[Explainer] What is Thai sacbrood virus and why does it affect bee colonies in south India?

Apis cerana bees. Photo by Denis Anderson, CSIRO/Wikimedia Commons.

Apis cerana bees. Photo by Denis Anderson, CSIRO/Wikimedia Commons.

  • The Asian honey bee (Apis cerana), more commonly found in South India, is being affected by Thai sacbrood virus (TSBV).
  • Since the disease does not directly affect humans, the research has been slow. But if the spread continues, it might lead to the extinction of the most domesticated species of bees in south India.
  • Though apiary hygiene measures and isolating the queen bees are recommended as solutions, more research is needed to help beekeepers manage the challenge of TSBV.

Thai Sacbrood, a viral disease affecting honey bee colonies, has resurfaced in southern India. The disease, which has been dormant in the southern states for some years, is back and impacting the population of bees especially of the Apis cerana species. This, in turn, can have far-reaching consequences for human life that is indirectly or directly dependant on honey bees.

What is Thai sacbrood virus and how does it work?

Thai sacbrood virus (TSBV) is a variant of sacbrood virus (SBV), a viral disease affecting honey bee colonies. TSBV disease was first observed in Thailand in 1976. In 1991-92, there was an outbreak of the virus in India which resulted in the destruction of more than 90 percent of the then-existing bee colonies in south India. The disease kills bees when they are larvae, thereby reducing the population of bee colonies.

To identify the diseased combs, the combs are observed for any colour change. The colour of the prepupae (the developmental stage before the pupal stage) changes from white to yellow, then to dark brown. Other symptoms include: the presence of prepupae with raised, pointed heads in the comb cells, and dead larvae that turn into ‘sac-like’ structures filled with fluid. At the age of 10 days, they can be easily removed. Sacbrood virus that attacks Apis mellifera is less virulent when compared to TSBV.

Apis cerana honey bees largely found in south India. Photo by Chinmaya KV.
Apis cerana honey bees are largely found in south India. Photo by Chinmaya KV.

What is the significance of Apis cerana bees?

Apis cerana or the Asian honey bee is one of the most domesticated species of honey bees in India and it is important to understand about the ways to protect their population. Bees are very important for the ecosystem. Humans depend on the bees directly (for honey that has antioxidants and anti-inflammatory properties) and indirectly. Bees play a crucial role in pollination. Crops produce good yields if animals and insects help them pollinate. And bees are the most dominant pollinators of fruit, vegetable and crop plants. Data reveals that bees visit around 90 percent of the world’s top 107 crops. In a study published last year in Nature, scientists found evidence that melittin, a component found in honeybee venom, can kill cancer cells.

Apis mellifera, Apis cerana, Apis dorsata, Apis florea and Trigona are the major bee species found in India.  Apis cerana is found mainly in south India. Both farmed and wild bees are responsible for the growth and quality of vegetation. Bees are crucial for food security. However, the population of bees worldwide is in decline. It is essential to protect them and be prepared to tackle the viruses that attack their colonies.

Why do we need to study the virus?

Apiculture is an important source of additional income for farmers and labourers. Beekeeping has become a major occupation in south India since the 20th century. TSBV would also affect the livelihood of many such farmers. Nagendra Sagar, a professional beekeeper and beekeeping demonstrator from Shivamogga, Karnataka, expresses concern over the spread of TSBV saying, “A few years back we discontinued beekeeping due to the outbreak of this virus in south India. The migration of bees from different states could be one reason for this outbreak. Now, we see TSBV active again in the bee colonies of the Western Ghats in Karnataka.”

Sagara adds, “As apiarists, we need more understanding of TSBV to be able to control it. Since it does not affect humans, we speculate that the scientific community is ignoring the spread. So, there is no major research happening in this field.”

It is also crucial that more scientists and researchers work on this, because TSBV may spread to other parts of the world and may not be contained within south India. By studying TSBV we may be warned of the next viruses that may harm the bees too.

Thai Sac Brood virus (TSBV) disease attacking Indian honey bees has been posing threat to hives of Apis cerana. Photo by Chinmaya KV.
Thai Sac Brood virus (TSBV) disease attacking Indian honey bees has been posing a  threat to hives of Apis cerana. Photo by Chinmaya KV.

How do we protect bees from TSBV?

The method most recommended to control the spread of the disease, is to remove the infected honeycombs that contain the dead larvae, and burn them. This virus, also spreads through humans, similar to SARS-COV2. If a person touches infected colonies, and then touches healthy boxes, the virus surges to other boxes as well. It is recommended that the people responsible, always wash their hands with soap before touching new boxes. A recent study suggests isolating the queen bee from the other working bees in the colonies to manage the spread. However, there is no clear protocol to save the honey bees from TSBV.

The Chairman of the Biodiversity Board, Government of Karnataka, Ananth Hegde Ashisar, assures that the scientists will resolve this and come up with a clear solution very soon. He adds, “The Karnataka Biodiversity Board is planning to declare the honey bee as a ‘state insect’, considering its importance in the ecosystem. Regarding the TSBV, we regret to inform you that our scientists and concerned officers are not following it up with the Government and beekeepers. We have informed the concerned minister and officials to look into it.”

Scientific beekeeping and monitoring the viruses in different species of bees are essential to make sure TSBV doesn’t spread any further.


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Banner image: Apis cerana bees. Photo by Denis Anderson, CSIRO/Wikimedia Commons.

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