- Describe the three honey bee diseases in the United States for which antimicrobial drugs have been approved.
- Explain the role of antimicrobial use in honey bees in the potential development of antimicrobial resistance.
- Explain how the changes from either over-the-counter status of drugs to prescription (Guidance for Industry [GFI] #213) or Veterinary Feed Directive (VFD) status impacts the use of certain antimicrobials in honey bees.
- Name the three antimicrobials approved in honey bees for prescription use or under the VFD in the United States, and describe why they may or may not be recommended.
- Describe the components of antimicrobial stewardship in honey bee disease management.
- Honey Bees in the United States
- Select Honey Bee Disease
- The Veterinary Feed Directive Final Rule
- Antimicrobial Drug Stewardship in Honey Bees
Honey Bees in the United States
APIS NEARCTICA FOSSIL (ENGEL, 2009)
Honey bees were long thought to have first been introduced to the New World by European settlers in 1622, and were called the “white man’s fly” by Native Americans (Engel, 2009). However, it was recently discovered that honey bees were once native to this continent, at least during the Middle Miocene period (11 to 16 million years ago): a fossilized honey bee was found in Nevada and classified as Apis nearctica (Engel, 2009). This native species is long extinct, and today all honey bees in the United States are the western honey bee, or Apis mellifera.
From the time of the first introduction to the eastern United States in the 17th century, western honey bee colonies have expanded across all 50 states to over 2.6 million colonies in the USA (USDA NASS, 2017).
In addition to producing honey, honey bees pollinate much of the world’s food crops, such as almond trees, alfalfa, sunflowers, and many fruits and vegetables, and contribute an estimated $20 billion to US crop production alone (USDA Farm Service Agency, n.d.).
Last year Mr. Beaman, a retired sheep farmer, started keeping bees in three colonies on his hobby farm. On a beautiful early spring day, he noticed that one of the colonies had an abnormal smell and a patchy appearance to the brood comb, the comb that contains the brood (bee eggs, larvae, and pupae). His good friend Ms. Honeycutt used to be a beekeeper, so Mr. Beaman called her for advice. She recommended he call a beekeeping supply company to get some antimicrobials to treat his bees for possible foulbrood.
When Mr. Beaman called the supply store, they informed him that they could not dispense antimicrobials over the counter and gave him the name of a local veterinarian who could come out to examine his bees and determine if antimicrobials would be needed. Mr. Beaman was rather surprised that a veterinarian would treat his bees, but curious, he went ahead and scheduled an appointment with Dr. Willoughby the next day.
Typical honey bees
A TYPICAL HIVE, WITH ADULT BEES AND CAPPED HONEY (A), POLLEN IN THE CELLS (B), AND BROOD (C).
Although most veterinary schools do not include bee diseases in the curriculum, there are courses available for veterinarians to learn about beekeeping and bee health. Veterinarians who have developed expertise in bees can be found by consulting the Honey Bee Veterinary Consortium (HBVC). The HBVC is an association of professionals and students within veterinary medicine and animal science designed to educate veterinarians and beekeepers about the health needs of bees and disease management.
From her training on honey bees, Dr. Willoughby was familiar with the appearance of healthy colonies and colonies diseased with foulbrood. The left-hand photo illustrates a typical hive, with adult bees and capped honey in the upper left corner, pollen in the cells along the middle, and brood (old larvae and pupae) in the lower right. A close-up of uncapped larvae and eggs is visible in the photo on the right (photo credits: AVMA).
A CLOSE-UP OF UNCAPPED LARVAE (D) AND EGGS (E).
After examining Mr. Beaman’s colonies the next day, Dr. Willoughby agreed with him that the one colony had an abnormal odor and appearance to the brood comb. Although there are several diseases that may lead to an abnormal brood comb appearance or odor, Dr. Willoughby told Mr. Beaman that her top two concerns were American Foulbrood and European Foulbrood. Nosema is another honey bee disease against which Dr. Willoughby could prescribe antimicrobial drugs, though the signs in Mr. Beaman’s colony did not fit this diagnosis specifically.
