Biomedical subjects
Publications and source records attributed to R G Webster.
Two strains of influenza virus, A/wagtail/Ukraina/107/74 and A/dove/Ukraina/111/74, were isolated in virological studies of semisynanthropic species of birds shot near villages in the Rovno region (Western Ukraine). Both strains were found to be antigenically identical with influenza A/England/42/72 virus.
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Two procedures for characterising the genomes of recombinant influenza viruses are described. The first of these involves ribonuclease T4 oligonucleotide fingerpart analysis of separated viral RNAs labelled either in vivo or in vitro and the second utilises polyacrylamide gel electrophoresis to identify the double-stranded molecules formed by hybridisation between the complementary and virion RNAs of two viruses. Although the latter method is more suitable for routine screening purposes, both procedures are suitable for distinguishing between equivalent RNA components of closely related viruses.
Influenza subunit vaccines are poorly immunogenic in unprimed lower animals and man and a method was sought to potentiate the humoral response. Intact heterologous influenza A virus vaccine (A/Victoria/3/75 [H3N2]) potentiated the antibody response of hamsters to A/NJ/76 [Hsw1 N1] subunit vaccines but large doses of intact virus were required. Studies in seronegative young human adults showed that much lower doses of homologous A/NJ/76 [Hsw1 N1] virus potentiated the antibody response to both the hemagglutinin and neuraminidase subunits of A/NJ/76 influenza vaccines. This suggests that future influenza subunit vaccines for use in seronegative people should contain a small amount of whole virus vaccine, sufficient to potentiate the immune response to the subunits but insufficient to be reactogenic.
Studies on influenza viruses from feral ducks trapped in Canada in August 1976, gave a 26% isolation rate from cloacal samples of juvenile birds. Several different influenza A viruses were isolated, some of which possessed novel hemagglutinin and/or neuraminidase antigens. Influenza A viruses isolated from the rectum of feral ducks replicate in the upper respiratory tract and also in the intestinal tract of feral and domestic ducks. Representative human influenza viruses of the H0N1, H3N2 and Hsw1 N1 subtypes replicate in the upper respiratory tract of ducks but not in the intestinal tract. The A/Hong Kong/68 [H3N2] influenza virus that has not been isolated from man for several years was recently isolated from pigs originating from The People's Republic of China. A/Victoria/3/75-like influenza viruses that are currently circulating in man were also isolated from pigs. Both the A/Hong Kong/68 and the A/Victoria/75-like viruses transmitted readily from pig to pig in experimental studies. The susceptibility of ducks and pigs to infection with human influenza viruses suggests that these animals may play an important role in the ecology of influenza A viruses.
The pathogenicity potential of two H13N2 influenza viruses, one isolated from turkeys and the other isolated from surface water, was evaluated in turkeys, chickens, and mallard ducks (Anas platyrhynchos) after intracranial and oculonasal inoculation. Both isolates replicated in turkey poults, causing depressed weight gain, morbidity and mortality; both also caused histopathological lesions, such as mild to severe pancreatitis, hepatitis, and nephritis in turkeys. These isolates replicated in mallard ducklings but not in chickens. There was depressed weight gain in ducklings given the H13N2 isolate from water. Neither isolate caused morbidity or mortality in ducklings or chicks after inoculation.
The deduced amino acid sequence at the hemagglutinin (HA) cleavage site of 76 avian influenza (AI) viruses, subtypes H5 and H7, was determined by reverse transcription-polymerase chain reaction and cycle sequencing techniques to assess pathogenicity. Eighteen of the 76 viruses were isolated in 1993 and 1994 from various sources in the United States. In addition, 34 H5 (4 highly pathogenic [HP] and 30 non-highly pathogenic [non-HP]) and 24 H7 (3 HP and 21 non-HP) repository viruses, isolated between 1927 and 1992, were sequenced and the sequences compared to those in recent isolates. All repository HP H5 and H7 viruses studied had multiple basic amino acids adjacent to the HA cleavage site and most had basic amino acids in excess of the proposed minimum motif B-X-B-R (B = basic amino acids arginine or lysine, X = nonbasic amino acid, R = arginine) that has been associated with high pathogenicity. Of the non-HP viruses studied, 35 of 38 for H5 and 30 of 31 for H7 conformed to the motif B-X-X-R and B-X-R, respectively. Two non-HP H5 viruses had the motif X-X-X-R at the cleavage site and a third had the motif B-X-X-K (K = basic amino acid lysine). One non-HP H7 (A/Pekin robin/CA/30412-5/94) had four basic amino acids (K-R-R-R) adjacent to the cleavage site. Although the Pekin robin isolate did not produce disease in chickens under the conditions of the study it did have the amino acid sequence compatible with that in HP AI viruses and, therefore, is considered potentially HP. This is the first account of an H7 virus that is non-HP in chickens but meets the molecular criterion to be classified as HP.
The presence of highly pathogenic H5N2 avian influenza in domestic poultry in Mexico that is not being eradicated by conventional depopulation methods constitutes an imminent problem for poultry producers and agricultural authorities in the United States. The present report considers the candidate vaccines available to H5N2 influenza virus and establishes that a fowl pox-H5 recombinant can provide protection from lethal Mexican H5N2, and prevent shedding in the feces and transmission to contact birds. Inactivated and recombinant vaccines may be useful adjuncts to eradication if the H5N2 influenza virus spreads to the United States or the countries in Central America.
The control and eventual eradication of H5N2 influenza virus from domestic poultry in Mexico is dependent on the use of avian influenza (AI) vaccine strategies. This study was performed to determine the amount of hemagglutinin (HA) antigen required to control the signs of disease from a highly pathogenic H5N2 influenza virus (A/Chicken/ Queretaro/19/95) and the amount of antigen required to prevent shedding of virus from vaccinated birds. Six commercial inactivated water in oil H5N2 vaccines available in Mexico were compared with standardized vaccines to assess their efficacy. The amount of HA required to prevent the signs of disease from A/Chicken/Queretaro/19/95 influenza virus was approximately 0.4 microgram per dose. Each of the six commercially available vaccines prevented disease signs, and half of the vaccines significantly reduced viral shedding from vaccinated birds. There is a need for standardization of AI virus vaccine, and the antigen content should be increased in some of the commercially available AI vaccines in Mexico.