This document provides an overview of influenza, including its history, types, epidemiology, prevention and control. It discusses how influenza was first described in ancient times and the discovery of the influenza virus in the 1930s. It describes influenza as a contagious respiratory illness caused by influenza viruses that can range from mild to severe and sometimes deadly. It outlines the three main types of influenza viruses (A, B and C), and notes that type A is responsible for all known pandemics and some animal strains can infect humans. The document also classifies influenza viruses according to their hemagglutinin and neuraminidase proteins and which subtypes are known to infect humans.

1. INFLUENZA Epidemiology,
Prevention and Control

2. • Contents 1. History 2. About the disease and types 3. Epidemiological trends
4. Prevention and Control. 5. Pandemic Influenza(h1n1) 2009 6. Special-
avian Influenza(outbreaks). 7. Newer vaccines and strains.

3. • History of influenza • 412 BC -
first mentioned by Hippocrates •
1580 - first pandemic described •
1580-1900 - 28 pandemics 3
Discovery of Influenza Virus •
First isolated from a pig in 1931
(swine flu) • Isolated from human
in 1933

4. • WHAT IS INFLUENZA? (ALSO KNOWN AS THE
FLU) • The flu is a contagious respiratory illness • It is
caused by influenza viruses • It can cause mild to severe
illness and at times can lead to death • It can be
prevented by getting the flu vaccination each year
Influenza: A Viral infection • Acute respiratory infection
caused by Influenza virus – Three types A, B and C. •
Currently viruses circulating in human population –
Influenza A (H3N2), A (H1N1) and B Strains. • All
known pandemics (global outbreaks) were caused by
Influenza A. • Animal influenza viruses may affect
humans in special circumstances – Bird Flu: A (H5N1).

5. • Naming influenza viruses A/Hong
Kong/156/97 (H5N1) Strain ID Type
Hemagglutinin Neuraminidase Origin
Year isolated 16 9 7 Influenza types Type
A Potentially severe illness Epidemics and
pandemics Rapidly changing Type B
Usually less severe illness Epidemics More
uniform Type C Usually mild or
asymptomatic illness Minimal public
health impact

6. Classification of Influenza virus • Classified on the basis of
hemagglutinin (HA) and neuraminidase (NA). • 16 subtypes of HA
and 9 subtypes of NA are known to exist in animals (HA 1-16, NA
1-9). • 3 subtypes of HA (1-3) and 2 subtypes of NA (1- 2) are
human influenza viruses. HA 5, 7, 9 and NA 7 can also infect
humans

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