Three major players:
Influenza A viruses:
- Undergo genetic drift to cause seasonal epidemics.
- Genetic shift in influenza A viruses is responsible for global pandemics.
- Can infect humans and other animals.
- Transmission: air-borne respiratory droplets. These can be inhaled directly or may be initially picked up by the hands from contaminated surfaces then spread by touching the facial area.
- Signs and Symptoms: After a 24-48 hour incubation period, sudden onset of illness characterized by fever, mylagias, headache, sore throat, and cough. People usually recover spontaneously after 4-7 days, though bacterial pneumonia is a serious complication that increases duration and severity of illness.
- Prevention: vaccination and chemoprophylaxis
- Treatment: adamantanes
Influenza B viruses:
- Infection limited to humans
- Does not cause pandemic disease
- Undergo genetic drift more slowly than infleunza A viruses, but they still have epidemic potential. Influenza B epidemics are generally less severe than those caused by type A.
- Transmission: same as influenza A
- Signs and Symptoms: same as influenza A with the additional complication of Reye’s syndrome.
- Prevention: vaccination
- Treatment: neuraminidase inhibitors
Influenza C viruses:
- Infect humans only
- Cause mild respiratory tract infections.
- Are not responsible for serious disease or outbreaks.
Antibody produced by the body’s immune response to one type or subtype (within influenza A) of influenza gives limited or no protection against other types or subtypes.