Although these mutations may not be systematically removed through purifying, or negative, selection, they also do not become fixed within the population [ 29 ]. However, computational models show that deleterious mutations can impact the overall evolutionary trajectory of influenza by restricting the rate of antigenic change of the virus [ 30 , 31 ]. A recent study on H3N2 found that cooperation could clearly occur between 2 different H3N2 variants. With 1 variant excelling in cell entry and the other excelling in cell exit, the viral population had a higher replicative success when the 2 variants were mixed than when they were separate [ 32 ].
Natural world a reservoir for human disease
Similar results were found when looking at the expression of influenza proteins. Although individual virions that lack a fundamental protein may appear noninfectious, when they are part of a viral population, they can contribute by complementation-dependent protein expression to increase the fitness of the population as a whole [ 33 ]. While cooperation is associated with the division of labor between variants in the above example, between cellular entry and exit , competition occurs when multiple members of a population independently develop beneficial mutations. This scenario, amongst other things, can create an arms race between members of the population.
Thus, the intrinsic diversity and loose transmission bottlenecks in circulating influenza populations can facilitate an increase in pathogenesis by allowing viral variants to cooperate with one another or by increasing the number of beneficial mutations appearing in cocirculating clones. Clearly, influenza evolution is a multilayered process, and much work needs to be done to fully capture its richness. Such work requires mathematical tools and next-generation sequencing technologies to operate in concert to capture the full breadth of influenza transmission.
Effective vaccination strategies would require a better understanding of the complex interplay of multivariant transmission dynamics, inter- and intrahost viral evolution, and the interaction of diverse strains with the host immune system. How does flu evolve? By making mistakes and reshuffling genes The 2 main influenza types that infect humans, A and B, are part of the Orthomyxoviridae family, which is characterized by segmented negative-sense RNA genomes.
Genomic surveillance of avian-origin influenza A viruses causing human disease
Download: PPT. Who gets the flu? Influenza has a wide host range Humans are not the only animals to get influenza infections. What gets around? Types, subtypes, and strains of flu cocirculate Recently, the interplay between influenza transmission and evolution has been of particular interest in characterizing interspecies transmission, expansion of host range, and the diversity of viruses circulating. A swarm of viruses Because of the error-prone RNA polymerase, influenza populations exist as a mixture of genetically diverse viral particles.
How much worse than 1 virus are 2 viruses? They can be more than twice as bad A recent study on H3N2 found that cooperation could clearly occur between 2 different H3N2 variants. References 1. Byerly CR. The U. Public Health Rep. Global patterns of influenza a virus in wild birds. J Clin Virol. Lauring AS, Andino R. Quasispecies theory and the behavior of RNA viruses. PLoS Pathog. Avian-to-human transmission of the PB1 gene of influenza A viruses in the and pandemics.
Frontiers | Influenza A Virus Cell Entry, Replication, Virion Assembly and Movement | Immunology
Journal of virology. Nonrandom association of parental genes in influenza A virus recombinants. Viral reassortment as an information exchange between viral segments. Proceedings of the National Academy of Sciences. However, cross-protection was limited between viruses with a different HA subtype.
Collectively, the activities of the FLUPIG study provided fundamental knowledge on the adaptation and cross-species transmission of influenza virus. This has led to the design of novel attenuated influenza vaccines that target a diverse repertoire of viruses. Influenza virus, transmission, H1N1, swine, H9N2, immunity. Non-destructive 3D imaging to help mend broken hearts. Keratin-based dressings facilitate wound healing.
In addition, we will study the role of host and environmental factors in adaptation of avian influenza viruses to pigs. The occurrence and severity of a pandemic also depends on the immune status of the human population. Researchers had only identified viral particles for the first time less than 30 years before the height of the flu pandemic and the fledgling field of virology was just beginning to identify them as causes of disease in plants and animals.
Scientists were only first able to visualize a virus, the tobacco mosaic virus, after the invention of the electron microscope. Though the technology, knowledge and pace of research was different early in the 20th century, why did the discovery of influenza virus take so long?
In , veterinarian J. That work spurred the description of human influenza virus in They were able to connect the origins and evolution of the pandemic with viruses that circulate in other animals, particularly those from birds and the pigs examined by Dr.
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Just as seen in more recent outbreaks of new influenza viruses, the pandemic traced its origins to virus strains circulating in nature. The critical insight that led to the work reconstructing the virus had come in the s.
In birds and possibly other animals, influenza viruses are able to replicate and transmit to new hosts without causing any severe disease. On rare occasions, given the right circumstance, this new host is a different species. This cycle, common in many pathogens, is an important part of how virus is maintained in nature and explains how animals can be a reservoir for novel influenza viruses that can cause human illnesses. As researchers have sequenced the influenza viruses found in ducks and other birds, as well as people, swine and other animals, a picture of viral ecology based in nature has come into focus.
People were largely unaware that at the same time as the flu pandemic, pigs were sick with the disease and influenza viruses were also causing ongoing fowl plague epidemics. But the realization that influenza virus happily exists in a wild animal reservoir has influenced the way scientists study flu—and moreover, emerging disease of any sort.