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At least 19 recordsLinked to original sources
PubMed1995

Differentiation of cognate dsRNA genome segments of bluetongue virus reassortants by temperature gradient gel electrophoresis.

The analysis of reassortant viruses has been a valuable tool in the investigation of protein interaction and function in double-stranded (ds) RNA virus research. The differentiation of cognate dsRNA genome segments of reassortants is conventionally achieved by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). However, due to a high degree of sequence homology among different bluetongue virus (BTV) serotypes, it is not uncommon to find that certain cognate dsRNA segments cannot be differentiated by SDS-PAGE. Temperature gradient gel electrophoresis (TGGE) has been shown to be a much more sensitive method of differentiating RNA or DNA fragments of high sequence homology. Here we report the preliminary application of TGGE in analysis of genomic reassortants of two BTV serotypes, 1 and 23. While six out of ten genome segments between BTV-1 and BTV-23 could not be resolved by SDS-PAGE, all of them were differentiated by TGGE. The ability of TGGE to distinguish between dsRNA segments of high sequence homology may also make it useful in the search for BTV genes responsible for defined characteristics, such as virulence, by differentiating wild-type and mutated gene segments of viruses displaying altered phenotypes.

Bluetongue virus↗
PubMed2004

Genetic diversity of influenza B virus: the frequent reassortment and cocirculation of the genetically distinct reassortant viruses in a community.

To characterize the genetic diversity of influenza B viruses isolated during one influenza season, the antigenic and genetic relationships among 20 strains of influenza B virus isolated in February and March 2001 at one pediatric clinic in Yamagata City, Japan, were investigated. The HA gene and seven other gene segments were phylogenetically divided into three distinct sublineages (Harbin/7/94-, Tokyo/6/98-, and Shiga/T30/98-related lineage) of the Yamagata/16/88-like lineage. The NS genes of the viruses belonging to the Harbin/7/94-related lineage have additional three nucleotides at positions 439-447, and were phylogenetically distinguishable from those of the currently circulating Yamagata/16/88- and Victoria/2/87-like lineages, but were closely related to that of the Yamagata/16/88-like lineage isolated before 1994. Moreover, four strains of influenza B virus isolated in the same community between 2002 and 2003 were further examined. Phylogenetic analysis revealed that a virus of Victoria/2/87-like lineage isolated in 2003 had acquired the NA, NS, M, and PA gene segments from a Shiga/T30/98-like virus, and two strains of Harbin/7/94-related lineage had acquired the various gene segments from Shiga/T30/98-like virus through a reassortment event. These results indicate that genetically distinct multiple viruses can combine to cause an influenza B epidemic in a community and that the frequent reassortment among these viruses plays a role in generating the genetic diversity of influenza B viruses.

Adolescent↗
PubMed1987

The avian influenza virus nucleoprotein gene and a specific constellation of avian and human virus polymerase genes each specify attenuation of avian-human influenza A/Pintail/79 reassortant viruses for monkeys.

