3.1 - 3.5 - AFB Flashcards
AFB Cause
(A Pain in the back love) Remember pAenibacullus for AFB
Caused by spore forming bacterium: PAenibacillus Larvae. Infected bees die from septicemia.
1 Young bees become infected when they consume the larvae in their food
2 Spores germinate in the gut
3 Bacteria moves into gut tissues where they multiply
4 Infected larvae normally die after the cell is sealed
5 Millions of infected spores are formed in their remains which dry to form scales that adhere closely to the cell walls and cannot easily be removed by bees
6 Consequently brood combs from infected colonies are severely contaminated with bacterial spores
If the combs are used or moved between colonies infection can spread quickly
7 The spores are very resistant to disinfectant and extreme heat or cold. They retain their powers of germination for many years in honey, in old combs
8 Once a colony is infected the disease spreads until most of the brood is infected.
9 The colony becomes unable to replacing aging bee population causing it to become weakened and die out
10 The disease can develop for months before the colony succumbs
11 Death can occur at any time of the year
Describe the impact of AFB in colony 9
- Nurse bees pick up the spores and infect larvae through brood food.
- larva under 24-hours larva req ten of spores to die
- 3-day larva req millions of spores to die
- Pupae die of scepticemia
- Impact is loss of brood; colony may recover from <100 infected larvae, not if >100
- Slow to build up, but once enough cells are infected, pupae die faster than queen can lay new eggs, so colony dies out.
- Queen won’t lay in cells with scales - so pepperpot exacerbated
- Weakened colonies target for robbers, so spreads disease.
- Spores in black scale, > house bees try to remove, and become infected
- Spores survive up to 50+ years (Gregory 31) heat /disinfectant/ desiccation and get everywhere inc honey.
AFB Control
Notifiable disease (under Bee Diseases and Pests Control Orders (for England and Wales))
Subject to official control programme of apiary inspections carried out by NBU
Control of disease is by compulsory destruction of infected colonies (highly effective since 1940’s bringing incidence of AFB down from several thousand infected colonies per year to less than 100)
Antibiotics are used in some countries but only suppress signs of the disease without eradicating it and allow the development of resistant bacterial strains.
AFB Diagnosis
A suspect sample is tested using a LFD field kit.
Sometimes combs or infected larvae are sent to the `NBU where they are examined for the presence of causative bacteria.
Infected colonies are destroyed by burning under supervision of a bee inspector
The bees are killed and they, together with the combs are safely burned in a deep pit
Hives and appliances can be sterilised by thoroughly scorching them with a blow lamp.
Gloves, overalls, footwear and the smoker are washed in washing soda or hot soapy water
AFB Lifecycle and causative effects
The disease attacks only the very young larvae; larvae older than 48 hours and adult bees are not susceptible to it.
AFB is caused by the spore-forming bacterium known as Paenibacillus larvae. The bacterium exists in two forms: the spore stage and the vegetative stage, which consists of slender rod-shaped bacterial cells. Only the spore stage is contagious to bees.
Pathogenesis:
Bee larvae become infected when they ingest Paenibacillus Larvae spores in brood food given to them by nurse bees. A day after ingestion the spores germinate in the larval mid-gut into the vegetative form (rod stage), becoming bacteria. The rods penetrate the gut wall, entering the tissues where they proliferate rapidly and at an enormous rate, feeding at the expense of the tissues, until the larva dies. The larva dies after its cell has been sealed; sealing the cell stops the supply of nourishment to the bacteria; they cease to grow and proliferate, and revert to the spore stage.
After death, the normally white larvae turn dark brown and decay into a glue-like mass, which will form a rope. The decaying mass has a foul smell - hence the name, foulbrood.
At the final stage, within a month or so, a dead larva or pupa dries to a dark brown scale that adheres tightly to the lower side of the cell too tightly for the bees to remove. Each scale contains millions of infective spores. Once they are inside the larval gut again, the cycle repeats itself.
A detailed account of development within the colony
Infection of the larva is by ingestion of the spores in contaminated brood food.
