Swine Influenza (swine flu) is a respiratory disease of pigs caused by type A influenza virus that regularly causes outbreaks of influenza in pigs. Swine flu viruses cause high levels of illness and low death rates in pigs. Swine influenza viruses may circulate among swine throughout the year, but most outbreaks occur during the late fall and winter months similar to outbreaks in humans. The classical swine flu virus (an influenza type A H1N1 virus) was first isolated from a pig in 1930.
Swine influenza viruses are most commonly of the H1N1 subtype, but other subtypes are also circulating in pigs (e.g., H1N2, H3N1, H3N2). Pigs can also be infected with avian influenza viruses and human seasonal influenza viruses as well as swine influenza viruses. The H3N2 swine virus was thought to have been originally introduced into pigs by humans. Sometimes pigs can be infected with more than one virus type at a time, which can allow the genes from these viruses to mix. This can result in an influenza virus containing genes from a number of sources, called a "reassortant" virus. Although swine influenza viruses are normally species specific and only infect pigs, they do sometimes cross the species barrier to cause disease in humans.
The strain of influenza virus recently identified in Mexico and USA is unique because it is a combination of genes from swine, bird, and human influenza viruses.
Spread of this swine influenza A (H1N1) virus is thought to be happening in the same way that seasonal flu spreads. Flu viruses are spread mainly from person to person through coughing or sneezing of people with influenza. Sometimes people may become infected by touching something with flu viruses on it and then touching their mouth or nose.
The disease is considered endemic in the United States. Outbreaks in pigs are also known to have occurred in North America, South America, Europe (including the UK, Sweden, and Italy), Africa (Kenya), and in parts of eastern Asia including China and Japan.
The United States Government has reported seven confirmed human cases of Swine Influenza A/H1N1 in the USA (five in California and two in Texas) and nine suspect cases. All seven confirmed cases had mild Influenza-Like Illness (ILI), with only one requiring brief hospitalization. No deaths have been reported.
The Government of Mexico has reported three separate events. In the Federal District of Mexico, surveillance began picking up cases of ILI starting 18 March. The number of cases has risen steadily through April and as of 23 April there are now more than 854 cases of pneumonia from the capital. Of those, 59 have died. In San Luis Potosi, in central Mexico, 24 cases of ILI, with three deaths, have been reported. And from Mexicali, near the border with the United States, four cases of ILI, with no deaths, have been reported.
Of the Mexican cases, 18 have been laboratory confirmed in Canada as Swine Influenza A/H1N1, while 12 of those are genetically identical to the Swine Influenza A/H1N1 viruses from California.
The majority of these cases have occurred in otherwise healthy young adults. Influenza normally affects the very young and the very old, but these age groups have not been heavily affected in Mexico.
Preventive measures include:
1. Avoid close contact.
Avoid close contact with people who are sick. When you are sick, keep your distance from others to protect them from getting sick too.
2. Stay home when you are sick.
If possible, stay home from work, school, and errands when you are sick. You will help prevent others from catching your illness.
3. Cover your mouth and nose.
Cover your mouth and nose with a tissue when coughing or sneezing. It may prevent those around you from getting sick.
4. Clean your hands.
Washing your hands often will help protect you from germs.
5. 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.
6. Practice other good health habits.
Get plenty of sleep, be physically active, manage your stress, drink plenty of fluids, and eat nutritious food.
Advice for Travellers Recommendations for travellers
1. Wash your hands
By washing your hands with soap under warm running water, you will reduce your chance of getting the flu.
Alcohol-based hand gel can also be used if soap and water are not readily available. It's a good idea to keep some with you in your pocket or purse when you travel.
2. Practice proper cough and sneeze etiquette
Cover your mouth and/or nose to reduce the spread of germs. Remember to wash your hands afterwards.
3. Try to avoid close contact with sick people
Cover your mouth and nose to reduce the spread of germs. Remember to wash your hands afterwards.
4. Monitor your health
If you develop flu-like symptoms when you return, you should see a seek medical attention immediately
Inform the health care provider who sees you, if you have been travelling to areas affected with Swine flu such as Mexico, California and Texas. (Details)
Usually include symptoms similar to season influenza (flu) including:
- headache, chills and cough followed by fever, loss of appetite, muscle aches and fatigue, runny nose, sneezing, watery eyes and throat irritation.
- Nausea, vomiting and diarrhea may occur in adults as well as in children.
- In more severe cases, or in people with chronic conditions, complications such as pneumonia may develop.
It is likely that most of people, especially those who do not have regular contact with pigs, do not have immunity to swine influenza viruses that can prevent the virus infection. If a swine virus establishes efficient human-to human transmission, it can cause an influenza pandemic. The impact of a pandemic caused by such a virus is difficult to predict: it depends on virulence of the virus, existing immunity among people, cross protection by antibodies acquired from seasonal influenza infection and host factors.
To diagnose swine influenza A infection, a respiratory specimen would generally need to be collected within the first 4 to 5 days of illness (when an infected person is most likely to be shedding virus). However, some persons, especially children, may shed virus for 10 days or longer. Identification as a swine flu influenza A virus requires sending the specimen to CDC for laboratory testing.
There are four different antiviral drugs that are licensed for use in the US for the treatment of influenza: amantadine, rimantadine, oseltamivir and zanamivir.
While most swine influenza viruses have been susceptible to all four drugs, the most recent swine influenza viruses isolated from humans are resistant to amantadine and rimantadine. At this time, CDC recommends the use of oseltamivir or zanamivir for the treatment and/or prevention of infection with swine influenza viruses.
The Hsw1N1 virus seen through a colorized transmission electron micrograph.
The Hsw1N1 virus causes Swine Influenza (swine flu) which is a respiratory disease of pigs caused by type A influenza that regularly results in outbreaks of influenza among pigs. Swine flu viruses do not normally infect humans. However, sporadic human infections with swine flu have occurred including the current outbreaks in Mexico and USA.
A/H1N1 influenza like human illness in Mexico and the USA: OIE statement