Reassortant viruses which possessed the hemagglutinin and neuraminidase genes of wild-type human influenza A viruses and the remaining six RNA segments (internal genes) of the avian A/Pintail/Alberta/119/79 (H4N6) virus were previously found to be attenuated in humans. To study the genetic basis of this attenuation, we isolated influenza A/Pintail/79 X A/Washington/897/80 reassortant viruses which contained human influenza virus H3N2 surface glycoprotein genes and various combinations of avian or human influenza virus internal genes. Twenty-four reassortant viruses were isolated and first evaluated for infectivity in avian (primary chick kidney [PCK]) and mammalian (Madin-Darby canine kidney [MDCK]) tissue culture lines. Reassortant viruses with two specific constellations of viral polymerase genes exhibited a significant host range restriction of replication in mammalian (MDCK) tissue culture compared with that in avian (PCK) tissue culture. The viral polymerase genotype PB2-avian (A) virus, PB1-A virus, and PA-human (H) virus was associated with a 900-fold restriction, while the viral polymerase genotype PB2-H, PB1-A, and PA-H was associated with an 80,000-fold restriction of replication in MDCK compared with that in PCK. Fifteen reassortant viruses were subsequently evaluated for their level of replication in the respiratory tract of squirrel monkeys, and two genetic determinants of attenuation were identified. First, reassortant viruses which possessed the avian influenza virus nucleoprotein gene were as restricted in replication as a virus which possessed all six internal genes of the avian influenza A virus parent, indicating that the nucleoprotein gene is the major determinant of attenuation of avian-human A/Pintail/79 reassortant viruses for monkeys. Second, reassortant viruses which possessed the viral polymerase gene constellation of PB2-H, PB1-A, and PA-H, which was associated with the greater degree of host range restriction in vitro, were highly restricted in replication in monkeys. Since the avian-human influenza reassortant viruses which expressed either mode of attenuation in monkeys replicated to high titer in eggs and in PCK tissue culture, their failure to replicate efficiently in the respiratory epithelium of primates must be due to the failure of viral factors to interact with primate host cell factors. The implications of these findings for the development of live-virus vaccines and for the evolution of influenza A viruses in nature are discussed.

Animals↗
PubMed1982

Evaluation of a phenotypic revertant of the A/Alaska/77-ts-1A2 reassortant virus in hamsters and in seronegative adult volunteers: further evidence that the temperature-sensitive phenotype is responsible for attenuation of ts-1A2 reassortant viruses.

In a previous study, a seronegative child to whom attenuated A/Alaska/77-ts-1A2 virus was administered (37 degrees C shutoff temperature for plaque formation) shed virus with an altered temperature-sensitive (ts) phenotype (40 degrees C shutoff temperature) (Murphy et al., Ann. N.Y. Acad. Sci. 354:172-182, 1980; Tolpin et al., Virology 112:505-517, 1981). This ts+ virus (FV1319) was evaluated for its level of replication in hamsters and for its virulence for humans. In hamsters, FV1319 ts+ virus replicated to the same level in the nasal turbinates as that of which the A/Alaska/77 wild-type virus replicated, but its replication in the lungs was reduced 40-fold. In contrast, the A/Alaska/77-ts-1A2 reassortant achieved a titer in hamster nasal turbinates that was significantly lower (P less than 0.005) than those achieved by the wild-type and the FV1319 viruses; the A/Alaska/77-ts-1A2 reassortant was not recoverable from the lungs. In seronegative adult volunteers, the pattern of replication of the FV1319 virus was similar to that of the A/Alaska/77 wild-type virus. The illness induced by the FV1319 ts+ virus was also similar to that caused by the wild-type virus. In contrast, the A/Alaska/77-ts-1A2 reassortant was satisfactorily attenuated in adult volunteers. These results suggest that attenuation of the A/Alaska/77-ts-1A2 reassortant virus in humans is a function of the ts phenotype: loss of this phenotype restored virulence. The ability of the A/Alaska/77-ts-1A2 reassortant to lose its ts phenotype and regain virulence during growth in a permissive host limits the usefulness of the ts-1A2 reassortants as vaccine viruses for humans.

Animals↗
PubMed2005

Simple and rapid strategy for genetic characterization of influenza B virus reassortants.

Genetic reassortment of influenza viruses is widely used for creating viruses with specific phenotypes. Reassortment of two influenza viruses, each with eight RNA segments potentially yields as many as 256 gene segment combinations. Therefore, confirmation that progeny viruses possess genomes corresponding to the specified phenotypes can be laborious and time-consuming. To establish a convenient method for genotyping influenza virus reassortants, we adapted single-strand conformation polymorphism analysis (SSCP) using standard laboratory equipment. By varying the concentration of polyacrylamide between 4-6% and the concentration of glycerol between 5-8% in the gel, together with adding PCR primers to the DNA sample during the denaturing step, optimal conditions can be found for SSCP with little effort. The described method has high accuracy and reliability, and provides a tool for rapid, cost-effective genetic screening and assessment of the purity and genetic stability of the reassortant viruses. This method should be useful in basic research applications and in preparing reassortant viruses for vaccine use.