The conditions in the larval gut are ideal for germination and the bacterial population doubles about every 8 hours.
Sporulation begins when the larva voids the contents of its gut before metamorphosis, and the cell contents become a source of further infection.
Bacteria continue to multiply in the haemolymph and eventually cause the larva to die.
Once the larva dies the bacteria again sporulate within its body. Adult bees become infected as they clean away the dead remains in the hive.
AFB bacteria gradually destroy larval tissue.
House-cleaning bees come along and try clean up both the messy (pre)pupae and the scales, so becoming contaminated with the spores. The spores can get into every part of the hive including the honey. House- cleaning bees soon become nurse bees, feeding young larvae, and the spores will be passed to the larvae in this way. The disease may be quite slow to get going in the beginning; the bees can keep the spread under control for a time by the removal of diseased larvae in early stages. As the number of young bees declines the disease takes control and quickly destroys the colony.
What are the signs of AFB? 6
- Uneven brood pattern - pepperpot - queen won’t lay in cells with scales
- Perforated cappings - sunken, raggedy holes on edge of capping
- Pupae turning yellow to brown, proboscis out
- Match stick rope 10-30mm”
- Larvae dry up to dark brown scale at the bottom of the cells
- Tongue like proboscis remains intact and may protrude upwards.
- • Final stage - rough dark scale on lower side of cell, lying from front to back and reflecting light.
- Scales won’t come out.
Describe the lifecycle of AFB 7
- Life cycle 10-15 days (Yate 187)
-
Spores ingested in larval food
- Larvae up to 24 hrs succumb with just 10 spores
- Larvae 3+ days need millions
- Germinate in gut producing vegetative cells (do not multiply)
- Upon sealing, vegetative cells penetrate gut wall into haemolymph, where they multiply (Yates 188)
- Sporulation (dormant form) enables bacteria to survive harsh conditions until ingested. Infective 35+ years and resistant to heat, desiccation and disinfectant
- Death by septicaemia. Pupa melts, thickens and dries to a scale with proboscis protruding from scale to cell centre, a mass of bacterial spores
- As HB try to clean the cell for more eggs, they recycle toe spores around the colony. When they become nurse bees, they contaminate food with AFB
What is the treatment or management for AFB in the UK?
- Compulsory destruction of infected colonies under supervision of Bee Inspector.
- The colony will be destroyed after dark, when all the flying bees have returned
- The bees and combs burned and buried in 1m deep pit
- Hives and appliances can be disinfected by scorching with a blow lamp
- Gloves, overalls, footwear and smoker is washed thoroughly in washing soda.
Demonstrate how to hold frames with suspected AFB
- Take out frames of stores to make space.
- Clear frames of bees: Fingers on sides of frame, thumbs over top, shake hard into gap without knocking box
- Know what looks normal and look for the unusual: poor brood pattern, gaps, abnormal larvae and dodgy cappings (remove to investigate)
- Tilt frame to look for reflections on scales.
- If sus, check with a match stick for rope, then burn in smoker
- Photograph unusuals
- If matchstick test test positive, close hive up, reduce entrance to one bee space.
- Contact SBI
- Wash gloves
- Impose a standstill
What are the main ways AFB/EFB are spread and how is it spread within hive. 7
- The Beekeeper cross contaminating thro honey, kit, frames
- Robbing, drifting, swarming
- Migratory beekeeping
- Purchase of infected bees
- Adults not affected. Larvae infected through brood food by nurse bees
- AFB: Infected scales have millions of spores which infects house bees’ mouth parts as they clean. These ar tx by trophillaxis to nurse bees, to larvae in brood food, to adults by trophillaxis and to honey. No impact on adults.
- EFB if a larvae is removed before pupation the infection is removed with it. If larva pupates, it defaecates in cells which house bees later clean out and thus tx bacteria to larvae via brood food and to adults by trophillaxis. No impact on adults.
Why is AFB considered a notifiable disease?
Most destructive brood disease in GB because the spores are very resistant to disinfectant, extremes of heat and cold, retain their powers of germination in honey, old combs kept in store or derelict hives, skeps and boxes for over 35 years.
