Types of Influenza (Flu) Affecting Humans

Seasonal, Swine and Bird Flu in Humans

Types of influenza currently appearing in humans include:

  • Seasonal influenza, also called annual influenza, conventional influenza, common flu or human flu
  • Swine flu, also called novel flu (in Europe), or 2009 pandemic influenza A H1N1
  • Bird flu or avian influenza

Table 1: Main characteristics of seasonal, swine and bird flu.

INFLUENZA TYPE and CAUSESEASON and WAY of SPREADSERIOUS COMPLICATIONSVACCINE
SEASONAL (ANNUAL, CONVENTIONAL) INFLUENZA or COMMON or HUMAN FLU

Influenza A, B and, rarely, C virus
November – April, but can appear year-round

Human to human, by inhaling droplets from infected and coughing or sneezing persons, or by touching surfaces, like doorknobs, keyboards, etc. up to 8 hours after their contamination, and transferring them to mouth, nose, eyes. Seasonal flu usually does not spread from animals to human.
Complications mainly appear only in risk groups: children 6-23 months, people after 65 years or with chronic diseases; usually not in otherwise healthy people 2 – 65 years old1. The ‘flu shot’ – an inactivated vaccine (containing killed human influenza virus) given with a needle into a (shoulder) muscle.

2. The nasal spray or LAIV (Live Attenuated Influenza Vaccine) with a weakened but live human influenza virus.
SWINE FLU or 2009 PANDEMIC NOVEL H1N1 INFLUENZA

Influenza A virus, subtype swine H1N1 influenza virus
Year-round

Human to human by droplet infection; not from animals to human (1); not from properly cooked pork or other food
Complications are possible in anyone1. The ‘flu shot’, containing killed swine H1N1 virus, given with a needle into the shoulder

2. The nasal spray (LAIV vaccine) containing weakened, but live swine H1N1 virus.
BIRD FLU or AVIAN INFLUENZA

Influenza A virus, subtype H5N1
Year-round

Close contact with nasal secretions, saliva or feces of domestic birds orfrom raw poultry meat; currently not from human to human
Complications are possible in anyoneVaccine is currently not available

During 2009 influenza H1N1 (swine flu), spread of infection from pigs to human was not documented in any case; all infections were supposedly spread from human to human (2). In few cases, spread of swine flu from humans to pets was documented, though.

Canine influenza (dog flu) and equine influenza (horse flu) are caused by various types of Influenza A H3N8 virus. Dog flu spreads only among dogs, and horse flu only among horses. None of them currently spread to humans.

NOTE:

  • Symptoms of all types of influenza are roughly the same: body aches, tiredness, headache, fever, runny nose and sore throat. Fever does not always appear in influenza!
  • Diagnosis. The type of influenza cannot be determined from symptoms, but only by laboratory tests of the mucus.
  • Serious complications of all types of influenza may include: pneumonia, inflammation of the muscles (myositis), heart sac (pericarditis), heart muscle (myocarditis), brain membranes (meningitis), brain (encephalitis), and worsening of an existing chronic disease.
  • Human influenza H1N1 virus causing human flu, and swine flu H1N1 virus causing swine flu are two different types of viruses. They can both cause a disease in humans and pigs, though.
  • Seasonal flu vaccines do not protect against swine flu, and swine flu vaccines do not protect against seasonal flu.

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References:

  1. WHO about 2009 H1N1 influenza: Spread of swine flu from pigs or other animals to human was not documented (who.int)
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