Human-to-human transmission possible, pre-existing immunity against flu of no help
Scientists have identified a new ‘re-assorted’ influenza virus from pigs in China that has pandemic potential. The virus has shown ‘increased human infectivity’ in swine industry workers.
The study, which has been published in Proceedings of National Academy of Sciences, a US journal, was based on extensive surveillance done among pig populations in 10 provinces of China from 2011-2018.
The serological exercise showed that the new gene of the H1N1 virus has efficient infectivity and transmissibility in ferret models.
Basically, “reassortment” of viruses is a mechanism through which new strains of virus are generated that have new properties and can cause large scale epidemics; even pandemics.
The swine influenza viruses have many lineages out of which Eurasian-avian (EA) is the most dominant one. The 2009 pandemic virus went back to pig herds after the outbreak.
“Subsequently, re-assortants between the swine EA H1N1 virus and human pandemic/09 H1N1 virus have been sporadically detected in pigs in China and other countries, some of which have caused human infections in China,” the paper read.
The new genotype (G4) of this EA strain of H1N1 virus produced due to reassortment was found to have acquired increased human infectivity. However, the current infectivity of all the new emergent EA re-assortants in human populations was not known. The researchers also clearly say that similar to the 2009 pandemic virus, G4 reassortant has all the essential hallmarks of a candidate pandemic virus.
Human-to-Human transmission possible
G4 virus could efficiently infect human airway epithelial cells found in the respiratory system. The researchers also assessed replicability in normal human bronchial epithelial cells and alveolar epithelial cells also found in the respiratory system. Both are incidentally major targets of influenza virus infection.
They found that the replicability level of the G4 gene was similar to the 2009 pandemic virus at each point in time and produced virus progeny after 36-60 hours of seeding of infection. The post-mortem further revealed that the G4 virus caused much more damage to the lungs as compared to the 2009 pandemic virus.
The transmissibility potential of any virus is dependent on the fact as to how effective human-to-human transmission would be. To analyse this, the researchers performed transmission experiments on ferrets through direct contact and through respiratory droplets.
The 2009 pandemic virus was found to be efficiently transmitting between ferrets through both the mediums. As far as the G4 type was concerned, all the four variants of this gene showed effective transmission through direct contact. Three of four variants of the G4 showed effective transmission through respiratory droplets too.
The researchers also confirmed aerosol transmission in G4. Aerosols are liquid particles having viruses and tend to sustain in the air for some time. Incidentally, aerosol transmission has not been confirmed for the novel coronavirus SARS-CoV-2.
Will pre-existing immunity against influenza viruses protect against G4? The researchers found answers in the negative. Whether pre-existing immunity against one form of a virus will work as a shield against new types depends on the fact as to how much the ‘drift’ or change is in the antigenic properties in the latter.
The researchers found that G4 type are antigenically distinct from the existing influenza strains. Therefore, the existing seasonal influenza vaccines will provide no immunity against the new gene.
So far, the researchers have found five human cases of EA strain in China, of which, two belonged to the G4 type.
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