Base Composition↗
PubMed1995

Are there alternative avian influenza viruses for generation of stable attenuated avian-human influenza A reassortant viruses?

The present study evaluated gull influenza A viruses as donors of attenuating genes for the production of live, attenuated influenza A H1N1 and H3N2 avian-human (ah) reassortant viruses for use as vaccines to prevent disease due to influenza A viruses in humans. The previously evaluated duck influenza A viruses were abandoned as donors of attenuating avian influenza virus genes because clinical evaluation of H1N1 and H3N2 ah reassortant virus vaccines derived from duck viruses documented residual virulence of H1N1 reassortants for seronegative infants and young children. Gull influenza A viruses occupy an independent ecologic niche and are rarely isolated from species other than gulls. The possibility of using gull influenza A viruses as donors of internal gene segments in ah reassortant viruses was evaluated in the present study using three different gull viruses and three human influenza A viruses. Gull-human H3N2 reassortant influenza A viruses with the desired 6-2 genotype (six internal avian influenza virus genes and the two human influenza virus surface glycoprotein genes) were readily generated and were found to be attenuated for squirrel monkeys and chimpanzees. However, ah reassortant viruses with gull and human influenza A H1N1 genes were difficult to generate, and reassortants that had the desired genotype of six gull virus genes with human influenza A H1 and N1 genes were not isolated despite repeated attempts. The gull PB2, NP and NS genes were not present in any of the gull-human H1N1 reassortants generated. The under-representation of these three gene segments suggests that reassortants bearing one or more of these three gene segments might have reduced viability indicative of a functional incompatibility in their gene products. The difficulties encountered in the generation of a 6-2 gull-human H1N1 reassortant virus are sufficient to conclude that the gull influenza A viruses tested would not be useful as donors of sets of six internal genes to attenuate human influenza A viruses. This study also identifies influenza virus gene segments that appear to be incompatible for generation of reassortants. Elucidation of the molecular basis of this restriction may provide information on intergenic interactions involved in virion assembly or packaging.

Animals↗
PubMed1986

Comparison by studies in squirrel monkeys, chimpanzees, and adult humans of avian-human influenza A virus reassortants derived from different avian influenza virus donors.

We evaluated the abilities of three different avian influenza A viruses to attenuate the wild-type human influenza A/Korea/1/82 (H3N2) virus in squirrel monkeys, chimpanzees, and adult seronegative human volunteers. Two of these, avian influenza A/Mallard/NY/78 and A/Mallard/Alberta/76 viruses, appeared to be satisfactory donors of attenuating genes for the production of live influenza A reassortant virus vaccines for human use because the reassortants exhibited an acceptable balance between attenuation and immunogenicity.

Animals↗
PubMed1992

The attenuation phenotype conferred by the M gene of the influenza A/Ann Arbor/6/60 cold-adapted virus (H2N2) on the A/Korea/82 (H3N2) reassortant virus results from a gene constellation effect.

