Influenza pandemic is mainly caused by -
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Influenza 

Influenza is an acute respiratory tract infection caused by influenza virus.
There are three viral subtypes


Type A → Causes all Pandemics and most of the epidemics
Type B → Can cause epidemics
Type C → Causes endemic infection


Three types of influenza viruses are circulating in world → A (H1N1), A (H3 N2) and B
A New type has been recognized → A (H5 N1)
Source of infection → case or subclinical case
Mode of transmission → Droplet infection by respiratory route
Incubation period →18-72 hours

Clinical manifestations

Most infections are subclinical
fever, headache and myalgia
Respiratory → coughing
There is no virernia

Complications

Pneumonia → M.C. by str. pneumoniae
Worsening of COPD
Encephalitis
Reye's Syndrome → with type B virus
GB. Syndrome
G I Symptoms (gastric flu) → type B virus

Laboratory diagnosis

Most commonly, the diagnosis is established by the use of rapid viral tests that detect viral nucleoprotein or neuraminidase   - Harrison - 1069
Best specimen is nasopharyngeal secretion.
Type A
Type B
Type C
All