Swine influenza

Pigs can have more than one type of flu at the same time. This means that viruses can mix genes and become a type of flu that could cause a pandemic.

Swine influenza virus is a virus that is common in pigs. This type of influenza virus can also infect humans and birds. Swine influenza virus is sometimes called SIV or swine flu.

Swine flu is common in pigs. Normally, it only infects people who have been in close contact with pigs. However, the disease can spread from one person to another.^[1] Swine flu can cause fever, disorientation (not being clear-headed), stiffness of the joints, vomiting, and loss of consciousness. Sometimes this ends in death.^[2] There are different types, or strains, of swine flu. They are called H1N1,^[3] H1N2,^[3] H3N1,^[4] H3N2,^[3] and H2N3.^[5]

Background

Military hospital during Spanish flu pandemic in 1918.

H1N1 came from the Spanish flu, which caused a pandemic in humans in 1918 and 1919.^[6]^[7] New viruses came from the Spanish flu. These viruses became common in pigs. Every once in a while, the viruses spread from pigs to humans. This has happened during the 20th century. (However, they happened at the same time as the flu epidemics that happen every year. Because of this, it is hard to tell the difference between 'normal' influenza and swine influenza.)^[6] Infections that spread from pigs to humans are rare. Scientists only know of 12 known cases in the United States since 2005.^[8]

It is very difficult to prevent the flu virus. This is because the virus changes all the time. If a person gets the flu, his body forms antibodies to fight that virus off if it happens again. But since the flu virus changes all the time, a person's antibodies may not recognize the virus the next time it happens, because it is different. The same thing happens with vaccines.

The changes in the flu virus can cause a flu pandemic. For example, the virus might only change a little bit in about two to three years. After about ten years, most people will have developed antibodies to fight these small changes. But if the virus then changes a lot, there can be a pandemic. Hundreds of millions of people suddenly realize that the antibodies they developed are useless.^[9] Even during the Spanish flu pandemic, the first wave of the disease was relatively mild, while the second wave was very deadly.^[7]

In 1957, an Asian flu pandemic infected about 45 million Americans and killed 70,000. Eleven years later, from 1968 to 1969, the Hong Kong flu pandemic infected 50 million Americans and caused 33,000 deaths. It also cost about $3.9 billion. In 1976, about 500 soldiers became infected with swine flu over a few weeks. However, by the end of the month, investigators found that the virus had "mysteriously disappeared", and there were no more signs of swine flu.^[7] There were a small number of isolated (far-apart) cases around the U.S. These were in people who were thought to have caught the virus from pigs.

Scientists fear the swine flu virus might mutate, or change, into a pandemic as deadly as the 1918/1919 pandemic. They watched the outbreak in 2009, and made plans about what to do if a global pandemic breaks out.

Symptoms

The main symptoms of the swine influenza is much the same as regular influenza. Symptoms include vomiting, nausea, runny nose, loss of appetite, lethargy (feeling tired), chills, fever, body aches, sore throat, coughing, diarrhea, and stomach ache.

Where swine influenza is found

The bird flu virus H3N2 is endemic in pigs in China. It has been found in pigs in Vietnam. Specialists also think that this might lead to new variations of the influenza virus.^[10] Pigs can carry human influenza viruses. These viruses can combine in new ways, and exchange certain genes with H5N1. Through mutation, this would create a form of the virus that can pass easily among humans.^[11] H3N2 evolved from H2N2 by antigenic shift.^[12] In August 2004, researchers in China found H5N1 in pigs.^[13]

In 2005 it was discovered that H5N1 could be infecting up to half of the pig population in some areas of Indonesia, but without showing symptoms. Chairul Nidom, a virologist at Airlangga University's tropical disease center in Surabaya, East Java, did some independent research: he tested the blood of 10 apparently healthy pigs housed near poultry farms in West Java where avian flu had broken out, Nature reported. Five of the pig samples contained the H5N1 virus. The Indonesian government has since found similar results in the same region. Additional tests of 150 pigs outside the area were negative.^[14]^[15]

Swine Flu in Humans

Electron microscope image of the N1H1 virus. The viruses are 80–120 nanometres in diameter.^[16]

