The origins of this new strain remain unknown. One theory is that Asian and European strains traveled to Mexico in migratory birds or in people, then combined with North American strains in Mexican pig factory farms before jumping over to farm workers.
Originating in Mexico this time, swine flu has caused more than 100 deaths there and moved to the US, where more than a dozen children in New York are found to have caught it after a visit to Mexico. There are reports also coming in from Spain and even as far off as New Zealand now.
Unconfirmed or suspected cases
The US declared a public health emergency on Sunday as a precautionary measure. A top official at the Centers for Disease Control and Prevention, or CDC, said she feared there would be deaths in the US as the new strain of flu spreads.
Mexican health officials have said that the original disease vector of the virus may have been flies multiplying in manure lagoons of pig farms near the town of Perote in Veracruz. The new strain is called H1N1, a subtype of the species influenza A virus.
What has triggered the panic is the knowledge that a variant of H1N1 was responsible for the Spanish flu pandemic that killed some 50 million to 100 million people worldwide over about a year in 1918 and 1919. Swine flu is characterized by a sudden fever, muscle ache, sore throat and dry cough. Victims of the new strain have also suffered more vomiting and diarrhea than is usual with the flu.
The anti-flu drugs Tamiflu and Relenza are said to be effective against the swine flu, so US authorities ordered the release of 25% of the national emergency stockpile of the drugs. They also recommended that local authorities should plan for possible school closures and that anyone with such symptoms should stay at home to reduce the possibility of causing the illness to spread.
Influenza A
Swine influenza is known to be caused by influenza A subtypes H1N1, H1N2, H3N1, H3N2, and H2N3.
In swine, three influenza A virus subtypes (H1N1, H3N2, and H1N2) are circulating throughout the world. In the United States, the H1N1 subtype was exclusively prevalent among swine populations before 1998; however, since late August 1998, H3N2 subtypes have been isolated from pigs. As of 2004, H3N2 virus isolates in US swine and turkey stocks were triple reassortants, containing genes from human (HA, NA, and PB1), swine (NS, NP, and M), and avian (PB2 and PA) lineages.
Interaction with H5N1
Avian influenza virus H3N2 is endemic in pigs in China and has been detected in pigs in Vietnam, increasing fears of the emergence of new variant strains. Health experts say pigs can carry human influenza viruses, which can combine (i.e. exchange homologous genome sub-units by genetic reassortment) with H5N1, passing genes and mutating into a form which can pass easily among humans. H3N2 evolved from H2N2 by antigenic shift.[10] In August 2004, researchers in China found H5N1 in pigs.
Nature magazine reported that Chairul Nidom, a virologist at Airlangga University's tropical disease center in Surabaya, East Java, conducted an independent research study in 2005. He tested the blood of 10 apparently healthy pigs housed near poultry farms in West Java where avian flu had broken out. 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.
Signs and symptoms
According to the Centers for Disease Control and Prevention (CDC), in humans the symptoms of swine flu are similar to those of influenza and of influenza-like illness in general. Symptoms include fever, cough, sore throat, body aches, headache, chills and fatigue. A few more patients than usual have also reported diarrhea and vomiting.
Because these symptoms are not specific to swine flu, a differential diagnosis of probable swine flu requires not only symptoms but also a high likelihood of swine flu due to the person's recent history. For example, during the 2009 swine flu outbreak in the United States, CDC advised physicians to "consider swine influenza infection in the differential diagnosis of patients with acute febrile respiratory illness who have either been in contact with persons with confirmed swine flu, or who were in one of the five U.S. states that have reported swine flu cases or in Mexico during the 7 days preceding their illness onset. A diagnosis of confirmed swine flu requires laboratory testing of a respiratory sample (a simple nose and throat swab).
Pathophysiology
Swine flu in humans
People who work with poultry and swine, especially people with intense exposures, are at increased risk of zoonotic infection with influenza virus endemic in these animals, and constitute a population of human hosts in which zoonosis and reassortment can co-occur. Transmission of influenza from swine to humans who work with swine was documented in a small surveillance study performed in 2004 at the University of Iowa. This study among others forms the basis of a recommendation that people whose jobs involve handling poultry and swine be the focus of increased public health surveillance. The 2009 swine flu outbreak is an apparent reassortment of several strains of influenza A virus subtype H1N1, including a strain endemic in humans and two strains endemic in pigs, as well as an avian influenza.
The CDC reports that the symptoms and transmission of the swine flu from human to human is much like that of seasonal flu. Common symptoms include fever, lethargy, lack of appetite and coughing, while runny nose, sore throat, nausea, vomiting and diarrhea have also been reported.It is believed to be spread between humans through coughing or sneezing of infected people and touching something with the virus on it and then touching their own nose or mouth. Swine flu cannot be spread by pork products, since the virus is not transmitted through food. The swine flu in humans is most contagious during the first five days of the illness although some people, most commonly children, can remain contagious for up to ten days. Diagnosis can be made by sending a specimen, collected during the first five days, to the CDC for analysis.
The swine flu is susceptible to four drugs licensed in the United States, amantadine, rimantadine, oseltamivir and zanamivir, however, for the 2009 outbreak it is recommended it be treated under medical advice only with oseltamivir and zanamivir to avoid drug resistance. The vaccine for the human seasonal H1N1 flu does not protect against the swine H1N1 flu, even if the virus strains are the same specific variety, as they are antigenically very different.
Prevention
Recommendations to prevent infection by the virus consist of the standard personal precautions against influenza. This includes frequent washing of hands with soap and water or with alcohol-based hand sanitizers, especially after being out in public. People should avoid touching their mouth, nose or eyes with their hands unless they've washed their hands. If people do cough, they should either cough into a tissue and throw it in the garbage immediately, cough into their elbow, or, if they cough in their hand, they should wash their hands immediately.[26] Vaccines that are effective against the current strain are being developed[27].
Safe Care Campaign reports that hand transmission is one way that germs are carried, not only from one area to another (for instance, a contaminated surface to your nose or mouth, but also from one person to another as when shaking hands). When attending to a patient, it is imperative to wash and/or sanitize hands, not only prior to touching them but afterwards as well.
Veterinary vaccines
Swine influenza has become a greater problem in recent decades as the evolution of the virus has resulted in inconsistent responses to traditional vaccines. Standard commercial swine flu vaccines are effective in controlling the infection when the virus strains match enough to have significant cross-protection, and custom (autogenous) vaccines made from the specific viruses isolated are created and used in the more difficult cases.[28][29]Treatment
The CDC recommends the use of Tamiflu (oseltamivir) or Relenza (zanamivir) for the treatment and/or prevention of infection with swine influenza viruses. The virus isolates that have been tested from the US and Mexico are however resistant to amantadine and rimantadine. If a person gets sick, antiviral drugs can make the illness milder and make the patient feel better faster. They may also prevent serious flu complications. For treatment, antiviral drugs work best if started soon after getting sick (within 2 days of symptoms).
Source : TOI, Wikipedia, Mayo Clinic Websites
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