- Deformed wing virus
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Deformed wing virus Virus classification Group: Group IV ((+)ssRNA) Order: Picornavirales Family: Iflaviridae Genus: Iflavirus Species: Deformed wing virus Deformed wing virus (DWV) is an RNA virus, one of 18 known viruses affecting the honey bee, Apis mellifera. The virus was first isolated from a sample of symptomatic honeybees from Japan in the early 1980s and is currently distributed worldwide.
Contents
Genomics
The viral genome was published in 2006.[1] The genome is 10140 nucleotides in length excluding the poly(A) tail and contains a single large open reading frame encoding a 328-kilo Dalton (kDA) polyprotein. 5' of the central coding sequence is a 1144-nucleotide nontranslated leader sequence (UTR). 3' coding sequence is a 317-nucleotide nontranslated region which is followed by a poly(A) tail.
The genome is 29.5% adenosine, 15.8% cytosine, 22.4% guanine and 32.3% uracil. Analysis of codon use found 39.5% uracil and 26.8% adenosine in the third base position.There are three major structural proteins - VP1 (44 kDa), VP2 (32 kDa), and VP3 (28 kDa). These lie in the N-terminal section of the polyprotein. The C-terminal part of the polyprotein contains sequence motifs typical of well-characterized picornavirus nonstructural proteins: an RNA helicase, a chymotrypsin-like 3C protease and an RNA-dependent RNA polymerase.
VP1 is encoded between codons 486 to 880 and VP3 lies between codons 913 and 1063. The boundaries of VP2 are not as well defined but it is encoded 5' of VP1. There may be a small protein (VP4) encoded between codons 464 and 486 but this protein has not been confirmed to be present in the genome.
Lying 5' to VP2 is a very variable leader peptide (L protein). Despite occupying 7.3% of the polyprotein it is responsible for 26.2% to 33.3% of the variation found between the Iflaviridae. It may be involved in the inhibition of host cap-dependent mRNA translation and stimulation of viral internal ribosome entry site activity.
VPg, a small protein (23 amino acids) common to many RNA viruses, is responsible for stabilizing the 5' end of the genomic RNA for replication and translation. A putative VPg is present between nucleotide positions 2093 and 2118 immediately 5' of the 3C protease. The protein itself has not yet been confirmed to be present in the viron.
The helicase domains A, B and C are found between codons 1460 and 1575. The 3C protease domains span codons 2183 to 2327. The usual eight RdRp domains are located between codons 2493 and 2828.
The genome structure is
5'UTR-L-VP2-(VP4)-VP1-VP3-RNA helicase-(VPg)-3C protease-RNA dependent RNA polymerase-3'UTR
The putative VP4 and VPg proteins are marked here by parentheses. If the VPg is present in the genome a copy will be bound to the 5' end of the RNA genome.
Molecular biology
The viron is a 30-nm icosahedral particle consisting of the single positive-stranded RNA genome and three major structural proteins.
Virology
The virus is concentrated in the heads and abdomens of infected adult bees with significantly reduced titers in the thorax. The genome is detectable by reverse transcriptase-polymerase chain reaction in the head, thorax, abdomen and wings of infected bees. Only the legs are devoid of virus.
Symptoms
Deformed wing virus (DWV) is suspected of causing the wing and abdominal deformities often found on adult honeybees in colonies infested with Varroa mites. These symptoms include damaged appendages, particularly stubby, useless wings, shortened, rounded abdomens, miscoloring and paralysis. Symptomatic bees have severely reduced life-span (less than 48 hours usually) and are typically expelled from the hive. The symptoms are strongly correlated with elevated DWV titres, with reduced titres in asymptomatic bees from the same colonies. In the absence of mites the virus is thought to persist in the bee populations as a covert infection, transmitted orally between adults (nurse bees) since the virus can be detected in hypopharyngeal secretions (royal jelly) and broodfood and also vertically through the queen's ovaries and through drone sperm. The virus may replicate in the mite but this is not certain.
Transmission by Varroa destructor
The severe symptoms of DWV infections appear to be associated with Varroa destructor infestation of the bee hive and studies have shown that Varroa destructor harbors greater levels of the virus than are found even in severely infected bees. Thus V. destructor may not only be a concentrating vector of the virus but may also act as a replicating incubator, magnifying and increasing its effects on the bees and on the hive. The combination of mites and DWV causes immunosuppression in the bees and increased susceptibility to other opportunistic pathogens and has been considered a significant factor in honey bee colony collapse disorder.
The virus may also be transmitted from queen to egg and in regurgitated food sources, but in the absence of V. destructor this does not typically result in large numbers of deformed bees.
DWV impairs cognitive functions
The artificial infection of this virus is also reported to cause specific deficits in behavioural plasticity of honeybee. Honeybees are more sensitive to lowest stimuli and show impairment in their associative conditioning. Interestingly the non-associative learning remains intact. Thus DWV seems to interfere with molecular mechanism of learning that may include immune system and signalling pathways.