The Centers for Disease Control and Prevention (CDC), a United States government agency, reports that the symptoms and transmission of the swine flu from human to human is much like seasonal flu. Usually, the symptoms are fever, lethargy (feeling tired), lack of appetite and coughing. Some people with swine flu also have reported runny nose, sore throat, nausea, vomiting and diarrhoea.^[17] It is believed to be spread between humans when an infected person coughs or sneezes and then touches something. Another person then might touch the same thing with the virus on it and then touch their own nose or mouth.^[18] The swine flu in humans is most contagious during the first five days of the illness although some people, most commonly children, can be contagious for up to ten days. Diagnosis can be made by sending a specimen (sample), collected during the first five days, for analysis.^[19]

The Swine Flu is susceptible to four licensed drugs in the United States, amantadine, rimantadine, oseltamivir and zanamivir. However, for the 2009 outbreak, it was recommended it be treated with oseltamivir and zanamivir.^[20] The vaccine for the human seasonal flu does not protect against the swine flu.

Veterinary swine flu vaccine

The virus has evolved. This has made Swine influenza a bigger problem, mainly because traditional vaccines against influenza do not always work against Swine influenza. There are special vaccines against Swine influenza, but they only work if the virus strain is similar to some extent. In the cases more difficult to treat, special vaccines are produced. These are very similar, as they are made to match the specific virus strain.^[21]^[22]

Present vaccination strategies for SIV control and prevention in swine farms use vaccines commercially available in the United States. The protective ability of influenza vaccines depends primarily on the closeness of the match between the vaccine virus and the epidemic virus.^[23]^[24] The current vaccine against the seasonal influenza strain H1N1 is thought unlikely to provide protection.^[25] The director of CDC's National Center for Immunization and Respiratory Diseases said that the United States' cases were found to be made up of genetic elements from four different flu viruses—North American swine influenza, North American avian influenza, human influenza A virus subtype H1N1, and swine influenza virus typically found in Asia and Europe. On two cases, a complete genome sequence had been obtained. She said that the virus is resistant to amantadine and rimantadine, but susceptible to oseltamivir (Tamiflu) and zanamivir (Relenza).^[26]^[27]^[28]

2009 outbreak (Swine flu)

Map of the swine flu deaths Confirmed cases, people died Confirmed cases, no deaths Unconfirmed or suspected cases No cases or no data

A new strain of swine influenza A called H1N1 was responsible for the swine flu outbreak in 2009 in humans. It came from a combination of several strains of influenza in humans and influenza in birds and swine influenza. Tests were done. Testers found that the hemagglutinin gene was similar to that of swine flu viruses that had already been found in pigs in the United States since 1999, but the neuraminidase and matrix protein genes resembled versions in European swine. Viruses like this had not been found in humans or pigs before. There is no program to monitor what viruses are circulating in pigs in the United States, however it began in Mexico, North America.^[29]

Legacy in WHO guidelines

In 2009, the government of Egypt ordered over 300,000 pigs killed to prevent the spread of H1N1, even though experts said the pigs were not going to spread H1N1 anyway. Most of the pigs' owners were not paid for their dead pigs.^[30]^[31]

In 2015, the World Health Organization made itself some rules for naming viruses: No official name is allowed to refer to a place, person or animal. This is to prevent stigma, or blame. The WHO rules list "swine flu" as an example of what not to do when naming a virus or disease.^[32]^[33]

Swine Influenza Media

Main symptoms of swine flu in humans
In this video, Dr. Joe Bresee, with CDC's Influenza Division, describes the symptoms of swine flu and warning signs to look for that indicate the need for urgent medical attention. See also: See this video with subtitles on YouTube
H1N1 enveloped virus with outer lipid membrane having glycoprotein "spikes"
Thermal scanning of passengers arriving at Singapore Changi airport
Illustration of antigenic shift
Thermal imaging camera and screen, photographed in an airport terminal in Greece – thermal imaging can detect elevated body temperature, one of the signs of the virus H1N1 (swine influenza).
U.S. President Gerald Ford receives a swine flu vaccination