Oxytetracycline hydrochloride for the control of European foulbrood in honey bees
Source: Dr George Downing, Principal Veterinary Officer, Agriculture Victoria - Plant Biosecurity and Product Integrity (retired 2016) and Russell Goodman, Senior Apicultural Officer, Agriculture Victoria (retired 2016).
Reviewed and updated 2017: by Daniel Martin, Leading Apiary Officer - Agriculture Victoria.
European foulbrood (EFB) is a disease of honey bee brood caused by the bacterium Melissococcus plutonius. Diseased honey bee colonies may become weak and are unsuitable for honey production and the pollination of crops.
M. plutonius may be present in sub-clinical colonies in hives that show no signs of EFB. It is probable that most, if not all, honey bee colonies in Victoria carry latent infection.
It is generally accepted that the impact of EFB on Victorian beekeeping is greater than in any other Australian State (Hornitzky et al. 1996).
EFB usually first appears in hives in Victoria in early to mid-spring. Development of the disease can be very rapid. It may take only several days after the first symptoms are seen for a large proportion of larvae to be infected. Most diseased larvae fail to develop into adult bees and this causes rapid downsizing of the colony. Not all infected colonies die. Usually there is little or no warning of an impending outbreak, and even good operators can find the disease is in an advanced state requiring immediate treatment. This scenario is often exacerbated by the fact that hives may be hundreds of kilometres from the enterprise's home base and inspections of brood at such locations may be at weekly or even greater intervals.
The slow natural recovery from EFB causes colonies to be unproductive for an extended period, resulting in economic loss for the enterprise. Natural recovery is assisted by the occurrence of warm weather and improved conditions for bee foraging in late spring and early summer. Some beekeepers prefer to relocate diseased hives to an area sheltered from prevailing winds and with a good source of pollen. While this may assist with a more rapid recovery, it may not remove the need to treat infected colonies to restore them to productivity in the quickest time possible.
Oxytetracycline hydrochloride (OTC) and approved products
This antibiotic is a prescription animal remedy (PAR) and the only treatment approved by the Australian Pesticides and Veterinary Medicines Authority for the control of EFB.
Only the following four products are currently registered for the treatment of EFB (Melissococcus plutonius) in honey bees:
- Broodmix - Tetracin 10 soluble powder
- CCD OTC 100 soluble powder
- Tetravet 100 soluble antibiotic powder.
Broodmix and Tetracin 10 don't require mixing with a carrier and are applied directly to the hive in accordance with label directions. Some beekeepers have difficulty in calculating and precisely weighing the amount of product and carrier in the proportions stipulated on the product label. The use of premixed products will help prevent potential over- or under-treatment of hives. OTC is applied in powder form to the brood nest of hives. Application of OTC in sugar syrup was practiced in the past, but OTC products currently registered for the control of EFB have the following label statement: DO NOT USE as a wet treatment of bees. This is because wet treatment can cause residues in honey that exceed the current maximum residue limit (MRL). Food Safety Australia New Zealand has set an MRL of 0.3 ppm of OTC in honey. The Australian Honey Bee Industry Council's Pesticides and Prevention of Residues Sub-committee is surveying commercially produced honey for OTC residues to determine if this MRL may be reduced to reflect current use patterns.
Dr Bill Bailey, author of Honey Bee Pathology and EFB expert, advocated treatment of hives with OTC as early in the season as possible, before the time EFB symptoms were usually seen. This prevented multiplication and accumulation of M. plutonius and decreased the severity of outbreaks in spring or entirely prevented them (Bailey & Ball, 1991). An Agriculture Victoria (formerly Department of Primary Industries) survey of beekeepers in 1999, found 38 per cent of respondents followed Bailey's recommendation and treated all hives in an apiary (known as blanket treatment) around July every year.
OTC Use by beekeepers
Beekeepers should first contact an Agriculture Victoria Apiary Officer (contact details listed below) for a full copy of the OTC supply and treatment protocols for beekeepers.
Requirement for supply of OTC for control of EFB OTC may be required for:
- early season blanket treatment of colonies before disease symptoms are evident (e.g. around July prior to almond pollination in north-west Victoria)
- blanket treatment of colonies during spring when symptoms are evident and the bees are not on a honey flow
- spot treatments of hives expressing symptoms during spring and at other times during the beekeeping season (generally late winter, autumn).
EFB may reoccur in the odd hive after treatment and these hives are given a spot treatment whenever EFB is detected. This means that beekeepers with apiaries in locations around Victoria and interstate (often distant from their consulting veterinarian) will require OTC on hand for the immediate treatment of hives to control EFB throughout the beekeeping season.
Confirming presence or absence of EFB in an apiary
EFB can be confirmed by one of the following: ·
- Laboratory report confirming EFB from a recently submitted bee larval smear. Beekeepers have reported that it can take over three weeks to receive a report. This is enough time for the disease to economically affect bee colonies and production.
- Certificate of Confirmation from an Agriculture Victoria Apiary Officer who has confirmed clinical symptoms of EFB in bee larvae in cells of a brood comb.
