Influenza A Virus Family: Orthomyxoviridae Genus: Influenzavirus
It can also be one of the deadliest.
Influenza A infections are characterized by abrupt onset of fever, sore throat, dry coughing, mylagia, headache, malaise, extreme fatigue, and muscle soreness. Most deaths caused by influenza are among the elderly and immunodeficient and are the result of secondary infections such as bacterial pneumonia. The incubation period for Influenza A is about 1-4 days, and the syndrome usually lasts for about 3-7 days. Influenza A is transmitted via the respiratory route.
If an individual has been infected with a similar strain within the past few years, then antibodies might neutralize the infecting virions. Anti HA antibodies such as IgA and IgG have been shown inhibit uncoating of the virus. However, if preexisting antibodies do not protect against the infection, activated macrophages and natural killer cells help recover from the infection.
A polyvalent inactivated vaccine is developed each year depending on the most common strains of influenza present during the last season. It is not cost effective and necessary to immunize the entire community, so only high risk cohorts (such as elderly, people with chronic debilitating diseases, and the immunodeficient) are usually vaccinated. Common side effects from the vaccine include local tenderness, and less commonly fever and malaise for a day. Efficacy is highest in the young and lowest in the old due to the idea of original antigenic sin. The vaccine is grown in embryonated hen’s eggs so those with egg allergies have contraindications to the vaccine; therefore a search for another effective vaccine is being researched, such as a live attenuated vaccine.
Game action: Oh no! An influenza epidemic…. If you got your annual influenza vaccine, then you win. If not, then you’ll be sick in bed this week!!!
Medical Virolgy by White and Fenner (1994) p 494-499
Principles of Virology by Flint, Enquist, Krug, Racaniello, and Skalka (2000) p 760