Deformed wing virus in Apis mellifera L.: prevalence, morphology, and pathogenicity

Viral infections are not considered the most dangerous honeybee ( Apis mellifera L.) diseases though being rather harmful. Virus-caused honeybee pathologies are mainly symptomless (N.J. Dimmock et al., 1987; A.C.F. Hung et al., 1996), nevertheless, a rapid replication of the viruses can be triggered leading to clinical manifestation and even death of the insects (R. Singh et al., 2010). In honeybee families a simultaneous circulation of several viruses can occur. Acute bee paralysis virus (ABPV), deformed wing virus (DWV) in Europe, and Kashmir bee virus (KBV), Israeli acute bee paralysis virus (IABPV) and DWV in the United States seem to be related to honeybee family collapse. This review summarizes the data about one of the most prevalent honeybee viruses, DWV (D. Tentcheva et al., 2004; O. Berènyi et al., 2006; S.L. Nielsen et al., 2008; S. Ruba et al., 2012). Surveys showed DWV in European countries. In Austria, France and Denmark the DWV was found in 91, 97 and 57 % of the apiaries surveyed; in the Czech Republic 31 % of sampled bees were infected with DWV (note, other viruses in Austria and France were less frequent, i.e. 68 and 58 %, respectively, for ABPV; 49 и 86 % for sacbrood virus, SBV; 30 and 86 % for black queen cell virus, BQCV; and 10 and 28 % for chronic bee paralysis virus, CBРV) (D. Tentcheva et al., 2004; O. Berényi et al., 2006). DWV predominated in the apiaries of all studied regions of Russia (A. Kalashnikov et al., 2012), and in Moscow Province only DWV and SBV were revealed. DWV is detected in Apis florea and A. dorsata (X. Zhang et al., 2012). Free DWV dissemination was indicated among some insects other than Apis ( Bombus terrestris, B. pascuorum, B. huntii Green) (E. Genersch et al., 2005; J. Li et al., 2011; A.L. Levitt et al., 2013). DWV, a RNA virus with monocistronic genome, is a member of the genus Iflavirus ( Iflaviridae family, Picornavirales ) (G. Lanzi et al., 2006). Its phylogenetic relationship with Kakugo virus (T. Fujiyuki et al., 2004; A. Rortais et al., 2006) has been confirmed. The identity of the RNA nucleotide sequences of virus isolates from different geographic locations is 98-99 % (O. Berènyi et al., 2007). Its structural proteins VP1-3 are similar to the corresponding picornavirus structural proteins, while a low molecular weight protein VP4 is not found (G. Lanzi et al., 2006). The main targets of deformed wing virus are reproductive organs and digestive tract of bees (Y.P. Chen et al., 2006; J. Fievet et al., 2006). The viral RNA is also found in the wings, head, thorax, hemolymph, fat body (J. Fievet et al., 2006; H.F. Boncristiani et al., 2009). It can be detected during all life stages of honeybee (Y.P. Chen et al., 2005). The brood and adults with clinical manifestations of the disease die (L. Bailey et al., 2010). The worker bees are most sensitive to DWV. The bee colonies are weakened; they are characterized by reduced size and prone to sudden collapse (G. Lanzi et al., 2006; R.M. Johnson et al., 2009). The peak incidence is in the autumn. In addition to vector transmission a horizontal per os and also a vertical transovarial transmission of the virus are possible (C. Yue et al., 2005; C. Yue et al., 2007). The virus can cause a latent infection without visible symptoms of the disease with prolonged persistence of the pathogen in the host and vertical virus transmission or subclinical shorter form with high rate of viral replication and more pathogenic horizontal transmission. For clinical outbreak of DWV infection followed by colony collapse a strong trigger is required, such as immunosuppression by mites Varroa destructor or V. destructor as biological vector. The apiaries with V. destructor infestation are often infected by DWV.