1.1. Honey bee viruses
There are currently about 24 viruses identified in honey bees, whose physical and biological properties are described in Table 1 and Table 2 respectively. Most of these were discovered by Bill Bailey, Brenda Ball and colleagues at Rothamsted Experimental Station, UK during the 1960s-1980s (Bailey and Ball, 1991; Ribière et al., 2008). More recent additions have come mostly from mass sequencing of RNA and DNA from whole bee extracts (Fujiyuki et al., 2004; Cox-Foster et al., 2007; Cornman et al., 2010; Runckel et al., 2011), and it may well be that there is overlap between the traditionally described viruses and these newly described viral sequences. Several viruses are also closely enough related to be regarded as members of a single species complex (DWV/VDV-1/EBV; ABPV/KBV/IAPV; SBV/TSBV; BVX/BVY and LSV-1/LSV-2), reducing the total to around 16-18 truly unique viruses.
Although some viruses produce recognizable symptoms at sufficiently elevated titres, honey bee viruses generally persist naturally in honey bee populations at low levels, without causing overt symptoms, using a variety of transmission routes (Fig. 1; Table 2). Symptoms are, however, still the principal method by which diseases are diagnosed in the apiary. The advantages of symptom-based diagnosis are that it is robust, simple, fast and cheap and for some diseases accurate. The major disadvantages are that:
- many virus infections do not present visible symptoms at all times
- not all life stages present symptoms
- often different viruses produce similar symptoms (e.g. paralysis)
- a single virus may present different symptoms (e.g. CBPV)
- symptoms can be
confounded if multiple virus infections are present
All viruses are asymptomatic at lower levels of infection and most shorten the life span of bees to varying degrees. The diagnostic symptoms for the major virus diseases have been described in detail by Bailey and Ball (1991) and can be summarized as follows:
Fig. 1. Diagram describing the different possible transmission routes for honey bee viruses. Adapted from de Miranda et al. (2011).