pandemic influenza


Influenza (“flu”) is a respiratory illness that can be transmitted from person to person. Flu viruses are of two main genetic types: Influenza A and B. Influenza A strains are further identified by two important surface proteins that are responsible for virulence: hemagglutinin (H) and neuraminidase (N).

Swine flu occurs naturally and may cause outbreaks among wild and domestic swine. People do not normally get swine flu, but each year CDC identifies a few isolated cases of human flu that are caused by flu strains typically associated with swine.

What is swine influenza?
Swine influenza is a respiratory disease of pigs caused by type A influenza viruses. In affected pigs, it causes cough, fever, nasal discharge, lethargy and difficulty breathing. Influenza A viruses are classified by two components of the viral surface, hemagglutinin (H) and neuraminidase (N). Different types of influenza A viruses are infectious to avian and mammalian species. Pigs and people are susceptible to influenza A viruses from both avian and mammalian sources. Infection with multiple viruses can lead to the creation of new “reassorted” viruses with components of pig, bird and human flu origin. Classical swine flu (H1N1) was first isolated in 1930, and many other subtypes have since been identified (e.g. H3N2, H1N2). In the United States, swine influenza outbreaks are most common in fall and winter. In Minnesota, we see peaks of swine flu activity in April through May and September through November.

Avian flu (“bird flu”) is caused by viruses that occur naturally among wild birds, and that may also affect domestic poultry. In 1997 a new H5N1 strain of avian flu emerged in Asia, and has since caused millions of deaths among domestic poultry, and hundreds of deaths in humans. Health officials have been concerned that this strain could cause a human pandemic, and governments around the world have carried out a number of preparedness activities, including vaccine development and stockpiling, and planning for continuity of services.

Pandemic flu is caused when a novel strain of human flu (i.e., one that spreads from person to person) emerges and causes a global outbreak, or pandemic, of serious illness. Because there is little natural immunity, the disease is often more severe than is typical of seasonal flu.

Influenza is an infectious disease caused by the influenza virus. The disease is commonly called flu or grippe. The word influenza is sometimes used to refer generally to either influenza or similar illnesses. The symptoms of influenza include chills, fever, headache, aches, and weakness. The symptoms usually disappear in about a week. The patient's resistance may be lowered, so that secondary infections, such as bacterial pneumonia, follow the influenza.

How influenza spreads. Influenza is mainly a respiratory disease. The virus is inhaled and comes in contact with cells of the upper air passages. It penetrates the cells that line these passages and reproduces within them. In time, new influenza viruses are released from the infected cells and infect other cells along the respiratory tract. Influenza may spread deep within the lungs. The virus may also be carried away in exhaled air and infect other people.

One of the worst global epidemics of influenza occurred in 1918-1919. About 20 million people, including more than 500,000 Americans, died in this epidemic. In 1957-1958, Asian flu caused a worldwide epidemic, as did Hong Kong flu in 1968-1969. Far fewer deaths resulted from these epidemics, due largely to the control of secondary infections with antibiotics.




What is pandemic influenza A(H1N1) 2009 virus?

This is a new influenza A (H1N1) virus that has never before circulated among humans. This virus is not related to previous or current human seasonal influenza viruses. It has also been called “swine flu” and “novel flu”.


The virus is spread from person-to-person. It is transmitted as easily as the normal seasonal flu and can be passed to other people by exposure to infected droplets expelled by coughing or sneezing that can be inhaled, or that can contaminate hands or surfaces. To prevent spread, people who are ill should cover their mouth and nose when coughing or sneezing, stay home when they are unwell, clean their hands regularly, and keep some distance from healthy people, as much as possible.

Typical signs and symptoms of infection

Signs of pandemic influenza A(H1N1) 2009 are flu-like, including: fever, cough, headache, muscle and joint pain, sore throat and runny nose, and sometimes vomiting and diarrhoea.

Public health concerns about the new virus

Seasonal influenza occurs every year and the viruses change each year - but many people have some immunity to the circulating virus which helps limit infections. South Africa also uses seasonal influenza vaccines to reduce illness and deaths. But pandemic influenza A/H1N1 2009 is a new virus and one to which most people have no or little immunity and, therefore, this virus could cause more infections than are seen with seasonal flu.
The new pandemic influenza virus appears to be as contagious as seasonal influenza, and is spreading fast particularly among young people (from ages 10 to 45). The severity of the disease ranges from very mild symptoms to severe illnesses that can result in death. The majority of people who contract the virus experience the milder disease and recover without antiviral treatment or medical care. Of the more serious cases, more than half of hospitalized people had underlying health conditions or weak immune systems. The overall severity of the influenza pandemic has been assessed to be moderate.

It is now clear that the pandemic virus has been established throughout the country, and that sustained community transmission is inevitable. Moving forward, a strategy that concentrates on the detection, laboratory confirmation, and investigation of all cases, including those with mild illness, is extremely resource-intensive thus leaving little capacity for the monitoring and management of severe cases. In addition it diverts limited resources away from managing other diseases such as HIV and TB. In line with a World Health Organization (WHO) recommendation, it has now been decided to stop routine laboratory testing of all suspected cases of pandemic influenza infection.

Source :
The National Institute for Communicable Diseases (NICD) of the National Health Laboratory Service (NHLS) In collaboration with: The South African National Department of Health and World Health Organisation (WHO).

What is swine influenza?
Influenza Defined
Influenza Viruses - Types, Subtypes, and Strains
What is pandemic influenza A(H1N1) 2009 virus?
Definitions for identification of pandemic influenza A(H1N1) 2009
Case Management & Infection Control
Who should be tested?
Step-by-step guide for specimen collection, storage and transportation
Doctors/Nurses directions to Patients/Parents
How Influenza Viruses Change: Drift and Shift
The 2009 Influenza Pandemic
International Health Regulations
Vaccine Development and Use
Naming the Virus Strain
Information for Families and Visitors
New Pandemic Influenza A (H1N1) 2009
Pandemic (H1N1) 2009 Influenza Guidance
Recent Results from Studies with the new 2009 A/H1N1 Influenza A Virus
Continued pandemic influenza virus detections across Europe with increased activity in the UK (Northern Ireland)
Highly Pathogenic Avian Influenza Virus H5N1 and Wild Birds