Select Honey Bee Disease
American Foulbrood (AFB)
- Very serious disease caused by the spore-forming bacterium, Paenibacillus larvae
- Affects the pre-pupal and pupal stages of honey bee development
- Bacterial spores transmitted to larvae via contaminated mouthparts of nurse bees, germinate in the larval gut, then multiply and cause larval death
- Resultant odor described as something between decomposing bees and rancid meat
- The bacteria are only susceptible to antimicrobial drugs when in the vegetative, or growing, stage
- AFB spores:
Are not affected by antimicrobials
Can persist in the environment for up to 70 years
Are readily transmitted via contaminated equipment, tools, hands, and via robber bees from other colonies
European Foulbrood (EFB)
- Caused by Melissococcus plutonius, a non-spore-forming bacterium
- Infects bee larvae via contaminated brood food
- Clinical symptoms appear in older larval stages
- Secondary bacterial infections common
- Larval death dependent on the amount of food available
Larvae are more likely to survive if larval nutrition is adequate
- Infection may result in a sour milk odor in the colony
- Although this bacterium does not produce spores, beekeeping equipment contaminated with the bacteria can serve as a source of infection for other colonies in subsequent years
- Caused by two fungus-like organisms, Nosema apis and Nosema ceranae
- Unlike AFB and EFB, which are diseases of the brood, Nosema is a disease of adult bees
- Upon ingestion, the Nosema spores germinate in the mid-gut, multiply, and eventually produce more spores, over 50 million in a heavily infected worker bee
- N. apis causes damage to the intestinal tract that results in spore-infested diarrhea and can reduce the honey bee’s lifespan by up to 78 percent (Mussen, 2011)
- N. ceranae was more recently identified and its pathogenesis is less-well understood. However, based on the results of the US national honey bee disease survey, N. ceranae is much more common in the USA compared to N. apis (Traynor et al., 2016).
Even though she did not detect the characteristic rancid AFB odor in the colony, Dr. Willoughby decided to do an onsite test to determine if the colony was likely infected with Paenibacillus larvae, since AFB is such a serious disease. She performed the matchstick test, which involves stirring a toothpick or matchstick into the larvae and withdrawing the stick. If AFB is present, the decaying larvae will be sticky and ropy. As the matchstick is slowly withdrawn, the infected larvae will appear as a sticky, brown thread, usually longer than one inch.
MATCH STICK TEST
Diagnosis of AFB
AFB kills brood that has been capped over with wax, which results in the typical clinical symptoms of a spotty sealed brood pattern, sunken wax capping over sealed brood, and holes in the wax cappings. The dead larvae are brown in color and can dry out, forming hard scales in the comb that contain infectious spores. (Photo credit: Hawai'i Department of Agriculture Apiary Program)
This video demonstrates how AFB can be diagnosed through the Matchstick test and other visual characteristics.
A definitive diagnosis and antibiotic susceptibility testing of AFB is available through the USDA Beltsville Bee Research Laboratory. AFB may also be identified via field diagnostic test kits or visually.
Fortunately, the matchstick test was negative and AFB was unlikely. Had the test been positive, Dr. Willoughby would have remembered that AFB is a reportable disease in some states and would have contacted her State Apiarist or Apiary Inspector. Based on the negative test, however, Dr. Willoughby suspected Mr. Beaman’s colony was infected with EFB. Indeed, the brood comb contained misshapen, uncapped larvae, similar to the one in the photo below, and the colony seemed to have a sour odor to it.
Dr. Willoughby took the time to teach Mr. Beaman how to perform this simple test so he could understand how to identify future scenarios in which to engage a veterinarian. She also took the time to explain the rationale behind her suspected diagnoses, including the visual appearance of the colony and the foul odor. She explained the difference between the sour odor of Mr. Beaman’s colony and the rancid odor of a colony with AFB, understanding that educating beekeepers is an essential component of her job.
Diagnosis of EFB
EFB may be diagnosed visually by experienced beekeepers or veterinarians, and it has a different appearance than AFB: the larvae typically die before the cell is capped and initially look contorted and yellowish to brown in the cell. An attempt at matchstick test will result in a more watery larva that ropes out less than 1.5 cm in length. A number of field test kits are available, and the USDA Beltsville Bee Research Laboratory can provide a definitive diagnosis through microscopic identification.