Kakugo virus and aggressive behavior
Another virus, the Kakugo virus, has an RNA sequence that is 98% similar to DWV. It is found only in the mushroom bodies of aggressive, guard honeybees. Bees that are significantly affected by DWV also have measurable titers of the virus in their heads while bees that are symptomless only produce titers in their abdomens or thoraxes. Some researchers have detected increased aggressiveness immediately before colony collapse, and suspect that the virus may play a role. Other researchers have dismissed this relationship.
References
- ^ Lanzi G., de Miranda J.R., Boniotti M.B., Cameron C.E., Lavazza A., Capucci L., Camazine S.M., Rossi C. (2006) Molecular and biological characterization of deformed wing virus of honeybees (Apis mellifera L.). J Virol. 2006 80(10):4998-5009
- Deformed Wing Virus and Honey Bee Queens
- Iqbal,J; Mueller, U (June 2007). "Virus infection causes specific learning deficits in honeybee foragers". Proc Biol Sci. 274 (1617): 1517–1521. doi:10.1098/rspb.2007.0022. PMC 2176156. PMID 17439851. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2176156.
- Fievet, J; Tentcheva, D; Gauthier, L; De, Miranda, J; Cousserans, F; Colin, Me; Bergoin, M (March 2006). "Localization of deformed wing virus infection in queen and drone Apis mellifera L" (Free full text). Virology journal 3: 16. doi:10.1186/1743-422X-3-16. PMC 1475838. PMID 16569216. http://www.virologyj.com/content/3//16.
- Fujiyuki, T.; Takeuchi, H; Ono, M; Ohka, S; Sasaki, T; Nomoto, A; Kubo, T (2004). "Novel Insect Picorna-Like Virus Identified in the Brains of Aggressive Worker Honeybees". Journal of Virology 78 (3): 1093. doi:10.1128/JVI.78.3.1093-1100.2004. PMC 321398. PMID 14722264. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=321398.
- Ongus, Jr; Peters, D; Bonmatin, Jm; Bengsch, E; Vlak, Jm; Van, Oers, Mm (December 2004). "Complete sequence of a picorna-like virus of the genus Iflavirus replicating in the mite Varroa destructor" (Free full text). The Journal of general virology 85 (Pt 12): 3747–55. doi:10.1099/vir.0.80470-0. PMID 15557248. http://vir.sgmjournals.org/cgi/pmidlookup?view=long&pmid=15557248.
- Yue, C; Schröder, M; Gisder, S; Genersch, E (August 2007). "Vertical-transmission routes for deformed wing virus of honeybees (Apis mellifera)". The Journal of general virology 88 (Pt 8): 2329–36. doi:10.1099/vir.0.83101-0. PMID 17622639.
- Yang, X; Cox-Foster, Dl (May 2005). "Impact of an ectoparasite on the immunity and pathology of an invertebrate: evidence for host immunosuppression and viral amplification" (Free full text). Proceedings of the National Academy of Sciences of the United States of America 102 (21): 7470–5. doi:10.1073/pnas.0501860102. PMC 1140434. PMID 15897457. http://www.pnas.org/cgi/pmidlookup?view=long&pmid=15897457.
- Chen, Yp; Pettis, Js; Collins, A; Feldlaufer, Mf (January 2006). "Prevalence and transmission of honeybee viruses" (Free full text). Applied and environmental microbiology 72 (1): 606–11. doi:10.1128/AEM.72.1.606-611.2006. PMC 1352288. PMID 16391097. http://aem.asm.org/cgi/pmidlookup?view=long&pmid=16391097.
- Fievet, J; Tentcheva, D; Gauthier, L; De, Miranda, J; Cousserans, F; Colin, Me; Bergoin, M (March 2006). "Localization of deformed wing virus infection in queen and drone Apis mellifera L" (Free full text). Virology journal 3: 16. doi:10.1186/1743-422X-3-16. PMC 1475838. PMID 16569216. http://www.virologyj.com/content/3//16.
- Lanzi, G; De, Miranda, Jr; Boniotti, Mb; Cameron, Ce; Lavazza, A; Capucci, L; Camazine, Sm; Rossi, C (May 2006). "Molecular and biological characterization of deformed wing virus of honeybees (Apis mellifera L.)" (Free full text). Journal of virology 80 (10): 4998–5009. doi:10.1128/JVI.80.10.4998-5009.2006. PMC 1472076. PMID 16641291. http://jvi.asm.org/cgi/pmidlookup?view=long&pmid=16641291.
- Yue, C; Genersch, E (December 2005). "RT-PCR analysis of Deformed wing virus in honeybees (Apis mellifera) and mites (Varroa destructor)" (Free full text). The Journal of general virology 86 (Pt 12): 3419–24. doi:10.1099/vir.0.81401-0. PMID 16298989. http://vir.sgmjournals.org/cgi/pmidlookup?view=long&pmid=16298989.
Categories:- Viruses
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