’s free from the royal jelly. This would mean the larvae, now between 7½ and 8 ½ days old, has been infected with the bacteria. Normally larvae are infected as soon as they start consuming contaminated brood food. This infection with the bacteria at this late a stage in the life cycle may be detrimental to its lifespan and health because the limited food mass left in the bee. These symptoms are likely what are happening when you see signs of EFB in the open brood, and a lot of perforations in the sealed brood with different staged larvae/pupa. While the symptoms could look like mite damage, you clearly can see EFB infected larvae under perforated sealed brood (refer to images below). I have included images of what I believe is a colony secondarily infected with EFB by varroa mite. I also think these symptoms may be a delayed response to EFB or secondary bacteria. I have also included some EFB images above for reference. For more information on EFB see EFB Blog.
In this image you see the later signs of EFB where larvae are contorted then you also see lots of perforations in the sealed brood. The holes in the sealed brood are probably from workers uncapping mite infested cells.In this image you can see I circled a number of perforated cells. Some of these appear to have mite damage (uncapping) but the pupa could have also been secondarily infected by the EFB bacteria which killed them. The melted pupa in the perforated cells either has EFB/Secondary bacteria or they have just been cannibalized down by hygienic bees.In this image there is a lot going on. You see many sick larvae and also sick larvae under perforated sealed brood. There is also a larva in a cell with contaminated brood food. I would think mites have transferred EFB to the pupa under the capped cell or there was a delayed response to the bacteria causing it to die later.EFB with secondary bacteria and perforations in sealed brood.
If you see this contagious brood disease in your colonies, the recommended treatment is three dustings of terramycin, 5 to 7 days apart. If you want to be sure you have EFB you can use a cotton swab and a ziplock bag and send samples to the USDA to be tested. If the symptoms return, repeat the steps above to clear up the bacteria. Tylosin is another broad spectrum antibiotic used to treat gram positive organisms, EFB is a gram positive bacteria but I have heard rumors from beekeepers that this antibiotic does treat EFB.