EFB v. Other larvae-deforming diseases
HEALTHY LARVAE (PERFECTBEE.COM)
HONEY BEE HIVE WITH EFB (ROB SNYDER, BEEINFORMED.ORG)
HONEY BEE HIVE WITH CHALKBROOD (SCIENTIFICBEEKEEPING.COM)
NOSEMA SPORES IN BEE COLONY
Diagnosis of Nosema
The presence and average number of Nosema spores per bee in a colony is determined by microscopic examination of a paste containing a specific number of ground-up bees, as described in this Nosema Disease explainer. The photo at right illustrates a microscopic view of N. apis (arrows) and N. cerenae spores.
Dr. Willoughby told Mr. Beaman she suspected the colony was infected with EFB and recommended that a sample be submitted to the USDA laboratory for a definitive diagnosis. Mr. Beaman replied that his experienced beekeeper friend, Ms. Honeycutt, told him his bees needed antimicrobials. Dr. Willoughby informed Mr. Beaman that she was very cautious about using antimicrobials in honey bees, because their use could lead to antimicrobial resistance. She explained that antimicrobial drug stewardship can greatly reduce the need for antimicrobials.
Since these concepts were not in practice when he was sheep farming, Mr. Beaman asked Dr. Willoughby to explain further. She briefly described the recent changes to the regulation of certain antimicrobial drugs in veterinary medicine, including an increase in veterinary oversight which made these products available by prescription through a Veterinary Feed Directive. Since Mr. Beaman was very interested, Dr. Willoughby provided him with the handout below with more details.
The Veterinary Feed Directive Final Rule
Labeled by the Food and Drug Administration (FDA) as “a strategy to ensure the judicious use of medically important antimicrobials in food-producing animals,” the Veterinary Feed Directive (VFD) Final Rule (USDA VFD module) went into effect on October 1, 2015. In January 2017, several over-the-counter antimicrobials were converted to VFD status under the Guidance for Industry (GFI) #213. Honey bees are sometimes medicated with a drug that is classified as a medicated feed. Such use falls under the regulations of the VFD. As with other animals, there was concern over the development of resistance to antimicrobials considered medically important to human medicine resulting from over-the-counter use in honey bees. As detailed in the One Health module, genes encoding for antimicrobial resistance can spread across ecosystems, potentially negatively impacting multiple animal species, including humans.
ANTIBIOTICS IN SUGAR (DOW GARDENS)
Historically, U.S. beekeepers used antimicrobials to control EFB and AFB (Tian, 2012). Oxytetracycline use began in the 1950s, followed more recently by lincomycin and tylosin, and these were all available over-the-counter until January 2017. At that time, antimicrobials were converted to prescription status (for the water soluble powders) and to VFD status for the medicated feed (oxytetracycline in some forms). Studies have demonstrated widespread resistance to oxytetracycline in the honey bee gut microbiota in the U.S., and little resistance in countries where such use has been prohibited (Tian, 2012).
After the implementation of GFI #213, these antimicrobials may now only be used under veterinary oversight, once a valid Veterinary-Client-Patient Relationship (VCPR) has been established. All three antimicrobials are labeled for the control and/or treatment of AFB, depending on the drug and formulation, but some strains are resistant to oxytetracycline. Oxytetracycline is the only one labeled for EFB control. Further classification of use of oxytetracycline, lincomycin, and tylosin is listed in Table 1 or can be found under the FDA’s FAQ about medically important antimicrobials in honey bees.
Fumagillin, the antibiotic used to treat Nosema, is not officially approved for use in the USA. The new regulations described above do not apply for this antibiotic, so its regulatory status remains unchanged.
VFD vs. prescription
Under the VFD Final Rule, antimicrobial drugs that are mixed with feed require a VFD Order from a licensed veterinarian. A traditional prescription must be written for antimicrobials that are sold in the water-soluble form, although these are not necessarily mixed with water for honey bee use. Table 1 below compares antimicrobial dispensing in honey bees for VFD drugs and prescription drugs.
|FDA-labeled drugs||Oxytetracycline only|
|How dispensed||Mixed in dry powdered sugar, sugar syrup, or patties*||Mixed into dry powdered sugar or sugar syrup|
Possible latitude under Compliance Policy Guide 615.115***
|Expiration||≤ 6 months|
** Extra label drug use
Extra-label drug use
Commercial beekeepers have traditionally used antimicrobials for the prevention and control of AFB and EFB. Preventive use is considered extra-label drug use (ELDU), as the antimicrobials are only labeled for the control—and some for treatment as well—of these diseases. Since ELDU is only legally allowed under a prescription, it is recommended that antimicrobials for prevention be dispensed via prescription rather than a VFD in honey bees, if they must be prescribed for uses outside their labeling (see Antimicrobial Stewardship section below).