A single gene reassortant (SGR) virus that derived its M gene from the attenuated influenza A/Ann Arbor/6/60 cold-adapted (CA) donor virus and the remaining genes from the A/Korea/82 (H3N2) wild type (WT) virus (designated A/Korea/82 CA M-SGR) was previously shown to be attenuated in mice, hamsters, ferrets, and humans. The attenuation (ATT) phenotype of this SGR virus could result directly from an altered function of the mutant M gene product of the A/Ann Arbor/6/60 CA virus, which differs from the M gene of the A/Ann Arbor/6/60 WT virus at only one amino acid or, indirectly from a gene constellation effect in which ATT results from an inefficient interaction between the products of the M gene of the A/Ann Arbor/6/60 virus and other genes of the A/Korea/82 virus. Several lines of evidence from the present study are consistent with our interpretation that the ATT phenotype of the A/Korea/82 CA M-SGR results from a gene constellation effect. First, the A/Korea/82 CA M-SGR and an A/Korea/82 SGR containing the A/Ann Arbor/6/60 WT M gene were each restricted in replication in the upper and lower respiratory tract of mice compared with the A/Korea/82 WT virus. Second, an A/Udorn/72 CA M-SGR containing the M gene from the A/Ann Arbor/6/60 CA donor virus in a background of other genes derived from the A/Udorn/72 (H3N2) WT virus was not attenuated in the respiratory tract of mice. These data suggest that the change in the amino acid sequence of the M gene product from the A/Ann Arbor/6/60 WT to CA virus is not responsible for the ATT phenotype of the A/Korea/82 CA M-SGR. In addition, evidence of the genetic instability of the A/Korea/82 CA M-SGR is presented, specifically, an extragenic mutation that results in loss of the ATT phenotype. The implications of these findings for the ATT phenotype of the live attenuated reassortant viruses derived from the A/Ann Arbor/6/60 CA donor virus are discussed.

Adaptation, Physiological↗
PubMed1982

Reassortant virus derived from avian and human influenza A viruses is attenuated and immunogenic in monkeys.

An influenza A reassortant virus that contained the hemagglutinin and neuraminidase genes of a virulent human virus, A/Udorn/72 (H3N2), and the six other influenza A virus genome segments from an avirulent avian virus, A/Mallard/New York/6750/78 (H2N2), was evaluated for its level of replication is squirrel monkeys and hamsters. In monkeys, the reassortant virus was as attenuated and as restricted in its level of replication in the upper and lower respiratory tract as its avian influenza virus parent. Nonetheless, infection with the reassortant induced significant resistant to challenge with virulent human influenza virus. In hamsters, the reassortant virus replicated to a level intermediate between that of its parents. These findings suggest that the nonsurface antigen genes of the avian parental virus are the primary determinants of restriction of replication of the reassortant virus in monkeys. Attenuation of the reassortant virus for primates is achieved by inefficient functioning of the avian influenza genes in primate cells, while antigenic specificity of the human influenza virus is provided by the neuraminidase and hemagglutinin genes derived from the human virus. This approach could lead to the development of a live influenza A virus vaccine that is attenuated for man if the avian influenza genes are similarly restricted in human cells.

Animals↗
PubMed2006

Molecular characterization of a reassortant virus derived from Lassa and Mopeia viruses.

In this article we describe two new complete genomic sequences of Old World Arenaviruses: the Mopeia (MOP) virus and the reassortant MOP/LAS virus, clone 29, or ML29. This reassortant has the large (L) RNA from MOP virus and the small (S) RNA from Lassa (LAS) virus, Josiah strain. Recent studies showed that the ML29 virus is not pathogenic for mice, guinea pigs, or macaques, can completely protect guinea pigs from Lassa virus, and elicit vigorous cell-mediated immunity in immunized monkeys (Lukashevich, I. S., Patterson, J., Carrion, R., Moshkoff, D., Ticer, A., Zapata, J., Brasky, K., Geiger, R., Hubbard, G. B., Bryant, J., and Salvato, M. S., J Virol 79, 13934-13942, 2005). This is a molecular characterization of a reassortant virus, which has been put forward as a live attenuated vaccine candidate against Lassa Fever. Sequence analysis of this reassortant virus revealed 5 non-conservative amino acid substitutions that distinguished it from the parental LAS and MOP viruses. Three substitutions were found outside the conserved RNA-dependent RNA polymerase (RdRp) motifs. A fourth substitution was located between the glycoprotein (GPC)-cleavage site and the putative fusion peptide of GP2. The nucleocapsid protein (NP) contained a fifth substitution in the carboxyl-terminal region of the protein. Two mutations were found within each non-coding terminus of the L segment and one mutation was located in the 3' non-coding region of the S segment of the MOP/LAS virus. ML29 mutations in its genomic termini may have implications for the genetic stability and replication efficiency of ML29 reassortant.

