Haemagglutinin-inhibiting antibodies against swine influenza and Hong Kong influenza viruses in swine sera in the USA

Previous reports have established that swine in the midwestern states of the USA have a high incidence of classical swine influenza and that swine become infected with Hong Kong-like influenza viruses when these are prevalent in the human population. This investigation was undertaken to estimate, on the basis of 2245 sera collected randomly from swine going to slaughter in the USA during the summer months of 1974, how many of the animals had haemagglutination-inhibiting (HI) antibodies against swine influenza and Hong Kong influenza viruses. Based on HI titres of 20 or greater, our serological survey revealed that swine influenza virus infection was widespread throughout the USA, since 20.45% of the sera tested had positive HI titres. However, serological evidence of infection of swine with Hong Kong-like viruses was present in only 2.63% of the sera tested.     

Lack of evidence for human-to-human transmission of avian influenza A (H9N2) viruses in Hong Kong, China 1999

In April 1999, isolation of avian influenza A (H9N2) viruses from humans was confirmed for the first time. H9N2 viruses were isolated from nasopharyngeal aspirate specimens collected from two children who were hospitalized with uncomplicated, febrile, upper respiratory tract illnesses in Hong Kong during March 1999. Novel influenza viruses have the potential to initiate global pandemics if they are sufficiently transmissible among humans. We conducted four retrospective cohort studies of persons exposed to these two H9N2 patients to assess whether human-to-human transmission of avian H9N2 viruses had occurred. No serologic evidence of H9N2 infection was found in family members or health-care workers who had close contact with the H9N2-infected children, suggesting that these H9N2 viruses were not easily transmitted from person to person.     

Genetic and antigenic relatedness of H3 subtype influenza A viruses isolated from avian and mammalian species

In 2004, we isolated triple reassortant H3N2 influenza viruses from turkey breeder hens in Ohio and Illinois. The Illinois flock was vaccinated twice with an inactivated H3N2 vaccine containing a swine origin virus before the outbreak. Additionally, a commercial inactivated vaccine containing an H3N4 virus of duck origin is being used in some turkey breeders. This prompted us to initiate a comparative study on the antigenic and genetic relatedness of various H3 subtype influenza viruses isolated from turkeys, ducks, pigs and humans. The antigenic relatedness between the different viruses was evaluated with the Archetti and Horsfall formula, while nucleotide genetic similarities were calculated using pairwise alignments. Results obtained indicated a high degree of antigenic (>90%) and genetic (>99%) similarities among the turkey-origin H3N2 viruses. However, the turkey viruses were antigenically distantly related to the swine-origin vaccine virus (<30%), although they had approximately 95% genetic similarity in the HA1 gene. Additionally, major genetic and antigenic changes were observed between the turkey viruses and the H3N4 duck vaccine virus as well as the H3N2 human virus. Such genetic and antigenic differences between the turkey-origin viruses and other H3 subtype viruses including vaccine strains could be the reason for the failure in protection in the Illinois turkey breeders vaccinated with swine origin virus. This also emphasizes the importance of using viruses for vaccines that are antigenically similar to the field strains.     

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.     

Antigenic variation among avian influenza A viruses

A total of 16 strains of influenza A virus isolated in 1965-66 from quail, ducks, turkeys, pheasants and chickens bred in poultry farms situated in Pavia and surrounding districts in northern Italy were investigated from the point of view of antigenic grouping by the complement-fixation test.     

Avian influenza A viruses of southern China and Hong Kong: ecological aspects and implications for man

Continuous surveillance of the influenza viruses isolated from domestic poultry from southern China and Hong Kong over more than 4 years resulted in the isolation of influenza viruses possessing 46 different combinations of haemagglutinin (H) and neuraminidase (N) subtypes. Of these, 43 were obtained from ducks from China. In all cases, infection appeared to be asymptomatic. The antigenic combination found most commonly in the viruses isolated was H4N6, which accounted for approximately one-quarter of the duck isolates, its occurrence being more frequent than expected from a statistical analysis of the observed frequencies of the haemagglutinin and neuraminidase genes among all the isolates. Some combinations of H and N occurred less frequently than expected or not at all. Influenza viruses tended to be isolated more frequently from ducks during the summer months in comparison with paramyxoviruses, which were more commonly encountered in the winter. Possible reasons for the great antigenic diversity of influenza A viruses in the poultry, especially the ducks, in the region are discussed together with the potential significance of these viruses to the emergence of human influenza pandemics.     

Genomic signatures of human versus avian influenza A viruses

Position-specific entropy profiles created from scanning 306 human and 95 avian influenza A viral genomes showed that 228 of 4591 amino acid residues yielded significant differences between these 2 viruses. We subsequently used 15,785 protein sequences from the National Center for Biotechnology Information (NCBI) to assess the robustness of these signatures and obtained 52 "species-associated" positions. Specific mutations on those points may enable an avian influenza virus to become a human virus. Many of these signatures are found in NP, PA, and PB2 genes (viral ribonucleoproteins [RNPs]) and are mostly located in the functional domains related to RNP-RNP interactions that are important for viral replication. Upon inspecting 21 human-isolated avian influenza viral genomes from NCBI, we found 19 that exhibited > or =1 species-associated residue changes; 7 of them contained > or =2 substitutions. Histograms based on pairwise sequence comparison showed that NP disjointed most between human and avian influenza viruses, followed by PA and PB2.     

Serological evidence of Hantaan-related viruses in Hong Kong

Sera from rats (Rattus norvegicus), domestic animals and man in Hong Kong were studied by immunofluorescent antibody assay and plaque reduction neutralization tests for evidence of infection by Hantaan-related viruses. Antibody probably arising from infection by Seoul or a Seoul-like virus was detected in rat and human sera (and one pig serum), highlighting the potential public health importance of this group of viruses in Hong Kong, and in the region.     

Impact of severe acute respiratory syndrome and the perceived avian influenza epidemic on the increased rate of influenza vaccination among nurses in Hong Kong.

OBJECTIVE: To determine the rate of influenza vaccination and the factors associated with the vaccination's acceptance among nurses in Hong Kong. DESIGN: Cross-sectional survey. PARTICIPANTS: Nurses practicing between 2003 and 2007. METHODS: A questionnaire was sent to all nurses registered with any of the 3 nursing associations that participated in this study. RESULTS: A total of 941 completed questionnaires were available for analysis, though not all nurses responded to every question (response rate, 33.5%-36.3%). Vaccination rates in 2006 and 2007 were 57.2% and 46.2%, respectively. Nurses who were vaccinated in 2006 were more likely to get vaccinated in 2007 (P<.01); 56% of the nurses perceived influenza vaccine as being effective against influenza. The perceived effectiveness of influenza vaccine was a consistent predictor of rates of vaccination in 2006 (odds ratio [OR], 8.47 [95% confidence interval {CI}, 6.13-11.70]; P<.01) and 2007 (OR, 6.05 [95% CI, 3.79-9.67]; P<.01). Concern about contracting avian influenza was a predictor of the vaccination rate in 2006 but not in 2007 (OR, 1.47 [95% CI, 1.03-2.09]; P<.05), as was the perceived lack of control over avian influenza infection (OR, 1.52 [95% CI, 1.06-2.18]; P<.05). CONCLUSIONS: The overall influenza vaccination rate for nurses in Hong Kong was about 50%. It was affected by the perceived threat of an impending outbreak. The attitudes of nurses toward the effectiveness of and rationale for vaccination were a major barrier to increasing the rate of vaccination.