Pandemic potential new influenza virus isolated in pigs

• 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. 
• According to a US journal, the study 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 (animal models for pathogenesis). 

What is Reassortment?

• Reassortment of viruses is a mechanism through which new strains of virus are generated. These strains have new properties and can cause pandemics. 
• The swine influenza viruses have many lineages. 
• Eurasian-avian (EA) is the most dominant one among them .  
• The 2009 pandemic virus went back to pig herds after the outbreak. 
• Reassortants 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 new genotype (G4)

• The new genotype (G4) of this EA strain of H1N1 virus produced due to reassortment was found to have acquired increased human infectivity. 
• The current infectivity of all the new emergent EA reassortants in human populations was unknown. 
• G4 reassortant has all the essential hallmarks of a candidate pandemic virus similar to the 2009 pandemic virus.
• Human-to-Human transmission is possible for this reassortant.
• G4 virus could efficiently infect human airway epithelial cells found in the respiratory system. 
• Replicability in normal human bronchial epithelial cells and alveolar epithelial cells is also found in the respiratory system. Both are incidentally major targets of influenza virus infection.
• 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

• The transmissibility potential of any virus is dependent on the fact as to how effective human-to-human transmission would be. 
• 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). 
• It has the capability of binding to human-type receptors like the SARS-CoV-2. Incidentally, aerosol transmission has not been confirmed for the novel coronavirus SARS-CoV-2.

Will pre-existing immunity against influenza viruses protect against G4? 

• 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. 
• G4 types are antigenically distinct from the existing influenza strains. 
• Therefore, the existing seasonal influenza vaccines will provide no immunity against the new gene. 
• So far, there are five human cases of EA strain in China, of which, two belonged to the G4 type.