Bees/ov Development Journal 91
CONTROLLING AMERICAN FOULBROOD WITHOUT ANTIBIOTICS Cliff Van Eaton, Apiculture Consultant, Tauranga, New Zealand Keywords: antibiotic residues, honey, disease control, hive quarantine, New Zealand, Paenibacillus larvae In most parts of the world, antibiotics have been the recommended treatment for the control of American foulbrood for at least the last half
century. They have been accepted readily by many beekeepers, probably because antibiotics have been seen as a quick and easy
,
solution to one of the most economically significant bee diseases.
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The problem Administering antibiotics to bees is the same as giving them to other animals. If they are prescribed by a professional who first makes a competent diagnosis, and then applied according to label recommendation, symptoms of the disease are likely to be significantly reduced, if not altogether ‘cured’. If, however, they are administered routinely, and especially at a dose that does not kill all the diseasecausing bacteria, eventually a strain of the bacteria will develop that is resistant to the antibiotic (we have seen this many times with diseases in humans). During the late 1990s a strain was detected of the bacteria that causes American foulbrood
(AFB), Paenibacillus larvae subsp
larvae (PL) that was resistant to oxytetracycline. At the same time, food safety scares in Europe, together with increased sophistication in analytical equipment, meant that government health authorities in Europe and the USA began to take increased interest in
Diseased brood is discoloured and sunken. wifi a distinctive smell
At this stage, the bacteria produce spores, and the vegetative stage dies. The new spores are picked up by nurse bees when they attempt to clean up the remains of the dead larva. Thus the spores are spread around the hive during the constant exchange of food between all the adult bees in the hive. The cycle is finally complete when a nurse bee transfers the spores to another healthy young larva during feeding.
chemical residues in bee products. Beekeepers heard about the problems China experienced with Chloramphenicol in honey (see BfDJ 63), and now, honey and other bee products destined for human consumption are tested routinely for antibiotic residues.
PL spores are like tiny seeds. They have a very strong outer coat, and may remain viable hatch out into growing bacteria again for many years. However, they cannot hatch out again until they find their way back into the stomach of another young honey bee larva, because this is the only place in nature where PL can live. As it turns out, there must
Alternative treatment
be many spores in food that is always being transferred around the colony, and this food needs to be fed to a larva by a nurse bee, before
We now realise that using antibiotics to control AFB has become — problematic. The big question remains for beekeepers how do control this disease that can be so dangerous to my honey bees without |
the use of drugs?
New Zealand (NZ), with a beekeeping industry that is overwhelmingly commercial, and which produces the world-famous manuka honey, has
always had a legal ban on the feeding of antibiotics to honey bees. However - just because something is illegal does not mean it does not happen. Yet, over the years, extensive government inspections of NZ bee hives, as well as routine tests of NZ honey, confirm that beekeepers in NZ have not used the various antibiotics available to control AFB. There are a number of reasons for this, including strict control of such drugs by dispensing veterinarians. But perhaps the most important reason is simply that NZ beekeepers developed management practices that kept the number of AFB hives at low levels, and they did not see any gocd reason to change something that worked.
Understand the life cycle The NZ control system is based on an understanding of what causes a honey bee colony to develop visual symptoms of AFB, and how the disease spreads from hive to hive. PL is a spore forming bacteria, and it is the spores that cause an infection. The spores find their way into their host (a young larva) in the food provided by nurse bees. Once the spores have been ingested, they hatch and produce the vegetative (or growing) stage of the bacteria. The vegetative stage lives in the stomach of the young honey bee larva, and feeds on the larva until the larva dies.
there is a good chance for one or more of the spores to hatch.
So here is an important point - spores of PL are not particularly infective, and they need to be in high concentrations (at least 50 million/L) before a larva will become infected. Also for the infection to occur, the spores have to be in something that has a likelihood of
coming into direct contact with nurse bees, and through them, the larvae themselves. If we can accept these two important facts about PL, we can start to think differently about our beekeeping management. This is what NZ beekeepers have done. Their AFB control method is to car out management practices that lower the levels of PL spores in their hives.
Hazard analyses What are the materials we use in beekeeping that have a high risk of carrying large concentrations of PL spores in a form that will likely end up in the stomachs of young larvae? It will be obvious that combs with brood, honey and pollen can contain lots of spores. They are therefore always considered to be a high risk. House-cleaning bees, because they clean up dead larvae, and (possibly AFB infected ones), can have high numbers of spores, and because bees continually transfer food between each other, all the adult bees in the hive are high risk. Also bees constantly lick the insides of the hive, so supers, lids and floorboards
could have lots of spores, and are therefore high risk. honey is removed from a hive that has AFB the honey itself may have lots of spores. If this honey is extracted and does not come into contact again with nurse bees, it is low risk. However, the ‘wet’ frames (frames If