Amino Acid Sequence↗
PubMed1990

Use of reassortant viruses to map attenuating and temperature-sensitive mutations of the Rift Valley fever virus MP-12 vaccine.

A live-attenuated vaccine for Rift Valley fever virus (RVFV), MP-12, has been developed recently by undirected, serial mutagenesis of a RVFV strain (ZH548) isolated during the 1977 epidemic in Egypt. In the present study, the mutations responsible for attenuation of this virus have been examined by analysis of reassortant viruses generated between the vaccine strain and a wild RVFV strain isolated in Senegal. Reassortant viruses were generated efficiently in multiply infected Vero cells, and were readily isolated without application of selective pressures. The origin of the S and M genomic RNA segments in each cloned reassortant virus was determined with monoclonal antibodies capable of differentiating the nucleocapsid protein (S segment marker) or G1 glycoprotein (M segment marker) of the parental strains. The L segment of the vaccine strain was found to contain a temperature-sensitive (ts) mutation, and the origin of the L segment in most reassortants could be inferred by analysis of their ts phenotype. Analysis of the virulence properties of selected reassortant viruses in mice demonstrated that virulence characteristics were under polygenic control, and that at least one mutation capable of independently attenuating the virus existed on each genome segment. The L and M RNA segments were also found to contain ts mutations. These findings suggest that reversion to virulence is unlikely, and further indicate that genetic reassortment with wild-type viruses during a vaccination programme in endemic areas would also be expected to yield attenuated variants.

Animals↗
PubMed2004

Binding of influenza viruses to sialic acids: reassortant viruses with A/NWS/33 hemagglutinin bind to alpha2,8-linked sialic acid.

We have examined the specificity of binding of A/NWS/33 hemagglutinin (HA), exploring the effects of fucosylation, changing the Gal-GlcNAc linkage between the second and third sugars, and binding affinity for alpha2,8-linked sialic acid. The HA of A/NWS/33(HA)-Tokyo/67(NA) (NWS-Tok, H1N2) virus binds to 3'-linked sialyllactose with 10-fold higher affinity than 3' sialyllactosamine and 3-fold higher affinity than 6' sialyllactosamine. The P227H mutation in A/NWS/33(P227H)(HA)-A/Memphis/31/98(NA) (NWS-Mem/98, H1N2) results in sevenfold lower affinity for 3' sialyllactose, but binding to 6' sialyllactosamine is unchanged. The apparent switch from 3' to 6' specificity is solely due to a loss of Siaalpha2,3 binding. Fucosylation of the third sugar and changing the linkage between second and third sugars had little effect on binding by NWS-Tok, but marked effects on A/NWS/33(P227H)(HA)-tern/Australia/G70c/75(NA) (NWS-G70c, H1N9) and NWS-Mem/98. NWS-Tok, NWS-G70c, and NWS-Mem/98 bind to alpha2,8-bisialic acid with high affinity. NWS-Mem/98 can also bind to alpha2,8-trisialic acid, but with lower affinity. Together, these data show that alpha2,8-linked sialic acid, fucosylation of the third sugar, and linkage between the second and third sugars could play important roles in allowing efficient virus binding to its host cell. The finding that influenza viruses have the potential to bind to alpha2,8-linked sialic acid is a new influenza virus-receptor interaction pathway.

Animals↗
PubMedDate not supplied

An influenza A live attenuated reassortant virus possessing three temperature-sensitive mutations in the PB2 polymerase gene rapidly loses temperature sensitivity following replication in hamsters.

