About Bacterial Diseases

There are two bacterial diseases that beekeepers must be on the lookout for they are American Foulbrood and European Foulbrood.

The American Foulbrood, also known as AFB, is the most serious of the bacterial diseases of honeybee brood and is caused by the bacterium Paenibacillus larvae.  This disease is started and can be transferred only in the spore stage.  The reason for the seriousness of the disease is the spores can remain alive and last for an undetermined length of time on beekeeper’s equipment.  It is highly contagious and spreads easily via contaminated equipment, hive tools, and beekeeper’s hands.  The best way to handle the American Foulbrood is to avoid it at all possibilities.

To detect the disease examine the larvae.  Normal healthy larvae are white, but the infected broods turn chocolate-brown and melt into a gooey mass on the floor of the cell.  The colonies will display a “pepper box symptom” as the disease progresses.  The “pepper box symptom” is when the bees are capping the cells, the brood capping are perforated and sunken into the cell.  When the larvae are brown and have not formed a hardened scale, the symptom of ropiness can be demonstrated.  To do this, poke at stick into this mass, moisten it and withdraw it from the cell.  The contents will draw out like melted cheese, the ropiness, if AFB is present.  As the dead larvae dries, it becomes a black scale that sticks tightly to the cell floor.  These scales are difficult to remove and are site for re-infection.  A single scale can contain one billion spores.  It only takes 35 spores to trigger the disease.  These scales are difficult to see and easily missed when purchasing used equipment.  If you are around a colony that is extremely infected with American Foulbrood, it will emit a foul odor like a chicken coop.  The colony dwindles and eventually collapses as more and more brood become infected and dies.  

The beekeeper has an advantage if new equipment and tools can be purchased, install packaged bees and maintain them in total isolation from other apiaries, hive collections.  Of course this is not realistic or practical, but it always makes good sense to practice sanitation, such as washing hands and hive tools regularly.  Avoid using hive equipment of unknown history, and avoid feeding bees honey from an unknown source.

It is possible to breed bees that are genetically resistant to American Foulbrood and other diseases.  One of the most important characteristics is the disease resistant bees is the ability to detect and remove from the colony abnormal cells of brood.  The resistant queens are available from nationally advertised queen breeders.  You will find the advertisements in the “American Bee Journal”, “Bee Culture”, and “Speedy Bee”.

European Foulbrood, also known as EFB, is another of the bacterial diseases that effect the honeybee brood.  There are some differences between the European Foulbrood and the American Foulbrood.  The colonies infected with the American Foulbrood sometimes recover from the infection.  The symptoms can sometimes be mistaken for those of the American Foulbrood, but there are some important differences.  Instead of being a normal healthy white, the larvae with European Foulbrood are off-white, progressing into a brown, and are twisted in various positions in the cell.  Larvae with European Foulbrood usually die before they are capped whereas with American Foulbrood die after they are capped.  

The sanitation precautions recommended in the section on American Foulbrood also apply to the European Foulbrood.  Bee stocks that are bred for resistance to diseases can be expected to minimize outbreaks of European Foulbrood.  There are times at the onset of a strong nectar flow that the disease will go away on its own.  The beekeeper may be able to control the disease by stimulating a nectar flow and by requeening the colony.

There is a preventative measure that can be used on either the American Foulbrood or the European Foulbrood, and is periodical treatments of the veterinary antibiotic TerramycinJ.  It is fed as a mixture in either powdered sugar, sugar syrup, or in vegetable oil extender patties.  It is very important to never feed the antibiotic within four weeks of a nectar flow to avoid contamination honey for human consumption.

The use of TerramycinJ in European Foulbrood infected colonies may actually be counter productive because the medication permits those infected larvae to survive when they would have died.  These survivors then are in the colony as a source of recontamination.  If the infected larvae die instead, the house bees eject them from the hive and with them the source of the infection.  The bacterium does not form long-surviving spores that will stay on the hive surfaces.

There has been recent evidence of the disease becoming resistant to the antibiotic.  One of the suspected causes is the use of the oil extender patties as a method of medicating the bees.  If the bees do not consume the patties rapidly, it leads to the antibiotic staying in the hive for weeks or even months.  Until the use of the oil extender patties in the 1990’s, resistance was not a problem.  Beekeepers are now being told to remove uneaten patties after a month.

Sacbrood is a virus infection that is like a cold in humans.  There is no known cure at this time.  The best preventive measure is sanitation.  Comb replacement and requeening the colony is the best response to the infection.

Beekeepers do not consider sacbrood a serious threat, however one larva killed by the sacbrood virus contains enough virus to kill over one million larvae.  More research needs to be done on the sacbrood virus.  It is unknown how the virus is transmitted to the larvae in nature, why severe outbreaks occur only during build-up season, or how the virus seems to return year after year.

Symptoms of sacbrood are partially uncapped cells scattered about the frame or capped cells that remain sealed after others have emerged.  Diseased bees inside the cells will have darkened heads, which curl upward.  The dead prepupa resembles a slipper inside the cell.  Diseased prepupae fail to pupate and turn from pearl white to pale yellow to light brown and finally, dark brown.  The skin is loose and flabby and the body watery.  The dark brown bee becomes a wrinkled, brittle scale that is easily removed from the cells.

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