during 20092011 , six ( 5 male and 1 sex unknown ) adult big brown bats ( eptesicus fuscus ) were brought to a wildlife hospital and rehabilitation center ( paws wildlife center , lynnwood , wa , usa ) during late spring or summer because they could not fly . all but 1 of the bats had > 1 visibly swollen and occasionally contused joints involving the long bones of the legs and wings ; 1 had contusions of the oral commissures . however , minimal or no clinical improvement was observed , and the bats showed progressive joint swelling and increased lethargy . bat tissues were sent to a facility that specializes in the pathologic analysis of nondomestic species ( northwest zoopath , monroe , wa , usa ) for further investigation . histologic examination showed severe fibrino - suppurative and necrotizing tenosynovitis and osteoarthritis that involved the long bones and occasionally facial flat bones and joints with occasional localized vasculitis . no bacterial or fungal agents were seen by light microscopy of specimens stained with hematoxylin and eosin , giemsa , warthin - starry , brown and brenn , or gomori methenamine silver stains or in a wright - giemsa  stained cytologic preparation of a joint aspirate . cultures for aerobic and anaerobic bacteria , and cultures of the joint from 1 bat for mycoplasma showed negative results . thin - section electron microscopy of synovial tissue extracted from a wax histoblock showed poxvirus particles in inflammatory cells ( figure 1 , panel a ) . a 906e transmission electron microscope ( carl zeiss , peabody , ma , usa ) at an accelerating voltage of 80 kv was used for initial imaging . digital images were captured by using a 2k  2k camera ( advanced microscopy techniques , danvers , ma , usa ) . the state veterinarian and the centers for disease control and prevention ( atlanta , ga , usa ) were subsequently consulted . a ) electron micrograph of poxvirus particles in synovium of a big brown bat , northwestern united states . material was taken from the wing and joint of an affected bat for real - time pcr testing and cell culture isolation . wing and joint material was positive by real - time pcr for a poxvirus with low genomic g + c content ( 7 ) . the elbow joint of 1 bat was then processed for poxvirus growth in cell culture . the specimen was emulsified in 500 ml of sterile phosphate - buffered saline by using a tissue grinder . viral nucleic acid was extracted by using ez1 advanced xl ( qiagen , valencia , ca , usa ) . ten microliters of homogenate was added to 1 ml of rpmi 1640 medium supplemented with 2% fetal bovine serum , l - glutamine , and penicillin / streptomycin . growth medium from a t25 flask containing green monkey kidney epithelial cells ( bsc40 ) was removed and the virus mixture added . the flask was incubated for 1 hour at 56c , after which 6 ml of rpmi 1640 medium was added to each flask . two microliters of supernatant was pipetted onto a 300-mesh formvar - carbon  coated nickel grid . after a 10-min incubation , supernatant was blotted and the grid was rinsed . a negative stain composed of 5% ammonium molybdate , ph 6.9 , and 0.1% trehalose ( wt / vol ) was briefly applied to the grid and blotted . the grid contents were visualized by using a tecnai biotwin electron microscope ( fei company , hillsboro , or , usa ) operating at 120 kv . digital images were captured by using a 2k  2k camera ( advanced microscopy techniques ) . poxvirus particles were identified in cell culture supernatant ( figure 1 , panel b ) . genome sequencing produced data that were used to construct a phylogenetic tree ( figure 2 ) . dna sequences from 7 open reading frames ( a7l , a10l , a24r , d1r , d5r , h4l , and j6r , according to reference sequence vaccinia virus copenhagen ) were extracted on the basis of sequence similarity . open reading frames were translated into amino acid sequences and aligned by using the clustalw alignment option in geneious version 6.0.5 ( www.geneious.com/ ) . the tree search was conducted by using mrbayes in geneious 6.0.5 under default settings and amsacta moorei ( red hairy caterpillar ) entomopoxvirus ( moyer ) was used as the outgroup with a burn in of 10% . maximum clade credibility tree generated by mrbayes in geneious version 6.0.5 ( www.geneious.com/ ) using amino acid sequences from 7 open reading frames ( final chain length 240,000 at an average sd of split frequencies of zero ) for poxviruses . clade credibility values are indicated at each node.the virus isolated in this study is shown in boldface . amsacta moorei ( red hairy caterpiller ) entomopoxvirus ( moyer ) was used as the outgroup . historically , osteomyelitis with arthritis has been reported in smallpox patients ( osteomyelitis variolosa ) and in smallpox vaccine recipients ( vaccinia osteomyelitis ) , but did not occur frequently ( 8) . in such cases , variola virus particles were detected in joint fluid ( 9 ) , and vaccinia virus was isolated from a bone biopsy specimen of an affected limb ( 10,11 ) . it is unclear whether the manifestation of arthritis in bats is a normal or rare result of the infection , or a new development in the evolution of the virus . likewise , the frequency of poxvirus infection in big brown bats is impossible to estimate at this stage . because the public is generally cautioned against handling downed bats because of possible rabies infection , underestimation of prevalence is likely . infectious disease surveys of bats might have missed the infection up to this point because no obvious lesions are apparent on the skin , and swollen joints might have been classified as being arthritis without suspicion of infectious disease involvement . results of at least 3 investigations that involved detection of viral dna detection in bat guano have been published ; 2 involved bats from north america and 1 involved bats in china ( 1214 ) . the zoonotic potential or host range of the virus described herein is not known , but at a minimum , the virus could pose a newly emergent threat to bat populations . likewise , it is not clear if the infection seen in bats is a result of spillover or possibly an introduction of the virus into a new area . the isolate does not group with any of the 8 characterized genera of chordopoxvirus ; its nearest neighbor is cotia virus , an as yet unclassified chordopoxvirus first isolated from sentinel suckling mice in a state reserve in cotia county , so paulo state , brazil , in 1961 ( 15 ) . although the 2 viruses are nearest neighbors , levels of shared nucleotide and amino acid identity between them suggest they should likely be considered separate genera ( table , appendix ) . we propose that the bat - derived isolate be distinguished as part of a new lineage with the suggested genus designation chiropoxvirus . further efforts should be undertaken to determine whether cotia virus should be included in this genus . the bat - derived virus requires a new species designation for which we propose eptesipox virus because of its isolation from an eptesicus fuscus bat specimen . * values above the diagonal are for nucleotide comparisons and values below the diagonal are for amino acid comparisons . myx , myxoma virus ; rfv , rabbit fibroma virus ; swp , swinepox virus ; gtp , goatpox virus ; spp , sheeppox virus ; lsd , lumpy skin disease virus ; dpv , deerpox virus ; yld , yaba - like disease virus ; ymt , yaba monkey tumor virus ; epp , eptesipox virus ; ctv , cotia virus ; cpx , cowpox virus ; ect , ectromelia virus ; hsp , horsepox virus ; skp , skunkpox virus ; var , variola virus ; rac , raccoonpox virus ; vpx , volepoxvirus ; moc , molluscum contagiosum virus ; cnp , canarypox virus ; fwp , fowlpox virus ; crv , crocodilepox virus ; bps , bovine papular stomatitis virus ; orf , orf virus .
a wildlife hospital and rehabilitation center in northwestern united states received several big brown bats with necrosuppurative osteomyelitis in multiple joints . 
 wing and joint tissues were positive by pcr for poxvirus . 
 thin - section electron microscopy showed poxvirus particles within a - type inclusions . 
 phylogenetic comparison supports establishment of a new genus of poxviridae .