What Is Sacbrood? A Beekeeper’s Guide

Two beekeepers inspecting a hive for pests and diseases like sacbrood

Sacbrood is a viral infection that affects the Western honey bee (Apis mellifera) and the Eastern honey bee (Apis cerana). Caused by the sacbrood virus (SBV), this bee brood disease is typically a minor inconvenience to colonies. However, it can inflict significant damage on weak or stressed colonies.

What are the symptoms of sacbrood?

There are a range of signs to help beekeepers identify a colony with sacbrood. Many of these signs exist with other hive problems making detection a challenge.

  • Irregular brood pattern: severe cases of sacbrood may have irregular comb patterns, with evidence of scattered dead brood.
  • Unhealthy-looking cell caps: Brood comb caps may have been removed or appear sunken, discolored, or perforated. Take care not to mistake uncapped cells for bald brood, a much less threatening problem.
  • Sick larvae: Bee larvae transform from a glistening pearly white to a yellowish shade. They turn light brown, dark brown, then eventually black. Look for initial discoloration in a larva’s head, which ultimately spreads through the rest of the body.
  • Dead larvae: Beekeepers may identify deceased larvae inside their cells with a fluid-filled skin coating that looks like a plastic sack. They lie fully extended on cell bottoms with their head extended towards the top of the cell in a banana shape. Their wrinkled form may have also formed brittle scales on the cell’s lower walls.
  • Odor: Advanced sacbrood may produce an unpleasant, foul smell.
Macro photograph of a bee larva infected with sacbrood
Larvae with sacbrood form a fluid filled sack that can easily be removed from the cell.

How does sacbrood spread?

The sacbrood virus survives up to four weeks on honey, pollen, nectar, larval remains, and water. Foraging worker bees may encounter these sources during their daily travels, then unintentionally bring them back to the hive.

Once inside the colony, adults can contract the virus, while nurse bees may feed contaminated food sources to their developing babies.

Beekeepers also spread sacbrood by moving between hives using infected tools and equipment. Combining colonies will transfer the disease to healthy bees.

Bees also spread SBV through drifting, robbing, and swarming.

Recommended reading: What are some of the biggest threats to honey bees.

How to treat sacbrood

Healthy hives will usually deal with sacbrood through their everyday housekeeping activities. It doesn’t have the same crippling effect as brood diseases like American foulbrood. Check out the symptoms of American foulbrood here.

Stressed and struggling hives may need help to shrug off this virus. In extreme infections, beekeepers can re-queen and introduce young, healthy bees while replacing combs.

Reduce unused space in the hive by removing a super. Consider feeding the bees sugar syrup or pollen if foraging conditions are poor.

In 2016, the Veterinary Medicines Directorate sponsored a Fera study on antivirals against bee viruses, DWV and CBPV. Though these antivirals showed promise, they have yet to be tested on sacbrood or in actual field conditions.

Closeup of a dead larva with sacbrood virus
A larva with sacbrood that has been removed from its cell. It looks like a fluid filled sack.

Prevention options

Beekeepers can reduce the likelihood of SBV implementing proper hive hygiene practices. Regularly cleaning hive tools and equipment will help prevent the spread.

Choosing the right breed of bee will also help prevent sacbrood and other threats. Russian or Italian bees have excellent housekeeping practices and may be worth considering for your hive.

Removing diseased brood and keeping the colony strong by providing supplemental feeding also helps. Starving bees struggle to fight off threats in any form.

6 fast facts about sacbrood

  1. Workers, larvae, and occasional drones are affected by the virus.
  2. 2-day old larvae are most susceptible to the disease.
  3. Infected adult bees exhibit no apparent symptoms but have a shorter lifespan.
  4. The queen won’t typically lay eggs near infected brood comb.
  5. Granular fluid builds up between the larvae and the sacbrood skin.
  6. Once the cell is sealed, diseased larvae die before reaching the pupal stage. 

Related reading:

Commonly asked questions

Sacbrood vs. black queen cell virus

Sacbrood and black queen cell virus both turn bee larvae a yellowish color and develop a plastic-like appearance around them. But SBV affects bees at adult and larval phases while BQCV kills developing queen pupae.

What is Thai sacbrood?

Thai sacbrood is a viral disease that impacts honey bees. Discovered in 1976 in Thailand, it is a variant of sacbrood that is a significant threat to Asian bee populations. While SBV has minimal impact on colony numbers of Apis mellifera, TSBV has devastated Apis cerana colonies throughout parts of Asia.