The purpose of the present study was to produce an influenza A H2N2 donor virus from which an attenuating PB2 gene bearing three discrete temperature sensitive (ts) mutations could be readily transferred to currently epidemic influenza A H1N1 and H3N2 viruses via genetic reassortment. An influenza A transfectant virus was first produced that contained site-directed ts mutations at amino acids 112, 265, and 556 in the PB2 gene of influenza A/AA/60 virus origin in a background of the other seven RNA segments from the influenza A/LA/87 (H3N2) virus. The A/LA/87 PB2 ts transfectant virus (clone 22B1) was mated with the A/AA/60 (H2N2) wild type virus, and six H2N2 ts reassortants were obtained. One reassortant virus, clone 25A1, possessed the triple ts PB2 gene in the context of all seven other genes of homologous A/AA/60 origin. Isolation of this reassortant permitted an examination of the contribution of the ts mutations present in a triple ts PB2 transfectant virus to its attenuation and phenotypic stability independent from an effect of the A/AA/60-A/LA/87 gene constellation on attenuation. It was found that the A/AA/60 triple ts reassortant virus was less ts, less attenuated, and less phenotypically stable than the A/LA/87 triple ts transfectant virus from which it was derived. The A/AA/60 reassortant possessing the PB2 gene containing three introduced ts mutations underwent rapid and significant loss of its temperature sensitivity following replication in the lungs of immunocompetent hamsters. This indicated that the A/AA/60-A/LA/87 gene constellation contributed significantly to the overall level of temperature-sensitivity, attenuation, and stability of the A/LA/87 triple ts transfectant virus. It is likely that the instability of the ts phenotype exhibited by the A/AA/60 triple ts reassortant virus would not be acceptable for a vaccine to be used in humans. The implications of these findings for the usefulness of ts mutations as the sole attenuating mutation in influenza virus vaccines is discussed.

Animals↗
PubMed1993

Influenza A virus reassortants with surface glycoprotein genes of the avian parent viruses: effects of HA and NA gene combinations on virus aggregation.

A series of 33 human-avian and human-mammalian influenza virus reassortant clones possessing either HA or both HA and NA genes of the avian or mammalian virus was obtained by crosses of A/USSR/90/77 (H1N1) human virus with 5 avian and 1 mammalian influenza virus strains. All of the reassortants possessing NA genes of the H1N1 human parent virus and HA gene of an avian or mammalian parent virus had high values of infectivity/HA activity ratio. Since this feature could result from a limited virion aggregation, several reassortants were analyzed by velocity sucrose gradient centrifugation. In all cases tested, the reassortants of H3N1, H4N1, H10N1 and H13N1 composition were shown to be aggregated, whereas the preparations of the parent H1N1 virus and the reassortants possessing both HA and NA genes from the avian parents were represented mostly by single virions. The aggregates were formed at 4 degrees C and dissociated at 37 degrees C. The dissociation was blocked by an inhibitor of neuraminidase activity (2-deoxy-2,3-dehydro-N-acetyl-neuraminic acid). The dissociation was reversible since the virions reaggregated at 4 degrees C; however, treatment with bacterial neuraminidase led to an irreversible dissociation of the aggregates. The tendency of the reassortants to aggregate correlates with an increased infectivity/HA ratio. No regular decrease in the neuraminidase activity in the virions of reassortants as compared to the parent H1N1 virus was revealed. The most likely explanation of the observed phenomenon seems to be an inefficient removal of sialic acid residues from the avian virus hemagglutinin by the human virus N1 neuraminidase.

Animals↗
PubMed1989

Comparison of the virologic and immunologic responses of volunteers to live avian-human influenza A H3N2 reassortant virus vaccines derived from two different avian influenza virus donors.

We compared the abilities of the six internal RNA segments of two avian influenza viruses, A/Mallard/Alberta/88/76 (H3N8) and A/Mallard/NY/6750/78 (H2N2), to confer attenuation on wild-type human influenza A/Bethesda/1/85 (H3N2) virus in seronegative adult volunteers. Live avian-human influenza A reassortant virus vaccines derived from either avian virus parent were comparable in the following properties: safety, infectivity, immunogenicity, and genetic stability. Since the avian influenza A/Mallard/Alberta/76 virus offered no clear advantage as a donor virus, we will conduct our future evaluations on live influenza A virus reassortants derived from the more extensively characterized avian influenza A/Mallard/NY/78 virus.

