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The ecology of influenza viruses: a WHO memorandum
Abstract:
Influenza A viruses continue to be isolated from man, pigs, horses, and a wide range of avian species, especially ducks. The recent isolation of an influenza A virus from seals has added an additional mammal to the list of natural hosts for these viruses. In contrast, influenza B viruses have been isolated only from man.The haemagglutinin of a virus isolated from gulls in the United States of America could not be identified with reference antisera and may constitute a new haemagglutinin subtype.Studies in swine suggest that H1N1 viruses related to A/New Jersey/8/76 continue to circulate in some countries of the world, and that the H3N2 and H1N1 viruses can be transmitted from man to pigs. The isolation from pigs of an H1N1 virus that is antigenically similar to avian H1N1 isolates and the isolation of "classical" swine influenza virus from a piglet in Czechoslovakia are of particular interest and raise the question of the source of the viruses.Preliminary studies on equine influenza viruses (H3N8) (Heq2Neq2) from horses in Europe suggest that significant antigenic drift has occurred in viruses of this subtype since the prototype was identified in 1963.The role of influenza viruses from lower animals and birds in the genesis of new human strains is unknown, and the genes responsible for host range and virulence have not yet been identified. The availability of techniques for analysis of all the RNAs and the gene products will permit further studies on these important questions.
Insights
Influenza A viruses infect various species, including birds, pigs, and seals. Research is exploring the origins of novel influenza strains and their potential to impact human health.
Area of Science:
- Virology
- Infectious Diseases
- Public Health
Background:
- Influenza A viruses are widespread in avian and mammalian populations, with influenza B viruses primarily affecting humans.
- Recent isolations of influenza A from seals and gulls highlight the diverse host range and potential for novel subtypes.
- Swine influenza studies indicate ongoing circulation of H1N1 and H3N2 strains, with evidence of human-to-pig transmission.
Purpose of the Study:
- To investigate the natural hosts and potential for novel subtypes of influenza A viruses.
- To understand the transmission dynamics of influenza viruses between humans and swine.
- To explore the origins and genetic evolution of equine influenza viruses.
Main Methods:
- Virus isolation and identification from various animal species.
- Antigenic characterization using reference antisera.
- Analysis of viral RNA and gene products for further studies.
Main Results:
- Influenza A viruses isolated from a wide range of animals, including seals, expanding the known host range.
- Identification of a potential new haemagglutinin subtype from gulls.
- Evidence of human-to-swine transmission of H1N1 and H3N2 influenza viruses.
- Antigenic drift observed in equine influenza H3N8 viruses since 1963.
Conclusions:
- The broad host range of influenza A viruses, including avian, swine, and marine mammals, poses continuous surveillance challenges.
- The emergence of novel influenza subtypes and reassortment events in animal reservoirs remain a significant concern for public health.
- Further research into viral genetics and host-pathogen interactions is crucial for predicting and preventing future influenza pandemics.