The spread of viruses is not well known; however, it is thought that any cross contamination by the beekeeper could spread the disease. Bees ‘drifting’ from hive to hive, contaminated drinking water, contaminated equipment and wind may also transmit the virus.
Honey bees act as a reservoir for the sacbrood virus. Viruses appear to accumulate in the hypopharangeal gland of worker bees, and these bees may transmit the infection to larvae through feeding.
Scientists have yet to determine how the sacbrood virus is transmitted, how the virus persists and why severe outbreaks occur only during the build up season.