Sacbrood vs. American foulbrood

Sacbrood and American foulbrood are both diseases that impact honey bee brood. Although their symptoms are similar, larval cells inflicted by AFB will rope out during the matchstick test – sacbrood-infested cells will not. AFB is a bacterial disease, while sacbrood is a viral infection.

Sacbrood vs. European foulbrood

While both diseases impact honey bee brood comb, European foulbrood impacts larvae in open brood while sacbrood impacts larvae in sealed cells. Source

Can sacbrood affect humans?

Sacbrood is specific to honeybees and doesn’t pose any risk to humans.

Can the Sacbrood virus survive outside the hive?

The virus survives outside the hive for around four weeks.

Do all strains of honeybees respond the same way to a Sacbrood infection?

Susceptibility to sacbrood varies among honeybee strains. Selectively bred lines exhibit increased resistance through more hygienic behavior.

What is the risk period for sacbrood?

Sacbrood disease may appear at any time of the year but more often during the brood-rearing season.

Does weather or climate affect Sacbrood outbreaks?

While sacbrood can appear in various climatic conditions, some beekeepers observe more cases during cool and damp weather periods. Stress on the colony, potentially due to unfavorable weather, can make them susceptible.

Did you know? In 1913, GF White found that heating honey to at least 158°F (70°C) for ten minutes inactivated sacbrood. Exposing it to direct sunlight at room temperature for five to six hours got the same result. Additionally, the virus in decomposing larvae is destroyed faster due to putrefaction, taking seven to ten days to destruct. Reference: White GF. Sacbrood, a disease of bees. U.S. Department of Agriculture, Bulletin of Entomology 1913; Circular No. 169.

Interesting research

Authors: Wei R, Cao L, Feng Y, Chen Y, Chen G, Zheng H.

Summary: Sacbrood virus (SBV) affects both Western (Apis mellifera) and Eastern honeybees (Apis cerana). New findings show that SBV can transmit between species, especially among wild pollinators.

This suggests that the virus has a broader host range than previously thought. It raises concerns about the sustainability of agriculture and ecosystem resilience.

For decades, numerous studies have explored SBV’s effects on honeybees. Advancements have been made in understanding its epidemiology, pathogenesis, transmission, and symptoms in honeybees and other pollinators. In Asia, Chinese medicine has been used to combat sacbrood disease in A. cerana.

This review aimed to consolidate knowledge on SBV, identify knowledge gaps, and propose future research directions and management strategies to curb this detrimental disease.

Summary of treatment options for sacbrood:

1. Colony Management:

No chemical treatments exist for SBV. Beekeepers should limit the use of chemical drugs because they can remain in honeybee products.

Best approach: manage bee colonies to prevent the disease.

  • Remove extra hive boxes to reduce unused hive space.
  • If the disease appears, remove combs with diseased brood and clean hives to stop the virus from spreading.
  • A queen bee can pass the virus to her young. So, replace her with a healthy one or prevent her from laying eggs for up to 14 days to help the colony recover.
  • Make sure the bees are well-nourished.

2. RNA Interference (RNAi):

  • RNAi is a natural process that stops genes from working.
  • Honeybees use RNAi as a primary defense against viruses.
  • Introducing specific RNA into bees can activate this defense and treat the virus.
  • This method is very effective but expensive, and there are some concerns about using it widely.

3. Antibody Treatment:

Honeybees don’t naturally produce antibodies against viruses.

Scientists made an antibody which helped fight the virus in tests. It could be a new way to control the virus.

4. Herbal Medicines:

Some plants have properties that can fight against diseases. Chinese herbs have been found helpful against sacbrood disease.

One herb, indigowoad root, showed promising results in the lab. It increased the survival of infected bees. Though herbs show potential, more research is needed to understand how they work.

Read the full research>

Authors: Kim, C., Kim, J-M, Choi, H., Choi, Y-S, Jin, B-R, Lee, K-S, & Choi, K.

Summary: While bees are a crucial part of the pollination process, many wild bees worldwide are disappearing.

Scientists found that microbes living inside a bee’s stomach might help them stay healthy and fight off diseases. Bees that get sick from a virus may have different microbes than the bees that don’t get sick.

The researchers discovered that healthy bees have a more diverse mix of microbes.

Read the full research>

Image attribution: “Courtesy The Animal and Plant Health Agency (APHA), Crown Copyright”. Sourced from BeeBase Gallery.

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