Animal Drugs @ FDA provides a current list of FDA-approved drugs for honey bees.
Mr. Beaman had heard of the problem of antimicrobial resistance in people and was very glad to hear that the problem is being addressed in honey bees as well as other animals. He wanted to learn more about antimicrobial drug stewardship and asked Dr. Willoughby to explain the concept to him.
Antimicrobial Drug Stewardship in Honey Bees
According to the American Veterinary Medical Association, antimicrobial stewardship “involves maintaining animal health and welfare by implementing a variety of preventive and management strategies to prevent common diseases; using an evidence-based approach in making decisions to use antimicrobial drugs; and then using antimicrobials judiciously, sparingly, and with continual evaluation of the outcomes of therapy, respecting the client’s available resources” (AVMA, 2018).
In honey bee management, a number of strategies allow veterinarians and beekeepers to optimize their use of antimicrobial drugs. These include keeping so-called hygienic bees, regularly replacing comb, and minimizing the use of antimicrobials in disease control.
Honey bees bred for hygienic behavior detect and remove diseased brood from the hive before the disease reaches the infectious stage. The behavior of these hygienic bees provides a natural defense against AFB, a fungal disease called chalkbrood, and Varroa mites. Hygienic bees detect brood infected with these diseases or infested with Varroa and remove them from the colony. However, for reasons yet unknown, they do not provide a defense against EFB. Keeping hygienic bees can thus reduce the need for antimicrobial drugs for certain diseases.
Old or used comb may contain Nosema, chalkbrood, or AFB spores, the latter of which can remain viable for several decades. It is recommended that all comb be replaced at least every three years and that beekeepers do not purchase used comb. Other reasons to cull comb include pollen-bound cells and cocoon debris that shrinks cell size.
Judicious use of antimicrobials
As mentioned above, antimicrobials are ineffective against the environmentally resistant spores of AFB, and thus spores can cause reinfection once antimicrobial treatment is discontinued. In addition, some strains of AFB are resistant to oxytetracycline. Consequently, the use of antimicrobials to treat AFB is strongly discouraged, and the following steps are recommended to manage the disease (Spivak, 2016):
All bees are shaken off of the infected comb into brand new, comb-free frames
- A new queen must be introduced. Any queen is suitable, but one bred for hygienic behavior is ideal. Without a queen, bees will die as they have no larvae to work with to make a new queen
- To destroy the spores, all frames, combs, honey, and brood from the infected colony are burned, as illustrated in the photo on the right (photo credit: Food and Environment Research Agency, UK)
- Many states require the immediate burning of affected hive(s)
- Urban beekeepers must check with their local jurisdiction about open fires in their backyards
- In some states, ethylene oxide chambers are used
- In some states, the presence of spores is not equivalent to the presence of disease. Apiarists may be able to distinguish between these two scenarios
It is important to note that the above recommendations are primarily aimed at small-scale beekeepers, and US commercial beekeepers often choose to use antibiotics to prevent or control AFB in their colonies. A study of honey bee colonies in Connecticut from 2009 to 2012 demonstrated that almost half of the registered apiaries had AFB in at least one of their hives, illustrating the threat of this serious disease to the honey bee industry (Connecticut Agricultural Experiment Station, 2012). Given the number of commercial bee colonies in the USA, as mentioned above, this represents a potential significant input of antibiotics into the ecosystem, which must be weighed against the health and well-being of the honey bee industry.
It is also important to note that each state may have state-specific disease reporting requirements. Some states or jurisdictions may not allow hive burning. Always check with your State Apiarist or Apiary Inspector for the most current information.
Since brood survival depends on good nutrition, providing supplemental sugar syrup in early spring can increase larval resistance to EFB and result in resolution of the infection. Treatment with antimicrobials is recommended only as a last resort (Spivak, 2016).
