Swine flu, or influenza, is caused by type A influenza and normally attacks the respiratory systems of pigs. This respiratory disease can reach epidemic proportions in pig populations. Though infection rates can be very high, mortality rates are not. Influenza can strike pig populations any time during the year, but just like the virus in humans, late fall and winter are the most active months. It was 1930 when the first case of swine flu virus (an influenza type A H1N1 virus) was identified in pigs.
How many varieties of Swine Flu are there?
Influenza viruses are constantly changing, and swine flu is no different, and pigs are susceptible to more than just this one variety. Human and avian can also attack pig populations, and when this happens, the virus can go through reassortment (a mixing of genetic material), forming new, combined strains of the virus. Through the years, several types of swine flu have been identified. Currently, the four major influenza type A subtypes found in pigs have been identified: H1N1, H1N2, H3N2, and H3N1. The most prevalent form of swine flu seen in recent years is H1N1.
Swine Flu in Humans
Cases of humans contracting swine flu:
Generally, the swine flu virus does not affect humans, but occasionally, humans in close contact with infected swine (those in the swine industry and others who have incidental contact) have fallen ill with the virus. There have been several documented instances of swine flu infected humans spreading the virus to others. The state of Wisconsin experienced these circumstances in 1988. A local swine flu outbreak in pigs spread to several human infections, but the outbreak did not reach very far and remained manageable. Evidence suggested that the virus spread from one person to healthcare professionals who had close contact with that patient.
Is swine flu in humans common?
No. The CDC receives reports of an isolated case of the swine flu virus approximately once every year or two in the US.
Symptoms of swine flu in humans
Much like the more common seasonal influenza virus, swine flu symptoms include fever, coughing, lack of appetite, and lethargy. Other symptoms occasionally include runny nose, vomiting, diarrhea, nausea, and sore throat.
Can swine flu be transmitted by eating pork?
Swine flu is transmitted by direct contact with an infected animal or person and cannot be contracted from food. Pork and pork products do not carry the virus, and as long as the meat is cooked properly (cooked to an internal temperature of 160°), any virus (including swine flu) and bacteria is killed.
How does the virus spread?
Swine flu and other strains of influenza is spread by direct contact and can be transmitted from pigs to humans, or humans to pigs. For a human to become infected by a pig, they have to be in close proximity to infected pigs – spending time in pig barns or in units housing pigs during exhibits, etc.). Humans transmit the virus to other humans in the same ways they transmit most influenza: coughing, sneezing, or any exchange of bodily fluids by touching the nose or mouth after coming in contact with an infected person.
In 1988, a pregnant woman, aged 32 and in good health, was hospitalized with pneumonia. Eight days later, she died. Tests revealed that H1N1 was present in her system. The woman visited a swine exhibit at a county fair just four days before becoming ill. Testing later showed that 1-3 of the health care professional who had contact with the woman developed flu-like symptoms and showed antibody evidence of swine influenza infection.
When tested, the pigs from the exhibit showed a strong incidence of the virus. In studies conducted after this unfortunate death, swine exhibitors showed a 76% rate of infection, but none were found to be seriously ill.
How are human infections of swine flu diagnosed?
For a swine influenza A diagnosis, the patient must submit a respiratory specimen in the first four to five days after being infected (the period when viral shedding is most likely). This shedding can take more than 10 days in some people, especially children. For a final diagnosis of swine flu influenza A virus, the specimen must be sent to the CDC for testing.
What medications are used to treat human swine flu infection?
In the US, four antiviral drugs are licensed for the treatment of influenza: amantadine, oseltamivir, rimantadine, and zanamivir. In recent cases of swine flu in humans, amantadine and rimantadine have been ineffective as treatments, with the virus showing resistance to the drugs. For the time being, the CDC is recommending oseltamivir or zanamivir to treat and prevent the occurrence of swine flu.
1976 swine flu outbreak at Fort Dix
An isolated case of swine flu at Fort Dix in New Jersey in 1976 is one of the most well known instances of swine influenza A outbreak. Four soldiers from a basic training unit were determined to have pneumonia stemming from infection from the virus. One soldier died from the infection and many more were hospitalized. All the patients were healthy previous to the outbreak. Within the closed environment of the training unit, transmission of the virus was limited to those with continual, close contact and very little interaction with others. The virus circulated among the group for a few weeks and then disappeared. The original source of the virus was never discovered. A sample of the virus taken from a soldier at Fort Dix was named A/New Jersey/76 (Hsw1N1). The outbreak cause widespread panic and urgent calls for nationwide vaccinations.
Are H1N1 swine flu and human H1N1 virus the same?
Human H1N1 and swine H1N1 are antigenically different, so immunizations for human, seasonal influenza will have no effect in warding off swine flu.
Pigs with Swine Flu
How do pigs spread swine flu?
Close contact and the sharing of contaminated items among pig populations is widely believed to be the way the virus spreads from infected to uninfected pigs. Some herds of pigs have continual swine flu infections circulating among the animals, and even herds vaccinated against the virus will have an occasional outbreak, though some will only have mild symptoms or show no symptoms at all.
Symptoms for swine flu in pigs
Signs that a pig may be infected with swine flu include sudden fever, coughing or barking, depression, difficulty breathing, sneezing, a discharge from the nose/eyes, lack of hunger, inflammation and redness of the eyes.
Is swine flu in pigs common?
US Pork Producers routinely deal with outbreaks of H1N1 and H3N2, as the virus frequently reaches endemic proportions in the industry. Late fall and winter are the most active months for the virus as it thrives in colder weather. Introducing new pigs into healthy herds can also cause outbreaks. The US isn’t the only country dealing with swine flu H1N1, however. Worldwide, 25 percent of pig populations exhibit virus antibodies. Studies in the United States show that 30 percent of pigs carry antibody evidence of having the disease at some time. This percentage goes up in the north-central portions of the US, showing 51 percent of the pig population displaying swine flu H1N1 antibodies. At this time, there is no reliable way to determine if pigs showing viral antibodies of H1N1 got the antibodies from vaccination or infection.
The H1N1 swine virus in pigs goes back to at least 1930, but the H3N2 variety was not detected in the US until 1998. The swine flu H3N2 and human H3N2 are very similar, and infection by humans was the initial cause for the spread of the disease among pigs.
While it is fairly common in pigs, infection of swine flu H1N1 in humans is very rare.
Can I get a vaccine?
Pigs can be vaccinated against swine flu, but there is no vaccine for humans. A vaccine for seasonal influenza will like give some protections against swine H3N2, but can do nothing to prevent swine H1N1.