Swine flu

When a person is said to have “swine flu”, they in fact have a “normal” flu caused by influenza A viruses. The term “swine flu” originates in 2009, when an influenza virus normally occurring only in pigs acquired new genetic features that allowed it to be transmitted to humans and caused a global outbreak of flu.

At a glance

  • Swine flu is the name commonly used to denote the flu virus that caused a global pandemic in 2009.
  • This pandemic was caused by the appearance of a new strain of flu virus in humans, which showed characteristics of the flu viruses that occur in pigs.
  • Pigs are susceptible to various flu viruses. They serve as a “mixing bowl”, in which viruses exchange genetic information, leading to the development of new virus subtypes that can be transmitted to humans.
  • Normally, influenza viruses are not easily transmitted from animals to humans. However, when this happens, it is known as zoonotic influenza.
  • The symptoms and treatment are the same as those for seasonal flu.
  • For people with pre-existing conditions, the infection may be severe or even fatal.

Note: The information in this article cannot and should not replace a medical consultation and must not be used for self-diagnosis or treatment.

A man with pigs in a pig stall.

What is swine flu?

Swine flu is simply a “normal” viral flu infection. It is caused by the virus strain known as influenza A(H1N1)pdm09. It was detected for the first time in 2009, leading to a pandemic of flu that became commonly known as “swine flu”. The virus has since become one of the causes of seasonal flu outbreaks.

Influenza (flu) viruses are common in humans, birds and pigs. It is primarily viruses belonging to the influenza A and B groups that make people ill. Animals are only affected by influenza A viruses.

It is rare for people to become infected and ill with flu viruses from pigs.

In very rare cases, humans can be infected with flu viruses from pigs and become ill as a result. In contrast, animals can very easily be infected with human influenza A viruses and develop symptoms. Infections occur primarily in pig farming due to close contact with infected workers.

Pigs, birds and people can be infected with various flu viruses at the same time. If different virus subtypes come into contact with one another, they may exchange genetic information and create new types of flu viruses. In some cases, these viruses can be transmitted to humans and spread in the population – as was the case in the 2009 pandemic.

If flu viruses pass from an animal to a human and cause illness, this is known as zoonotic influenza.

These kinds of flu infections can occur during the “classic” flu season between December and April – but may also appear at other times of the year.

What are the symptoms of swine flu?

Flu viruses in pigs (i.e., swine flu viruses) can be transmitted to a human who comes into close contact with an infected animal. However, this is rare. Swine flu viruses are not normally transmitted from one person to another.

The first symptoms appear between 1 to 5 days after infection. These include:

  • fever
  • coughing, shortness of breath
  • nausea, vomiting, diarrhea
  • less commonly – sore throat, headache and limb pain

Overall, the symptoms tend to be mild and are comparable to those of seasonal flu. However, severe or fatal forms of the illness may develop in people with pre-existing conditions.

People who develop a severe form often develop pneumonia, which is sometimes complicated by an additional bacterial infection. Treatment in hospital may be necessary.

What causes swine flu?

Whenever a flu is passed from an animal to a human, it is always caused by influenza A viruses. While influenza B viruses can also make people ill, they only occur in humans. There are several subtypes of influenza A viruses, which differ in their H (hemagglutinin) and N (neuraminidase) components.

When a person catches the flu, it is normally caused by a virus of the subtype H1N1 or H3N2. The same subtypes also occur in pigs. Despite this, the flu viruses occurring in pigs are still so different from those in humans that they rarely cause illness in people. Infections only occur due to close contact with infected animals. Most people affected work in pig farming, in slaughterhouses or in veterinary practices.

Important: Eating pork or pork products is not associated with contracting swine flu.

The genetic information of flu viruses is found in several small sections called segments. If various influenza subtypes come into contact with one another, they can exchange individual segments of genetic information. This produces viruses with new combinations of genetic information. This process occurs more easily in pigs because they are susceptible not only for swine flu viruses but also to flu viruses from birds (avian flu viruses) and humans.

Due to slight changes in the viruses’ genetic information, different flu variants appear and cause seasonal flu outbreaks every year. If an entirely new combination occurs containing segments of animal flu viruses that can also spread in humans, this can lead to a flu pandemic. The “Spanish flu” of 1918 was also caused by an influenza A virus of the type H1N1.

Which people are particularly at risk from swine flu?

Swine flu viruses that are passed on to humans often only cause mild symptoms. The following groups of people are at an increased risk of developing a severe or fatal illness:

  • children younger than 5
  • people over the age of 65 and people who have been taking medication containing the active agent acetylsalicylic acid (ASA) for an extended period
  • people with compromised immunity as a result of having an illness such as AIDS or taking medication that suppresses the immune system
  • pregnant women, especially those in the third trimester
  • people with chronic conditions, such as asthma, COPD, obesity, diabetes, heart disease or neuromuscular diseases

How common is swine flu?

It is rare for people to be infected with swine flu viruses.

In Germany, only 5 infections were detected between 2007 and 2011. Globally, 37 illnesses were documented in humans between 1958 and 2005.

What can be done to prevent swine flu?

Components of the virus that caused the swine flu pandemic in 2009 have already been incorporated into the regular seasonal flu vaccines.

There is no vaccine against individual flu viruses that are passed from pigs to humans. More particularly, a flu vaccine is ineffective against new combinations of influenza viruses because new vaccines can only be created when the composition of the viruses is known.

For more information about seasonal flu vaccines, see gesundheitsinformation.de.

There are also many hygiene measures that can be taken to prevent infection with swine flu viruses.

Transmission of these viruses can be prevented by:

  • keeping pigs in the best possible conditions and creating a healthy housing climate
  • vaccinating the animals against flu
  • ensuring that any animals that may be infected do not have any contact with unvaccinated pigs or other farm or wild animals
  • ensuring that workers who come into contact with pigs receive a seasonal flu vaccine every year

Person-to-person transmission can be prevented by:

  • coughing into the elbow when sneezing or coughing to minimize the amount of virus particles released into the air
  • washing and sanitizing hands regularly
  • disinfecting surfaces that may be contaminated with viruses
  • avoiding contact with others when ill, staying home from work and avoiding use of public transport

How is swine flu diagnosed?

An infection with a swine flu virus may be suspected if a person shows typical symptoms of flu and has had close contact with pigs. This mostly affects people who work with pigs as part of their job. Swine flu is suspected in particular if the symptoms occur outside of the flu season.

Swine flu is suspected if a person shows typical symptoms of flu and has had close contact with pigs.

Doctors can take a sample of fluid from the nose or a nasal and throat swab and perform a rapid test in the doctor’s office itself. However, this test only detects flu viruses and doesn’t distinguish between different subtypes.

If it is suspected that the person has contracted flu from a pig or if swine flu is confirmed, the health authorities are notified. Experts at the national reference center for influenza will then analyze the samples taken in greater detail. This allows them to determine whether the virus represents a new combination of genetic information.

How is swine flu treated?

People can generally recover from swine flu at home. It’s important to get rest and plenty of fluids, in particular in the case of a high temperature.

Antipyretic (fever-reducing) painkillers help relieve headache and limb pain. If symptoms become significantly worse, medical treatment should be sought.

If a patient is suffering with flu caused by a swine flu virus, doctors can use antiviral drugs to prevent the flu viruses from replicating. These include the active agent oseltamivir from a group of drugs known as neuraminidase inhibitors. In the best-case scenario, the drugs will shorten the length of the illness. However, they are only effective if treatment is started within the first 48 hours after the onset of symptoms.

In cooperation with the German Society of Virology (Gesellschaft für Virologie e.V.). As at:

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