Fumagillin, an antimicrobial first isolated from Aspergillus fumigatus, was used to treat Nosema disease for many years. Since it is not considered medically important, Fumagillin was available over-the-counter. Since the company making the US-approved product ceased operation, FDA allowed Fumagillin to be imported from Canada, despite it not being formally approved in the United States. However, the company in Canada has now ceased selling Fumagillin due to the lack of a supplier of the active pharmaceutical ingredient. Some leading bee disease experts advised against the use of Fumagillin anyway, as it can exacerbate the disease, especially if not used properly (Spivak, 2016).
As they concluded their discussion, Dr. Willoughby advised Mr. Beaman that she would be in touch as soon as she had the results from the USDA laboratory. In the meantime, in case the diagnosis was in fact EFB, she advised him to give his colonies supplemental sugar syrup to help the larvae resist the infection. She recommended he contact his local beekeeping association if he had questions about providing the supplemental feedings. Mr. Beaman thanked Dr. Willoughby for all the helpful information and planned to pass it on to his friend, Ms. Honeycutt.
- Bacterial honey bee brood diseases of concern include American Foulbrood (AFB) and European Foulbrood (EFB).
- Nosema is a microsporidian, or fungus-like, disease affecting adult bees.
- AFB is a reportable disease in some states and is diagnosed with a matchstick test, diagnostic field test kits, and antibiotic susceptibility testing.
- Commercial beekeepers have traditionally used antimicrobials mixed with feed for the prevention and control of AFB and EFB.
- Antimicrobials are ineffective against the environmentally-resistant spores of AFB.
- Under the VFD Final Rule, antimicrobial drugs that are mixed with feed require a VFD Order from a licensed veterinarian.
- Alternatives to antimicrobial use in honey bees include breeding for hygienic behavior, comb replacement, and supplemental nutrition.
United States Food & Drug Administration: Using Medically Important Antimicrobials in Bees - Questions and Answers
United States Food & Drug Administration: Medically Important Antimicrobials in Agriculture - Honey Bees
- Connecticut Agricultural Experiment Station. 2012. American foulbrood in honey bees: prevalence and geographic distribution of Paenibacillus larvae in Connecticut. United States Department of Agriculture, Research, Education & Economics Information System. Accessed Online March 2018.
- Engel, MS, I Hinojosa, and AP Rasnitsyn. 2009. A honey bee from the Miocene of Nevada and the biogeography of Apis (Hymenoptera: Apidae; Apini). Proceedings of the California Academy of Sciences, Series 4. 60:3:23-28.
- Food and Drug Administration (2013). Guidance for Industry #213. New Animal Drugs and New Animal Drug Combination Products Administered in or on Medicated Feed or Drinking Water of FoodProducing Animals: Recommendations for Drug Sponsors for Voluntarily Aligning Product Use Conditions with GFI #209. Accessed Online September 2018.
- Forsgren, E. (2010). European foulbrood in honey bees. Journal of Invertebrate Pathology, 103. doi:10.1016/j.jip.2009.06.016
- Genersch, E. (2010). American Foulbrood in honeybees and its causative agent, Paenibacillus larvae. Journal of Invertebrate Pathology, 103. doi:10.1016/j.jip.2009.06.015
- Mussen, EC. 2011. Diagnosing and Treating Nosema Disease. UC Davis Department of Entomology and Nematology. Accessed Online February 2018.
- Spivak, M and GS Reuter. 2016. Honey bee diseases and pests. A companion to Beekeeping in northern climates. University of Minnesota Extension, St. Paul, Minnesota.
- Tian, B, NH Fadhil, JE Powell, WK Kwong, and NA Moran. 2012. Long-term exposure to antibiotics has caused accumulation of resistance determinants in the gut microbiota of honeybees. Mbio. 3:6:e00377-12.
- Traynor, KS, K Rennich, E Forsgren, R Rose, J Pettis, G Kunkel, S Madella, J Evans, D Lopez, and D vanEngelsdorp. 2016. Multiyear survey targeting disease incidence in US honey bees. Apidologie, 47:3, pp.325-347.
- United States Department of Agriculture, National Agricultural Statistics Services. 2017. Honey Bee Colonies. Accessed Online February 2018.
- USDA Farm Service Agency. (n.d.). Pollinators. Retrieved from https://www.fsa.usda.gov/programs-and-services/economic-and-policy-analysis/natural-resources-analysis/pollinators/index