American Foul Brood

 

Causal agent

Paenibacillus larvae

Slender rod with slightly rounded ends with a tendency to grow in chains. Produces spores. Does not grow on nutrient agar – requires Difco brain-heart infusion.

Other names

AFB

Age group

Larvae after capping – worker 12 days of age

Some strains may attack uncapped larvae

Egg

Larvae

Pupae

Adult - worker

Drone

Queen

No

Yes

 

 

 

 

Clinical signs

Season

Any time

Odour

There is a characteristic odour (decayed glue pot) to the brood when frames removed

Brood

Brood appears spotty

Cappings

Sealed brood. The cappings become discoloured and convex (sunk inwards). Some may be punctured.

Larvae appearance

Dead larvae may be sticky and ropey – use a tooth pick.  Their colour is dull white, becoming light brown to almost black.

Scales (larvae)

Dead dried larvae (called scales) are difficult to remove.  Fine threadlike tongue of dead pupae maybe present.

Spotty brood patter –“pepper pot:

Black shrunken caps and scales (dead larvae)

 

Scales visible in the cells

Torn cappings – in a collapsing hive


 

Infectivity

 

 

The larvae are infected within the 1st couple of days. 

The bacteria cannot affect hatched larvae older than 3 days of age.

The bacteria is spread between colonies by robbing

The bacteria gains access to the larvae trough infected honey

The bacteria produce spores which are extremely resistant and can survive 40 years. (Note paeni – next to in Greek)

 

Transmission

 

 

Through infected honey.  Spores are highly resistant and can remain viable for over 70 years.

 

Post-mortem Lesions

 

 

Dead larvae after 16 days of age (worker) post-capping

Larvae are not pure white – may range from translucent, tan to black.

 

Diagnosis

 

DSC01287

Culture of the organism

Field diagnosis using  lateral flow devices looking for antibodies in the bees

Rope test using a match stick on the dead larvae – shown left.

Note this is not diagnostic as most brown decomposing larvae may do this.

 

Treatment

 

 

Inform local authorities – several countries will destroy the hive

 

Tetracycline, Tylosin or Sulphathiazole

 

Note residue issues with honey

 

Control

Strict biosecurity – do not shape equipment,  Avoid second hand equipment

 

Burn equipment which has become infected

 

 

When applying antibiotic medications, mix the antibiotic with powdered sugar. Sprinkle the mixture on the edge of the brood-nest avoiding spilling directly into the brood.  The house bees will consume the medication and feed it to the larvae.

 

Common differentials

 

 

European Foul Brood – not larvae die before being capped.

 

Zoonosis

None