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Human swine influenza A(H1N1) - briefing

27 April 2009
by eub2 -- last modified 27 April 2009

Swine influenza (swine flu) is an acute viral infection of the respiratory tract in pigs caused by type A influenza virus. The mortality rate is low in pigs and recovery usually occurs within 7-10 days. Swine origin influenza viruses also occur in wild birds, poultry, horses and humans, but interspecies transmission is considered a rare event. So far three influenza type A virus subtypes: H1N1, H1N2 and H3N2 have been found in pigs.


Q1. Can swine influenza infect humans?

Yes. Human infections with swine influenza have been detected occasionally since the late 1950s usually in persons with direct exposure to pigs (e.g. people working in pig farms, etc.). In Europe, since 1958 a total of 17 cases have been reported. In the US, an outbreak of swine influenza virus
infections in humans was detected in recruits in a military camp in Fort Dix, New Jersey in 1976. A link to pigs was presumed but never discovered. Instead there was extensive human to human transmission, with over 200 infections resulting in 12 hospitalisations and one death.

Q2. What are the symptoms of swine influenza in humans?

Symptoms of swine influenza in humans are usually similar to regular human seasonal influenza symptoms, involving fever of sudden onset and respiratory symptoms, diarrhoea might also occur.

Q3. How do humans get infected?

Most commonly, swine influenza is transmitted through direct contact or close proximity with pigs. Secondary cases following human to human transmission have been reported in the past but they are very rare. This virus is not transmitted from eating pork or pork products.

Q4. Is there a vaccine against swine influenza?

Yes, there is a vaccine available for pigs against swine influenza, but there is no vaccine to protect humans from swine influenza.

Q5. Is the seasonal influenza vaccine effective against swine influenza?

There are certain similarities between the H1N1 human influenza viruses (covered by the seasonal vaccine) and the new H1N1 swine influenza viruses so one can not rule out some cross-protection. However, investigations need to be undertaken to determine whether this is the case. Those investigations are under way, but will take quite some time. 

Q6. Can swine influenza in humans be treated?

Most swine influenza viruses have been susceptible to antiviral medications such as neuraminidase inhibitors (oseltamivir and zanamivir) and older antiviral drugs (amantadanes). The virus that was currently detected in the US and Mexico is susceptible to neuraminidase inhibitors but resistant to amantadanes.

Q7. Why do the situations in the US and Mexico represent a new problem?

The novel swine influenza virus that has now been found in the two US states California and Texas and in Mexico contains pig, bird and human genes, in a combination that has never been observed before anywhere in the world. In addition there is a every indication that this virus has been transmitting from human to human and the resulting illnesses have been severe in a substantial number of cases in Mexico. 

Q8. What is the situation across Europe?

No cases have been detected in Europe so far. Cases were only reported in the US and Mexico.

Q9. What is being done about the situation?

The US Centers for Disease Control and Prevention (CDC) in Atlanta, the European Centre for Disease Prevention and Control (ECDC), the European Commission together with its Member States and the WHO Regional Office for Europe are monitoring and assessing the situation closely. The health authorities in Mexico are undertaking a number of measures for control and management of the outbreak such as closure of schools, advising avoidance of mass gatherings and distribution of antivirals. Furthermore, they have issued advice on hygienic measures to avoid the spread of influenza. The US public health authorities have also issued advice on hygienic
measures in the affected regions and have intensified the surveillance. In the EU, ECDC is following the epidemiological situation and assessing the risks and the European Commission working closely together with the EU Member States on all risk management issues within the Early Warning and Response System (EWRS). The Health Security Committee is also meeting to discuss the situation; The Global Health Security Initiative is exchanging information on the current status of the situation and counter-measures.

Q10. Are we facing a new influenza pandemic?

An influenza pandemic is characterised as an ongoing world-wide epidemic caused by a novel influenza virus that infects a large proportion of the human population lacking immunity to this virus. In the 20th century there have been three influenza pandemics in 1918, 1957 and 1968. 
In its Global Influenza Preparedness Plan the World Health Organisation (WHO) has defined six phases of pandemic alertness. Independent experts will now review the available evidence to determine whether the WHO Director General would be advised to change phase. The may conclude there is not enough information as yet to give such advise. 

In Europe in the past years there have been considerable efforts in pandemic preparedness planning and all European Members States have a national influenza pandemic preparedness plan.

Q11. Is it safe to travel to Mexico, California or Texas?

There is no statement from the World Health Organisation (WHO) or the US CDC concerning any travel restriction to the affected regions in Mexico, California or Texas. Persons who intend to travel to Mexico, California or Texas are advised to consult the WHO website and websites of their ministries of foreign affairs or national public health institutes. All travelers are advised to follow some general hygienic measures as listed below.

Q12. What can I do to protect myself if I want to travel to Mexico, California or Texas?

Travelers should follow standard precautions regarding respiratory infection if they travel to areas where human infections with swine influenza have been reported. All travelers to affected areas (currently parts of Mexico, California or Texas) should respect general hygienic measures such as:
•  Avoiding close contact with people who are sick. When you are sick, keep your distance
from others to protect them from getting sick too.
•  Staying home from work, school, and errands when you are sick. You will help prevent
others from catching your illness.
•  Covering your mouth and nose with a tissue when coughing or sneezing. It may prevent
those around you from getting sick.  Throw the tissue in the trash after you use it.
•  Washing your hands often will help protect you from germs.  Wash your hands often with
soap and water, especially after you cough or sneeze.  Alcohol-based hands cleaners may
also be effective. Avoid touching your eyes, nose or mouth. Germs are often spread when
a person touches something that is contaminated with germs and then touches his or her
eyes, nose, or mouth.
Q14. What precautions are needed for travelers returning from the affected areas in Mexico and the US (California, Texas)? Travellers returning from affected areas in Mexico and the US (California, Texas) should observe their personal health and if within seven days after return experience one or more of the symptoms listed below should immediately contact a physician. 
•  Fever
•  Respiratory symptoms such as cough or runny nose
•  Sore throat
•  Possibly other symptoms such as 
o  Body aches
o  Headache
o  Chills
o  Fatigue
o  Vomiting or diarrhoea (not typical for influenza but reported by some of the recent cases of swine influenza infection)

Source: European Centre for Disease Prevention and Control

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