Sacbrood Virus

SBV

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Changed on: 04.06.2019
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Sacbrood is a viral condition that affects bee broods. The virus can also be detected in adult bees and is passed on by them. The sacbrood virus (SBV) is round, with a diameter of 28 nanometre (1 nm = one millionth of a meter) and was discovered by Bailey in 1964. It infects fat and muscle cells and the trachea cells of larvae, as well as cells in the neural tissue and the hypopharynx gland of adult bees. Larvae become infected after feeding from contaminated food produced by worker bees with undetected infections.

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Sacbrood is a viral condition that affects bee broods. The virus can also be detected in adult bees and is passed on by them. The sacbrood virus (SBV) is round, with a diameter of 28 nanometre (1 nm = one millionth of a meter) and was discovered by Bailey in 1964. It infects fat and muscle cells and the trachea cells of larvae, as well as cells in the neural tissue and the hypopharynx gland of adult bees. Larvae become infected after feeding from contaminated food produced by worker bees with undetected infections.

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Symptoms

Spotted brood chamber, caps are cracked, punctured or sunk-in, left-over capped or uncapped brood cells. The pre-pupa dies, it takes on a sac-like shape (liquid gathers between the old larva and the pupa skin, while the dead larva decomposes, giving it a grainy character.)

The larva can be pulled from the cell with a pair of tweezers, like a sac. The larva disintegrates into a watery-grainy pulp; the colour of the larva becomes increasingly darker (from head to end), its head curls up as the body dries to a blackish-brown scale with the head bent upwards (“Chinese Slippers”). The scale lies loose at the bottom of the cell (the original segmentation of the larva is still visible in most cases), no typical odour.

Effects on the bee colony:  loss of brood, shortened lifespan. Infected young bees will not fulfil their task of feeding the larvae and prematurely turn into foraging bees that will not gather pollen in most cases. If they still gather pollen, the risk of infection is very high for young nursing bees; degeneration of hypopharyngeal glands (bees do not feed on pollen anymore).

Transmission

Young worker bees are the most susceptible to infection, as the main transmission route seems to be feeding. Transovarial transmission by an infected bee queen is also possible. Transmission can be initiated in a laboratory experiment (e.g. injecting virus particulates). Additionally, transmission can also be caused by feeding contaminated larvae food-- in particular, pollen. Evidence of SBV can also be found in honey and royal jelly. Worker bees are infected by removing infected larvae and brood rearing. The role of the varroa mite in transmitting sacbrood is still unclear (experimental transmission via injecting some SBV particles into pupa is possible).

The causes of transmissions between colonies are the beekeeper (replacing combs) or landing at the wrong hive and robbery.

Prevention

A permanent source of nectar should be available: food availability in the colony should never be interrupted so that the larvae get sufficient supplies  as spontaneous recovery is possible if the nectar flow is good (depending on the hygiene behaviour of the bees that remove dead brood). Additional feeding during gaps in the nectar flow (colonies lacking food supplies are more susceptible). Promote cleaning, decrease verroa infestation levels, as sacbrood is a by-product of varoosis.

There is no medication to control sacbrood.


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