Influenza - background

Intro

influenza → myxovirus → family of viruses: Orthomyxoviridae

originally found in aquatic birds

transitioned to humans 6000 - 9000 years ago (rise of farming and urbanisation)

name derived from Italian word for influence

Medieval Understanding of Influenza

some people believed that it was caused by alignment of the stars

influenza epidemics occuring at irregular periods seemed to support this theory

people knew that some diseases were infectious/could transmit to other people (despite not knowing the cause)

would quarantine for infectious disease

Defining Influenza

Influenza virus: small size; genetic material is RNA; outer envelope comes from plasma membrane from host cell and contains viral proteins

after 1890 flu pandemic, H. influenzae (a bacterium) was incorrectly identified as the cause of influenza

H. influenzae was found in casualties in 1918 flu pandemic, seeming to support the theory

Experiments in the early 1930s proved that H. influenzae did not cause flu, although it does make it worse

Influenza in Humans

acute viral disease affecting respiratory tract

spread by aerosol droplets from coughing and sneezing

symptoms: fatigue, muscle/joint pains, fever

Stages of infection:

  1. Person gets infected
  2. Virus replicates in the cells lining upper and lower respiratory tract
  3. 1-2 days later: virus production peaks
  4. Following 3-4 days: virus particles shed, symptoms at their most severe
  5. After 1 week: virus is no longer produced (but antigens are still detectable for another week)
  6. 3-4 days post infection: antibodies to virus start appearing in the blood
  7. After 2 weeks: virus completely eliminated

Most at risk: infants, older people, those with underlying disease; can be fatal to these groups

flu epidemics can cause thousands of deaths

fatality rate of epidemics depends on strain of flu

Influenza infection of other species

many species can be infected by influenza viruses

most species have an acute infection from influenza virus

most mammals have similar symptoms to humans (and acute respiratory tract infection)

Wild ducks and aquatic birds

virus infects gut

do not appear to have physical symptoms

remain infected for 2-4 weeks

virus is shed in feces

Hybrid Strains

influenza viruses sometimes form hybrid strains including genes from different species-specific strains

pool of viruses in other species acts as genetic resevoir

areas with animal-human contact like parts of South-east/ East Asia are often source of hybrid strains