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Influenza Virus

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The influenza virus and Streptococcus pneumoniae are two of the most common pathogens to affect humans; both generally pose no major concern to human life but have the potential to cause catastrophic damage to the lives of susceptible individuals. With many strains of the influenza virus being a constant presence around the world, and S. pneumoniae being a normally harmless commensal bacterium residing in the nasal cavities and upper respiratory tract of healthy individuals , it is likely impossible to quell the spread of either pathogen and so treatments must be found to ensure those with detrimental risk factors are either protected or receive sufficient medical attention in a timely manner in order to prevent irrevocable damage.
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There are two important proteins used in the determination of the type of influenza; haemagglutinin (HA) and neuraminidase (NA). There are 18 known variations of the haemagglutinin protein and 11 of the neuraminidase protein, giving hundreds of possible variations in the subtypes of the virus . These subtypes are further divided into different strains that have a divergent molecular makeup, giving rise to viruses that differ in virulence, ease of transmission and severity of symptoms. Not all strains of influenza can cause disease in humans; influenza D subtypes cannot infect humans and influenza C infections are rare and usually very minor. Influenza A and B are the subtypes that are responsible for the common infections and the epidemics and pandemics that occur periodically, with influenza A causing the majority of these infections. The virus is transmitted through the inhalation of droplets which are expelled when an infected person coughs or sneezes, through contact with a contaminated surface and through the exchange of saliva . The infected person becomes infectious to others around 12 hours after first contact with the virus and remains contagious for around the next five days; this can vary as the immunocompromised can take longer to subdue the virus and children tend to be more infectious than adults . The virus incubates in the respiratory tract by invading cells through the cleavage of the viral protein haemagglutinin by human proteases . The pathogenicity of a certain strain is determined by the spread of proteases in the respiratory tract that can cleave the proteins of the virus; a strain is typically milder if the proteases that reside in the lungs and throat are the only ones capable of cleaving the virus, causing an upper respiratory tract (URT)

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