- Inspection by a veterinarian of EFB infested brood comb and comparison with printed images in the Agriculture Victoria Information Note. A guide to the field diagnosis of honey bee brood diseases (Note Number AG0990).
Dispensing OTC to beekeepers
Veterinarians should first contact an Agriculture Victoria Apiary Officer (contact details listed below) for a full copy of the OTC supply and treatment protocols for veterinarians.
Understanding the beekeeper's enterprise
The veterinary practitioner will require a full understanding of the number of apiaries, the number of hives in each apiary and the beekeeper's brood disease management practices. This provides them with the basic knowledge and records for subsequent dispensing. Beekeepers must supply their current certificate of registration as a beekeeper which details the number of hives, and advise the veterinary practitioner of the number of apiaries/yards/loads. Failure to provide a current certificate of registration will mean that the veterinary practitioner may not dispense OTC. Beekeepers in Victoria must be registered with Agriculture Victoria in accordance with the Livestock Disease Control Act 1994.
Dispensing OTC and EFB
In general, confirmation that EFB is present in a beekeeper's apiary will be required to justify the dispensing of OTC. However at his/her first visit, there may be no disease present or records of disease from the previous season and the beekeeper may need a blanket treatment or spot treatment depending on how the beekeeper manages his/her hives. Provided that the information in 3.1 has been supplied by the beekeeper and he/she has agreed to record all details of use, dispensing of OTC should be acceptable.
After blanket treatments it can sometimes take several months before hives are affected with EFB again. At that time the beekeeper must collect appropriate material for diagnosis if additional OTC is to be dispensed.
If confirmation is not available, OTC may be dispensed for all hives in an apiary for an early season blanket treatment and enough to treat a few hives should there be a reoccurrence some months later. At the time the disease recurs, samples must be collected and submitted for diagnosis prior to further dispensing of OTC. If the requirement for blanket treatment is later in the season (spring) following an outbreak of EFB, then a sample must be provided by the beekeeper at that time. OTC can be dispensed once the sample has been received, with subsequent confirmation and advice to the beekeeper. The same procedure applies for spot treatments.
The presence of EFB in one hive can be taken as presumptive evidence that M. plutonius is present in all, or the majority, of hives within the apiary. Accordingly, OTC may be dispensed for immediate treatment of all the colonies and ongoing spot treatment if EFB is detected during that season.
Additionally, if there is no management of hives to avoid cross contamination between apiaries, it is likely that M. plutonius will be present in all the apiaries. The beekeeper may request sufficient OTC to treat all apiaries. The degree of evidence to be supplied by the beekeeper to justify supply of OTC for the entire enterprise will be determined by the veterinarian in consultation with the beekeeper.
Treatment of hives on more than one occasion during the beekeeping year may result from environmental conditions (weather, nectar and pollen availability) and poor management of hives. It could also be due to American foulbrood (Paenibacillus larvae) which is a notifiable disease, as well as other brood diseases and abnormalities. Reasons for breakdowns should be investigated before the continued dispensing of OTC.
OTC record requirements
Beekeepers must keep records of all OTC used, including dates, quantity, number of hives and which apiary is treated, as required by Agriculture Victoria. A copy of these records should be provided to the veterinarian for his/her records to support the quantity dispensed and used, and the basis of ongoing requirements for OTC.
American foulbrood disease (AFB)
AFB is another endemic honey bee brood disease that invariably kills infected bee colonies. It is caused by the bacterium Paenibacillus larvae which forms spores that remain viable for around 50 years and probably much longer. The spores are found in honey and on the components of infected hives, as well as dead infected bee larvae and pupae. Notification of an AFB outbreak is required by the Livestock Disease Control Act 1994. Infected colonies, bees and beeswax combs must be destroyed by burning, but hive components may be destroyed or sterilised by approved methods to render the spores non-viable. EFB and AFB may occur simultaneously in brood in the one hive, but never in a single larva. The application of OTC for the control of EFB also has an effect on AFB by inhibiting the vegetative growth of P. larvae. After OTC application, the bees remove AFB infected individuals and the remaining brood shows no disease signs. However, the spores in the hive remain unaffected, ready to initiate disease when the effect of the antibiotic wears off, usually after several months.
There is anecdotal evidence that some beekeepers treat AFB infected hives with OTC. This treatment is contraindicated on all four OTC products registered for the control of EFB.
There is no mandatory requirement for beekeepers to provide evidence that their hives are free from AFB before OTC is supplied by a veterinarian for the control of EFB. Agriculture Victoria encourages beekeepers to regularly check their hives for clinical symptoms of AFB and to submit samples of honey for laboratory detection of P. larvae spores. These subjects are detailed in Information Notes on Agriculture Victoria's website.
- Bailey L & Ball BV (1991). Honey bee pathology (second edition). Academic Press Limited, London. Page 41-48.
- Downing G (2012). Oxytetracycline hydrochloride for control of European foulbrood of honey bees.
- Goodman R (2012). Oxytetracycline hydrochloride for control of European foulbrood of honey bees.
- Hornitzky M, McDonald R & Kleinschmidt G (1996). Commercial beekeeping in Victoria. A report produced by the Honeybee Research and Development Committee. Page 10.