American Foul Brood
Paenibacillus larvae
FLORIDA DEPARTMENT OF
AGRICULTURE AND CONSUMER SERVICE
Plant Industry
Bureau of Plant & Apiary Inspection
APIARY INSPECTION SECTION
American Foul Brood (AFB), caused by the spore- forming bacterium Paenibacillus
larvae subsp. larvae (formerly Bacillus larvae) is highly contagious, most widespread,
and destructive brood disease of the honeybees (Apis mellifera L.). Larvae of 3 days or
less become infected by ingesting spores that are present in their food. Spores germinate
in the gut of the larva and the vegetative form begins to grow, taking its nourishment
from the larva. Spores will not germinate in larvae over 3 days old. Bacterial growth
causes the eventual death of the larva or young pupae as the cells are being sealed. The
vegetative form of the bacterium will die but not before it produces many millions of
spores. Each dead larva may contain as many as 100 million spores.
Other brood ailments that are sometimes confused as AFB, are Paenibacillus species
and species of the genera Bacillus, Brevibacillus, and Virgibacillus were consistently
reported as being isolated from apiary material. The complex microbial community of
spore formers includes Paenibacillus alvei, Brevibacillus laterosporus, and Paenibacillus
apiarius, which are considered secondary bacterial invaders of larvae infected with
European foulbrood (EFB), P. larvae subsp. pulvifaciens; Powder scale and Bacillus
coagulans; half-moon disorder which cause diseases of minor economical impact.
Spread of Disease
Disease spreads rapidly throughout the hive as the bees attempting to remove the sporeladen dead larvae, contaminate brood food. Nectar stored in contaminated cells will
contain spores and soon the brood chamber becomes filled with contaminated honey. As
this honey is moved up into the supers, the entire hive becomes contaminated with
spores. When the colony becomes weak from AFB infection, robber bees may enter and
take contaminated honey back to their hives thereby spreading the disease to other
colonies and apiaries. Beekeepers also may spread disease by moving equipment (frames
or supers) from contaminated hives to healthy ones.
American Foul Brood spores are extremely resistant to dehydration and can remain viable
for more than 70 years in honey and beekeeping equipment. Therefore honey from an
unknown source should never be used as bee feed, and used beekeeping equipment
should be assumed contaminated.
Symptoms
Clinical signs

As the larval and pupae die they lay flat in the cells and the color changes to
creamy brown, then dark brown.

Capped cell containing diseased larvae appear moist and darkened, larva shrinks,
the capping is drawn into the mouth of the cell and becomes concave (sunken in).
Some of the cells caps will be pierced and have jagged holes chewed in them.

Dead larvae and pupae display a characteristic "roping" when a small probe
(match stick, tooth pick) is used to slightly stir the diseased tissue in the cell,
slowly pulling the probe out the dead tissue will string out approximately 3/4”.

Dead larvae and pupae produce an unpleasant odor.

Death in the pupa stage results in the formation of the pupa tongue, a protrusion
from the dried pupa head which is one of the most characteristic signs of the
disease.

Diseased brood eventually dries out to form characteristic brittle scales lying flat
on the bottom of the cell adhering tightly to the wall. The scales are virtually
impossible for bees to remove.
Identification
Concave Cell Caps
Roping Brood
Dried Scale
Pupas Tongue
Roping Test
If a stick is inserted and slowly withdrawn, the remains can be drawn out in a brown,
mucus-like thread ‘rope’ at least ¾ inch long. This is called the ‘roping’ test and is a
reliable test for the presence of AFB.
Dried Scales in comb
Holding the frame by the top bar in the sun light, looking from the top of the frame
downwards, the scales are noticeable on the bottom front edge of the cells. The dead
larva will be lying flat lengthwise in cells not curled. These scales adhering tightly to
the cell walls are very difficult for bees to remove. Dried tongues of the pupas are
visible in the open cells.
Comparative symptoms of various brood diseases of honey bees
European
Sacbrood
Chalk brood
Foulbrood
Unsealed brood.
Some sealed brood
Sealed brood.
Sealed brood.
in advanced cases
Scattered cells with Sealed and unsealed
Appearance of
Discolored, sunken, or with discolored,
punctured cappings.
brood.
brood comb
punctured cappings.
sunken or
often with two holes
punctured
cappings.
Usually young
Usually older sealed unsealed larvae;
Usually older sealed
occasionally older
Usually older larvae,
Age of dead
larvae or young
larvae. Length wise
pupae.* Lying
sealed larvae.
lengthwise in cells.
brood
in cells.
lengthwise in cells. Typically in coiled
stage.
Dull white,
Grayish or straw
Dull white, becoming
becoming
colored becoming
Chalk white.
light brown, coffee
Color of dead
yellowish white to
brown, grayish
Sometimes mottled
brown to dark brown,
brood
brown, dark brown, black, or black; head
with black spots
or almost black.
or almost black.
and end darker.
Watery; rarely
Watery and
Consistency of Soft, becoming sticky
sticky or ropy.
Pasty
granular; tough
dead brood
to ropy.
Granular.
skin forms a sac.
Slightly to
None to slightly
Yeast like, not
Odor of dead Slightly to pronounced
putrid odor.
penetrating sour.
sour.
objectionable
brood
Lies uniformly flat on
Head prominently
Mummified. Does
lower side of cell.
Usually twisted in curled towards center not adhere to cell
Adheres tightly to cell
cell. Does not
of cell. Does not walls. Brittle. Usually
Scale
wall. Fine, threadlike adhere to cell wall. adhere tightly to cell chalky white in color.
characteristics
tongue of dead maybe Rubbery. Black in wall. Rough texture.
Sometimes black
present. Head lies flat.
color.
Brittle. Black, in
fruiting bodies are
Black in color.
color.
present
*Bold text
From Diagnosis of Hachiro Shimanuki1
indicates the most
Honey Bee
and
useful field
Diseases
USDA
David A. Knox
characteristic
Symptom
American Foulbrood