influenza viruses were isolated in madin - darby canine kidney cells from lung tissue or nasal swab samples from pigs of various ages ( young growers to adults ) manifesting influenzalike illness ( ili ) in manitoba in january ( a / swine / manitoba/12707/05 ) , alberta in february ( a / swine / alberta/14722/05 ) , british columbia in may ( a / swine / british columbia/28103/05 ) , and ontario in july ( a / swine / ontario/33853/05 ) . a / ontario / rv1273/05 was isolated in primary rhesus monkey kidney cells from a nasal swab specimen collected as part of a diagnostic workup from an otherwise healthy farm worker in ontario in whom ili developed 23 days after onset of ili among pigs on his premises . fourteen - day courses of oseltamivir therapy were prescribed for this patient beginning the day he saw his physician and for 11 other potentially exposed farm workers beginning 2 days later . a / turkey / ontario/31232/05 was isolated in embryonated hen 's eggs from a cloacal swab sample from turkeys showing a severe drop in egg production . the turkey farm was located across the road from a swine farm at which pigs concurrently exhibited ili , although virus isolates were not available from those pigs . nucleotide sequences of the full - length coding regions of all 8 rna segments from each virus were determined by direct cycle sequencing with previously described techniques and primers ( 3,10,11 ) . related reference viruses were identified by blast ( basic local alignment search tool ) analyses , sequence comparisons were conducted by using dnastar software , version 6.3 ( dnastar inc . , madison , wi , usa ) , and phylogenetic relationships were estimated from the nucleotide sequences by the method of maximum parsimony ( fast heuristic search algorithm , paup software , version 4.0b10 [ sinauer associates , inc . , sunderland , ma , usa ] ) with a bootstrap resampling method ( 200 replications ) . pairwise nucleotide identities among the 2005 canadian swine , turkey , and human isolates range from 94.0%100% ( na ) to 99.9%100% ( m ) , and amino acid identities range from 98.9%100% ( na ) to 100% ( m , np ) . the human and swine isolates recovered on a single farm in ontario are 100% identical in nucleotide sequences across all 8 rna segments . phylogenetically , the 2005 canadian viruses form single clusters on phylograms for each of the 8 viral rna segments , confirming that this epizootic was caused by a single lineage of viruses . all of the viruses share the same human / classical swine / avian triple reassortant genotype as the h3n2 viruses that emerged in pigs in the united states in 1998 ( 24 ) . the ha genes ( figure 1 ) of the canadian viruses are most closely related to the cluster iii group of american viruses that were first isolated from pigs in 1999 ( 4 ) and subsequently from turkeys ( 7,8 ) , though the ha phylogram topography suggests that these canadian and related us viruses represent a new , separate cluster ( iv ) of viruses . the m , np , ns , and polymerase genes of the canadian viruses are also phylogenetically closely related to reassortant viruses dating back to 1998 in the united states ( data not shown ) . in contrast , the na genes ( figure 2 ) of the 2005 canadian viruses , though still clearly of human lineage , are phylogenetically distinct from most of the us swine and turkey isolates . this lineage is represented by human h3n2 isolates from asuncin , paraguay , ( 2001 ) and new york ( 2003 ) . however , this lineage of na genes has also been introduced into animal influenza viruses on 2 previous occasions . the first is represented by a / turkey / ohio/313053/04 ( 8) , which phylogenetically is the most closely related virus to the canadian viruses across all 8 rna segments . since this virus was isolated in february 2004 ( 8) , nearly 1 year before the first isolations of viruses from canada , one might conjecture that this or a closely related virus from the united states was the source of the canadian viruses . however , this lineage of na genes was also already present in human / classical swine reassortant h1n2 viruses ( a / swine / ontario/48235/04 , a / swine / ontario/55383/04 ) isolated from canadian pigs in 2004 ( 12 ) . thus , it is neither possible nor prudent from the phylogenetic data alone to define the specific epidemiologic source(s ) of the 2005 canadian h3n2 viruses . however , the appearance of this lineage of na genes among h3n2 viruses in turkeys in the united states and canada and h3n2 and h1n2 viruses in pigs in canada suggests that