Animals↗
PubMed2004

Ngari virus is a Bunyamwera virus reassortant that can be associated with large outbreaks of hemorrhagic fever in Africa.

Two isolates of a virus of the genus Orthobunyavirus (family Bunyaviridae) were obtained from hemorrhagic fever cases during a large disease outbreak in East Africa in 1997 and 1998. Sequence analysis of regions of the three genomic RNA segments of the virus (provisionally referred to as Garissa virus) suggested that it was a genetic reassortant virus with S and L segments derived from Bunyamwera virus but an M segment from an unidentified virus of the genus Orthobunyavirus. While high genetic diversity (52%) was revealed by analysis of virus M segment nucleotide sequences obtained from 21 members of the genus Orthobunyavirus, the Garissa and Ngari virus M segments were almost identical. Surprisingly, the Ngari virus L and S segments showed high sequence identity with those of Bunyamwera virus, showing that Garissa virus is an isolate of Ngari virus, which in turn is a Bunyamwera virus reassortant. Ngari virus should be considered when investigating hemorrhagic fever outbreaks throughout sub-Saharan Africa.

Africa South of the Sahara↗
PubMed2000

Genetic characterization of H3N2 influenza viruses isolated from pigs in North America, 1977-1999: evidence for wholly human and reassortant virus genotypes.

Since 1998, H3N2 viruses have caused epizootics of respiratory disease in pigs throughout the major swine production regions of the U.S. These outbreaks are remarkable because swine influenza in North America had previously been caused almost exclusively by H1N1 viruses. We sequenced the full-length protein coding regions of all eight RNA segments from four H3N2 viruses that we isolated from pigs in the Midwestern U.S. between March 1998 and March 1999, as well as from H3N2 viruses recovered from a piglet in Canada in January 1997 and from a pig in Colorado in 1977. Phylogenetic analyses demonstrated that the 1977 Colorado and 1997 Ontario isolates are wholly human influenza viruses. However, the viruses isolated since 1998 from pigs in the Midwestern U.S. are reassortant viruses containing hemagglutinin, neuraminidase and PB1 polymerase genes from human influenza viruses, matrix, non-structural and nucleoprotein genes from classical swine viruses, and PA and PB2 polymerase genes from avian viruses. The HA proteins of the Midwestern reassortant swine viruses can be differentiated from those of the 1995 lineage of human H3 viruses by 12 amino acid mutations in HA1. In contrast, the Sw/ONT/97 virus, which did not spread from pig-to-pig, lacks 11 of these changes.

Animals↗
PubMed1986

Studies on the temperature sensitivity of influenza A virus reassortants nonpathogenic for chicken.

Influenza A virus reassortants which are nonpathogenic for chickens are like mammalian influenza A viruses in that they are temperature sensitive for growth at 41 degrees C. We have investigated the mechanism of this temperature sensitivity using reassortants between the two highly pathogenic strains A/FPV/Rostock/34 (FPV, H7N1) and A/turkey/England/63 (TE, H7N3). These reassortants show a strict correlation between the pathogenicity for chickens and the constellation of the genes coding for the ribonucleoprotein complex, RNP. Evidence is presented which shows that all viral components are synthesized in sufficient amounts and that the block in the viral replication cycle at the nonpermissive temperature is a late one affecting virus maturation. It is suggested that the RNP, although still enzymatically functional, may lose its ability to interact normally with viral surface components, thus interfering with the process of virus maturation. Some of the nonpathogenic reassortants which possessed the neuraminidase of TE showed an interesting temperature-dependent phenomenon: the haemagglutinin synthesized at the elevated temperature could only agglutinate erythrocytes at 20 degrees C, when the neuraminidase was inhibited or the infected cells vigorously disrupted by ultrasonication. This phenomenon is possibly not directly related to the temperature-sensitive block.

Animals↗