Deformed Wing Virus
Encyclopedia
Deformed wing virus 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.
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.
. 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.
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.
, 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.
RNA virus
An RNA virus is a virus that has RNA as its genetic material. This nucleic acid is usually single-stranded RNA but may be double-stranded RNA...
, one of 18 known viruses affecting the honey bee
Honey bee
Honey bees are a subset of bees in the genus Apis, primarily distinguished by the production and storage of honey and the construction of perennial, colonial nests out of wax. Honey bees are the only extant members of the tribe Apini, all in the genus Apis...
, Apis mellifera. The virus was first isolated from a sample of symptomatic honeybees from Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
in the early 1980s and is currently distributed worldwide.
Genomics
The viral genome was published in 2006. 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
Cytosine
Cytosine is one of the four main bases found in DNA and RNA, along with adenine, guanine, and thymine . It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached . The nucleoside of cytosine is cytidine...
, 22.4% guanine
Guanine
Guanine is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine . In DNA, guanine is paired with cytosine. With the formula C5H5N5O, guanine is a derivative of purine, consisting of a fused pyrimidine-imidazole ring system with...
and 32.3% uracil
Uracil
Uracil is one of the four nucleobases in the nucleic acid of RNA that are represented by the letters A, G, C and U. The others are adenine, cytosine, and guanine. In RNA, uracil binds to adenine via two hydrogen bonds. In DNA, the uracil nucleobase is replaced by thymine.Uracil is a common and...
. 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 mitesVarroa destructor
Varroa destructor is an external parasitic mite that attacks honey bees Apis cerana and Apis mellifera. The disease caused by the mites is called varroatosis....
. 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 destructorVarroa destructor
Varroa destructor is an external parasitic mite that attacks honey bees Apis cerana and Apis mellifera. The disease caused by the mites is called varroatosis....
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
Colony Collapse Disorder
Colony collapse disorder is a phenomenon in which worker bees from a beehive or European honey bee colony abruptly disappear. While such disappearances have occurred throughout the history of apiculture, the term colony collapse disorder was first applied to a drastic rise in the number of...
.
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 virusKakugo
Kakugo or Kakugo RNA is a Picorna-like virus, which is most commonly found in the brains of worker bees. The Kakugo virus, when resident in a bee's brain, can contribute to aggressive behaviors such as are preeminent during a bee's guard phase in their life cycle...
, has an RNA sequence that is 98% similar to DWV. It is found only in the mushroom bodies
Mushroom bodies
The mushroom bodies or corpora pedunculata are a pair of structures in the brain of insects and other arthropods.-Structure:Mushroom bodies are usually described as neuropils, i.e. as dense networks of neuronal processes and glia...
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.