Persistence of Hong Kong influenza virus variants in pigs.

The A/Hong Kong/1/68 (H3N2) influenza virus which has not been isolated from man for several years, was recently isolated from pigs in Hong Kong. Influenza viruses similar to A/Victoria/3/75, which are currently circulating in man, were also isolated from pigs. Both above-mentioned viruses could be transmitted readily from pig to pig in experimental studies. The isolation of influenza viruses similar to A/Hong Kong/68 from pigs in 1976 suggests that pigs may serve as a potential reservoir for future human pandemics as well as a possible source of genetic information for recombination between human and porcine strains of influenza virus.

Electrophoretic comparison of the genomes of North American bluetongue viruses, one Australian bluetongue virus, and three other related orbiviruses.

The genomes of U.S. bluetongue viruses, an Australian bluetongue virus, and three other related orbiviruses were analyzed by polyacrylamide gel electrophoresis. The genomes were comprised of ten segments of double-stranded (ds) RNA. Estimates of the molecular weights of the dsRNA segments revealed that the U.S. bluetongue serotypes were remarkably similar. Although the dsRNA profiles of the viruses exhibited common segments, each virus had a distinct dsRNA profile. The usefulness of the genome analysis as a diagnostic tool for identification and for epidemiologic studies is discussed.

Detection and differentiation of strains of Newcastle Disease Virus by complement fixation.

A complement-fixation test to detect Newcastle disease virus with antiserum produced in guinea pigs is described. Methodology is given for serum production and for standardization of the test. The test was used to differentiate 13 strains of Newcastle disease virus. Velogenic strains, including isolants form 1970-71 disease outbreaks in California, Florida, and Texas, were poor complement-fixing antigens, whereas lentogenic strains, including LaSota, Hitchner, and England F, were strong complement-fixing antigens. Mesogenic strains ranged from weak to strong in complement-fixing capabilities. This test can be used to differentiate velogenic field isolants from vaccine strains such as LaSota, Hitchner, and Roakin.

Vaccination for fowl plague.

Influenza A/turkey/Oregon/71 virus has antigenic characteristics of fowl plague virus but is avirulent for chickens. The virus was inoculated intratracheally in chickens at several dosage levels and resulted in the formation of antibody and immunity against fowl plague. The avirulent virus replicated in chickens and was recoverable by tracheal swab specimens up to 4 days after inoculation. Although the virus was transmitted to contact controls at the time when their cagemates were inoculated, it was not transmitted to contact controls placed with chickens inoculated 24 hours earlier. After 10 passages in chickens, the virus remained avirulent for chickens and turkeys.

Diversity of influenza A virus subtypes isolated from domestic poultry in Hong Kong.

The second phase of a 2-year influenza virus surveillance programme of domestic avian species in Hong Kong (up to October 1977) yielded influenza A virus, Newcastle disease virus, and Hong Kong paramyxovirus, as well as unidentified haemagglutinating agents. These viruses were isolated from the trachea or cloaca of apparently healthy domestic ducks, geese, and chickens originating from China and Hong Kong. Twenty-five combinations of haemagglutinin and neuraminidase surface antigens were identified from the 136 influenza A viruses isolated. Eight of the combinations do not appear to have been previously reported - Hav3Nav2, Hav4Nav2, Hav4Nav4, Hav4Nav5, Hav4Neq1, Hav6Nav4, Hav6Nav6, and Hav9Nav1. The existence of such a diverse pool of influenza virus genetic information may play a role in the emergence of new human pandemic strains.

Identification of a swine influenza virus (Hsw1N1) isolated from a duck in Hong Kong.

An influenza A virus isolated from a duck during a recent surveillance study on commercial poultry from the People's Republic of China and the New Territories, Hong Kong, was shown to possess Hswl antigens related to that of the swine (Hsw1N1) influenza virus. The isolation of an Hsw1N1 influenza virus from ducks indicates that avian species, as well as pigs, may serve as a reservoir of this potential pathogen for humans. The virus was avirulent for ducks, turkeys, chickens, and pigs.

Isolation and characterization of influenza A viruses from avian species in Hong Kong.

Surveillance of apparently healthy ducks, chickens, and geese at a poultry dressing plant in Hong Kong yielded 51 haemagglutinating viruses 25 of which were influenza A viruses. Of these, 24 were subtyped into 13 combinations based on haemagglutinin and neuraminidase surface antigens. Of the 13 different influenza A viruses isolated, 7 possessed combinations of haemagglutinin and neuraminidase subunits that have not been reported previously-i.e., Hav2N1, Hav2Nav5, Hav4N2, Hav7N2, Hav7Nav1, Hav7Nav3, and Hav7Nav6. Four of the isolates were non-avid: they were not neutralized by antisera to any of the reference subtypes of influenza A viruses, yet antisera to each isolate inhibited both that virus and a known reference strain. The large number of combinations of haemagglutinin and neuraminidase and the isolation of two different influenza A viruses from one duck suggests that recombination may be occurring in nature.

Isolation and serological characterization of influenza A viruses from birds that were dead on arrival at Tokyo airport.

Twenty-two strains of influenza A virus isolated from caged birds which had been imported into Japan from India and Thailand and had died druing transportation to Tokyo. Serological tests divided these strains into two groups. Viruses in the first group contained Hav7 hemagglutinin and were related antigenically to A/duck/Ukraine/1/63 [Hav7 Neq2]; viruses in the second group contained Hav4 hemagglutining and were related to A/duck/Czech/56 [Hav 4 Nav 1]. All strains contained Neq2 neuraminidase that was closely related to that fo A/equine/Miami/1/63[Heq2 Neq2] and A/duck/Ukraine/1/63[Hav7 Neq2]. It was concluded that the strains in the first group were Hav7 Naq2 and those in the second group were Hav4 Neq2; both group of viruses showed antigenic drift from the prototype strains.