The Bane of Bees-AFB

     Surely you've seen a little fellow like this buzzing around your yard or garden. If you're especially lucky, you'll see those beautiful pollen baskets on their legs stuffed full of orange or yellow pollen! This is a honeybee, responsible for over 90% of commercial pollination across open land (Fünfhaus et al., 2018). Think of that number for a moment...the Western honey bee (Apis mellifera) is responsible for over 90% of pollination that occurs on the open landscape. The sad thing is that honeybees are at risk, there have been reports on large-scale honey bee colony losses (Fünfhaus et al., 2018).

     One of the greatest risks currently presented to honey bee colonies is a bacterial infection called American Foulbrood (or AFB). This disease is a nasty little bacterium called Paenibacillus larvae, rightly named because it attacks the larvae of honey bees while they're still growing in their cells. It is considered to be the best studied and most destructive bacterial disease of honey bees. My main resource for this post comes from the article 'Diagnosing and Treating American Foulbrood in Honey Bee Colonies' from Michigan State University, you can find the reading here.

     Before we continue, let's break down that name "foulbrood." Just like how the scientific name is rightly named for its attack on the defenseless larvae of the honeybee, the name "foulbrood" perfectly describes the design of the disease in two ways. "Foul" because fo the foul odor that comes from the hives that are infected with AFB, and "brood" because the bacterium affects the brood of the hive.

   
Gram-negative vs. Gram-positive bacteria

     AFB is a gram-negative bacteria which sounds like a scary term when you read it, but using the picture above, all that really means is that they have an extra cell membrane that covers them while gram-positive bacteria do not. When trying to determine what type of bacteria one is working with, there is a violet dye that a slide can be dipped in, bacteria that do not retain this "crystal violet dye" are considered gram-negative. Clinical signs can be variable and case dependent, however there are 6 signs that generally prove to be characteristic of AFB:
1) Spotted brood pattern
2) Sunken cappings
3) Off-center holes in cappings
4) Larval scale
5) Caramel color of the dead larvae
6) Pupal tongue
     AFB's strategy for infection really is a nefarious art form in that it goes for the hives young larval bees. The spores are generally introduced early into the larval brood, at around 12-48 hours old and are carried in and around to other larvae by the nurse bees. These spores invade the larvae and make themselves at home in the intestines wehre they reproduce and colonize inside of the larvae. As the spores reproduce, they release toxins into the larval tissues that essentially liquify the larvae from the inside out. As this process continues, it inevitably leads to sepsis (the body's response to harmful organisms which can lead to malfunctioning of organs, shock, and death) and death. Once death occurs, a single larvae has the potential to contain upwards of millions of infectious spores. 

Normal hive (left) vs. AFB affected hive (right)
      According to MSU there are three particular reasons why AFB is so serious for bees:
1) AFB has a highly persistent spore form that can remain infectious for decades and spread easily to other colonies. 
2) AFB can devastate an otherwise healthy hive. It does not require another stressor, and colonies do not spontaneously recover--AFB generally leads to death. 
3) It is highly infectious--only a few spores are needed to cause infection in an otherwise healthy colony. 

     This is all so dark and dreary to think about, but this is one example of a potential light at the end of the tunnel, the light in this case is a vaccine against AFB. The vaccine is currently in the testing phase by researchers at the University of Helsinki in Finland. There is skepticism involved of course, as there always seems to be when a potential "cure" is introduced (for another example, see my CWD cure blog post). A vaccine for insects has long been considered a tough problem to solve because insects, while they do have an immune system, do not have antibodies to fight off infection. Basically they do not have an internal immune memory for fighting off diseases. Through this research, scientists have discovered that a protein called vitellogenin has the potential to help increase the immune response of both adult and larval bees.
   
     The University of Helsinki posted a news release stating, "When the queen bee eats something with pathogens in it, the pathogen signature molecules are bound by vitellogenin. Vitellogenin then carries these signature molecules into the queen's eggs, where they work as inducers for future immune responses." Until the vaccine is further tested and produced for hives across the country the D.C. Beekeepers Alliance in Washington D.C. recommends that beekeepers never purchase used beehives or other beekeeping equipment and in the event that "...if a colony is diagnosed with AFB--regardless fo the level of the infestation--it burns. Every bit of it burns; the bees are killed and the woodenware burns, and it's gone."

Literature Cited:
Chappell, B. (2018, December 7). World's first insect vaccine could help bees fight off deadly disease. Retrieved from National Public Radio: IwAR1kD4Kd_D31vhdhiJiEvLYHxf8Wx22QGlMwr3aP9kbORvmyWwfCiPFhN7s
Earth Rangers. (2014, April 16). 6 Reasons Bees are Your BFF. Retrieved from Earth Rangers: https://www.earthrangers.com/wildwire/take-action/6-reasons-bees-are-your-bff/
Fünfhaus, A., Ebeling, J., & Genersch, E. (2018). Bacterial pathogens of bees. Current Opinion in Insect Science, 26:89-96.
Milbrath, M. (2018). Diagnosing and treating American foulbrood in honey bee colonies. Retrieved from Michigan State University Michigan Pollinator Initiative: https://pollinators.msu.edu/resources/beekeepers/diagnosing-and-treating-american-foulbrood-in-honey-bee-colonies/
Sarich, C. (2013, August 15). List of Foods We Will Lose if We Don't Save the Bees. Retrieved from Honey Love Urban Beekeepers: https://honeylove.org/list-of-food/



















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