Influenza viruses

Influenza viruses (commonly known as flu) infect a wide range of hosts, including humans and swine, but the natural reservoir lies in populations of wild aquatic birds such as ducks and shorebirds. Influenza viruses are members of the family Orthmyxoviridae, and exist as three types; Influenza Type A, Type B and Type C.

The types are subdivided into categories (strains) depending on the outer proteins H (Haemagglutinin) and N (Neuraminidase). These outer proteins can be combined to create different strains, for example, H1N1, H5N1, H9N2. Each strain can infect a certain set of animals, but the viruses can sometimes rearrange to infect other species. Influenza viruses have a single stranded RNA genome that is spilt into eight different segments. It is surrounded by an envelope and a capsid.

Associated diseases:

Influenza viruses cause the flu; symptoms can vary depending on the animal infected, the immune response and the virulence of the strain.

Clinical signs:

  • Fever
  • Coughing, sneezing, difficulty breathing
  • Fatigue
  • Loss of appetite

When Influenza strains rearrange they can create particularly devastating outbreaks of flu, which can result in more severe symptoms and can even lead to death.

Disease transmission:

Influenza viruses can be spread by direct contact with infected individuals, by inhaling contaminated aerosols produced by coughing and sneezing and through contact with contaminated objects (fomites).

Disease prevalence:

The virus can be globally spread, with temperate climates having seasonal epidemics mainly during winter while in tropical regions outbreaks are more sporadic. It is estimated that these annual epidemics result in about 3 to 5 million severe human cases of illness, and about 250,000 to 500,000 deaths. Occasionally particularly virulent strains can surface which can cause pandemics such as the ‘Spanish flu’ in 1918 which caused upwards of 50million deaths.  

Impact for Society – what are we doing?

The viruses responsible for all four of the worldwide human influenza pandemics seen in the last 100 years have originated from birds. In addition to causing illness amongst humans, severe declines in productivity in agricultural industries such as the poultry and swine can be seen when outbreaks of avian and swine flu occur.

The Institute specialises in livestock viral diseases and as such works on both avian and swine flu to protect both livestock and human populations. Research is concerned with improving the speed and accuracy of flu diagnostics, and creating a new universal vaccine that would potentially be able to protect against all strains of flu.


Downloadable factsheet

* Image by Cynthia Goldsmith courtesy of Public Health Image Library (PHIL)

Research papers

James J, Howard W, Iqbal M, Nair V, Barclay W S, Shelton H (2016)

Journal of General Virology 97 (10) , 2516-2527
Thuy D M, Peacock T P, Bich V T N, Fabrizio T, Hoang D N, Tho N D, Diep N T, Nguyen M, Hoa L N M, Trang H T T, Choisy M, Inui K, Newman S, Trung N v, van Doorn R, To T L, Iqbal M, Bryant J E (2016)

Infection, Genetics and Evolution 44 , 530-540
Morgan S B, Hemmink J D, Porter E, Harley R, Shelton H, Aramouni M, Everett H E, Brookes S M, Bailey M, Townsend A M, Charleston B, Tchilian E (2016)

Journal of Immunology 196 (12) , 5014-5023
Wyde P R, Guzman E, Gilbert B E, Couch R B (2001)

4th World Congress on Options for the Control of Influenza, Crete, Greece. 1219 , 999-1005
Ayora-Talavera G, Shelton H, Scull M A, Ren J, Jones I M, Pickles R J, Barclay W S (2009)

PLoS One 4 (11) , e7836


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