1.1.5. Sacbrood virus /Thai sacbrood virus
The clearest symptoms of sacbrood virus (SBV) appear a few days after capping, and consist of non-pupated pale yellow larvae, stretched on their backs with heads lifted up towards the cell opening, trapped in the unshed, saclike larval skin containing a clear, yellow-brown liquid. The virus is also present in adult bees, but without symptoms (Lee and Furgula, 1967; Bailey, 1968). Diseased larvae are most commonly seen in spring, but the disease normally clears quickly with rapid expansion. However, the Asian honey bee, Apis cerana, frequently suffers from lethal sacbrood epidemics caused by a closely related strain of SBV, variously called Thai sacbrood virus (TSBV), Chinese sacbrood virus (CSBV) or Korean sacbrood. The genetic differences of these strains with the SBV infecting A. mellifera are minimal. SBV-infected adults cease to attend brood or eat pollen, start foraging much sooner than normal, and only forage nectar, rarely pollen (Bailey and Fernando, 1972). These may be behavioural adaptations by A. mellifera to prevent sacbrood epidemics, since SBV is shed in the hypopharyngeal secretions fed to larvae and combined with pollen to make bee-bread (Bailey and Ball, 1991).