↑ Return to Ohio Fact Sheets

American Foulbrood- AFB

94-7     
BEEKEEPING INFORMATION
OHIO DEPARTMENT OF AGRICULTURE
Division of Plant Industry -Apiculture
995 East Main Street
Reynoldsburg, Ohio 43068-3399

AMERICAN FOULBROOD – AFB

 

Cause: It is caused by a spore forming bacteria known as Paenibacillus larvae. Only the spore stage is infectious to honey bees. All castes of honey bees are susceptible to the disease, but worker larvae are particularly susceptible. However, larvae become immune to the disease about 3 days after the egg hatches.

Effect: The strength of a recently infected colony will not be noticeably affected, and only one or a few dead larvae or pupae will be seen. Occasionally enough larvae become infected to weaken or kill the colony the first season. On the other hand, the disease may not develop to a critical stage until the following year.

Symptoms: Death occurs rather uniformly after the larvae have been capped over, have spun their cocoons, and are fully extended on the floor of the cell. Also death can occur after the pupa has formed but before the body is pigmented.

Soon after death the glistening white or formerly healthy larvae and pupae changes to dull white. About 2 weeks after death they become light brown and the well-rounded appearance is lost. The dead brood gradually sink in the cells during decay and become darker, changing from a light coffee brown to dark chocolate brown by the end of the fourth week. Scales are very dark brown or nearly black. The decay and drying of dead brood ordinarily require a month or more. Scales are difficult to distinguish in old brood comb, since they are about the same color as the comb, but in new comb they are easily identified.

During the early stages of decay, the body wall is easily ruptured and the tissues are soft and watery. Occasionally, the body divisions of the dead larvae are more clearly marked than are those in healthy ones. The consistency of dead brood becomes characteristically gluelike about 3 weeks after death. When a toothpick is thrust into a decayed larvae and withdrawn, the decaying mass adheres and can be drawn out an inch or more in a gluelike thread (rope test). Decayed larvae finally become dry, brittle scales.

These scales lie extended along the lower side wall, with their posterior end curved in the bottom of the cells. A small raised swelling may occur near the head of the scale, but it is rarely prominent. In advanced cases, rows of cells contain scales uniformly in this position.

Occasionally, cross markings, which represent the segmentation of the larvae, can be seen on the scales. When completely dried, the scale adheres to tightly to the cell walls that it is difficult to remove without breaking. When death occurs after pupation has started, the form of the pupa can be recognized. The mouth parts of the dead pupa may protrude from the head and appear as a fine thread slanting slightly backward into the cell and at times adhering to the upper wall.

In the first stages of decay, while the remains are still white, practically no odor is detectable. When the remains begin to turn brown and become ropy, an odor develops. In later stages, when the dead brood is brown and decidedly ropy, the odor is always present (gluepot odor); but it practically disappears when the scales are completely dry. In advanced cases, when much decaying brood is present, the odor can be detected even a foot or more from the combs.

Spread:
  1. Nurse bees transmit bacillus spores to young larvae.
  2. Honey stored in cells that once contained diseased larvae.
  3. Bees are exposed to contaminated honey.
  4. The same equipment is used for both diseased and healthy colonies.
Nurse bees can inadvertently feed bacillus spores to young larvae. Soon after the larva has been sealed in its cell or just after it changes to a pupa, the spores will germinate in the gut of the larva and multiply rapidly, causing death. New spores will form by the time the larva dies. When the house bees clean out the cell containing the dead larva, spores will be distributed throughout the hive, thus infecting more larvae.

Honey stored in cells that once contained diseased brood becomes contaminated and may be fed to susceptible larvae. As the infection weakens a colony, the colony cannot defend itself from robber bees from strong colonies. The robber bees take the contaminated honey to their own colony and repeat the cycle of infection and robbing.

When bees are exposed to contaminated honey, or the same equipment is used for diseased and healthy colonies, there can be a danger of disease spread. Therefore, it is extremely important that diseases are detected in their early stages, and that equipment is free from disease organisms.

Control: The beekeeper has the following control options:
  1. Feed antibiotics (Terramycin) per label.
  2. Destroy diseased colonies by burning.
  3. A combination, both 1 and 2.
Many times the degree of infection will determine your control option. Therefore, it is important to choose the correct control for best results.

 

Prepared by: Gordon Rudloff
State Apiarist
Ohio Department of Agriculture

Permanent link to this article: http://www.ohiostatebeekeepers.org/resources/ohio-fact-sheets/american-foulbrood-afb/

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>