a complicated web of interspecies transmission , reassortment , and transboundary movement of viruses occurred in a relatively short period of time . nucleotide phylogram for the hemagglutinin ( ha ) genes of a / swine / manitoba/12707/05 , a / swine / alberta/14722/05 , a / swine / british columbia/28103/05 , a / swine / ontario/33853/05 , a / turkey / ontario/31232/05 , a / ontario / rv1273/05 , and related reference viruses . the evolutionary relationships among these viruses were estimated by the method of maximum parsimony ( paup software , version 4.0b10 ) with a bootstrap resampling method ( 200 replications ) and a fast heuristic search algorithm . horizontal - line distances are proportional to the minimum numbers of nucleotide changes needed to join nodes and gene sequences . the designations i , ii , and iii identify clusters of viruses previously defined among triple reassortant swine viruses in the united states ( 4 ) . the viruses described in this report and related viruses are proposed to represent a new cluster iv group of viruses . genbank accession numbers for the sequences of all reference viruses are provided in parentheses after the virus names . nucleotide phylogram for the neuraminidase ( na ) genes of a / swine / manitoba/12707/05 , a / swine / alberta/14722/05 , a / swine / british columbia/28103/05 , a / swine / ontario/33853/05 , a / turkey / ontario/31232/05 , a / ontario / rv1273/05 , and related reference viruses . the evolutionary relationships among these viruses were estimated by the method of maximum parsimony ( paup software , version 4.0b10 ) with a bootstrap resampling method ( 200 replications ) and a fast heuristic search algorithm . horizontal - line distances are proportional to the minimum numbers of nucleotide changes needed to join nodes and gene sequences . genbank accession numbers for the sequences of all reference viruses are provided in parentheses after the virus names . to our knowledge , this report describes the first isolation of a human / classical swine / avian triple reassortant h3n2 virus from a human . this isolation could not have occurred through cross - contamination in a laboratory since the animal and human virus isolations and sequencing were conducted in different locations . hemagglutination - inhibition ( hi ) and virus neutralization ( vn ) assays of acute- and convalescent - phase ( 11 and 45 days after the acute - phase sample ) sera did not show evidence of seroconversion against the patient 's own isolate , a / ontario / rv1273/05 ( hi titer = 8 and vn titer = 16 on all 3 test dates ) . thus , although this farm worker had a febrile respiratory illness and no other etiologic agent was identified , we can not prove that he was actively infected with the triple reassortant virus ; he may have simply been harboring the virus in his nasal passages . nonetheless , this isolation shows that agricultural workers may be exposed to influenza viruses from livestock . in summary , this report describes the emergence and rapid spread since january 2005 of reassortant h3n2 influenza a viruses among pigs and turkeys across canada and isolation of a related virus from the nasal passages of a farm worker in ontario . the 4 swine isolates chosen for our analyses provide a sampling of viruses from british columbia to ontario , but clinical reports indicate that the outbreak of ili in pigs was much more extensive than this limited number of isolates might suggest . for example , h3n2 virus infections were confirmed on 22 swine farms in ontario between late april and early july 2005 . likewise , additional infections of turkeys with h3 viruses in 2005 were reported in british columbia ( on a farm that was near a swine farm where h3 virus was detected ) and in multiple flocks in manitoba ( a. hamel and g. nayar , pers . when this canadian epizootic is considered together with the extensive spread of genotypically similar h3n2 and h1n2 viruses in pigs and turkeys seen in the united states since 1998 , we see that viruses with this human / classical swine / avian triple reassortant genotype can efficiently infect both pigs and turkeys . the genbank numbers assigned to the gene sequences of viruses investigated in this study are as follows : a / ontario / rv1273/05 , dq469955dq469962 ; a / swine / alberta/14722/05 , dq469963dq469970 ; a / swine / british columbia/28103/05 , dq469971dq469978 ; a / swine / manitoba/12707/05 , dq469979dq469986 ; a / swine / ontario/33853/05 , dq469987dq469994 ; and a / turkey / ontario/31232/05 , dq469995dq470002 .