Swine Flu, Swine Influenza Pandemic Support Forum

Swine influenza (also swine flu) refers to influenza caused by any virus of the family Orthomyxoviridae, that is endemic to pig (swine) populations. Strains endemic in swine are called swine influenza virus (SIV), and all known strains of SIV are classified as Influenzavirus A (common) or Influenzavirus C (rare).[1] Influenzavirus B has not been reported in swine. All three clades, Influenzavirus A, B, and C, are endemic in humans.

People who work with poultry and swine, especially people with intense exposures, are at risk of infection from these animals if the animals carry a strain that is also able to infect humans. SIV can mutate into a form that allows it to pass from human to human. The strain responsible for the 2009 swine flu outbreak is believed to have undergone this mutation.[2]

In humans, the symptoms of swine flu are similar to those of influenza and of influenza-like illness in general.

Classification
SIV strains isolated to date have been classified either as Influenzavirus C or one of the various subtypes of the genus Influenzavirus A.[3]


Influenza A
Swine influenza is known to be caused by influenza A subtypes H1N1,[4] H1N2,[4] H3N1,[5] H3N2,[4] and H2N3.[6]

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.[7]


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.[8] Health experts[who?] 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.[9] H3N2 evolved from H2N2 by antigenic shift.[10] In August 2004, researchers in China found H5N1 in pigs.[11]

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.[12][13]


Signs and Symptoms

Main symptoms of swine flu in humans.[14]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.[15]

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."[16] A diagnosis of confirmed swine flu requires laboratory testing of a respiratory sample (a simple nose and throat swab).[16]


Pathophysiology

Influenza viruses bind through hemagglutinin onto sialic acid sugars on the surfaces of epithelial cells; typically in the nose, throat and lungs of mammals and intestines of birds (Stage 1 in infection figure).[17]


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.[18] 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.[19] 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.[18] 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.[20]

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.[21] 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.[22] Swine flu cannot be spread by pork products, since the virus is not transmitted through food.[22] 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.[23]

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.[24] 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.[25]


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].


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]

Present vaccination strategies for SIV control and prevention in swine farms, typically include the use of one of several bivalent SIV vaccines commercially available in the United States. Of the 97 recent H3N2 isolates examined, only 41 isolates had strong serologic cross-reactions with antiserum to three commercial SIV vaccines. Since the protective ability of influenza vaccines depends primarily on the closeness of the match between the vaccine virus and the epidemic virus, the presence of nonreactive H3N2 SIV variants suggests that current commercial vaccines might not effectively protect pigs from infection with a majority of H3N2 viruses.[30][31]



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.[32] 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).




Epidemiology

Outbreaks in swine

2007 Philippine outbreak

On August 20, 2007 Department of Agriculture officers investigated the outbreak of swine flu in Nueva Ecija and Central Luzon, Philippines. The mortality rate is less than 10% for swine flu, unless there are complications like hog cholera. On July 27, 2007, the Philippine National Meat Inspection Service (NMIS) raised a hog cholera "red alert" warning over Metro Manila and 5 regions of Luzon after the disease spread to backyard pig farms in Bulacan and Pampanga, even if these tested negative for the swine flu virus.[33][34]



Outbreaks in humans

Swine flu has been reported numerous times as a zoonosis in humans, usually with limited distribution, rarely with a widespread distribution. The 1918 flu pandemic in humans was associated with H1N1,[35] thus may reflect a zoonosis either from swine to humans or from humans to swine. Evidence available from that time is not sufficient to resolve this question. The "Spanish" influenza pandemic of 1918–19 infected one third of the world's population (or around 500 million persons at that time) and caused around 50 million deaths.[35]


1976 U.S. outbreak

On February 5, 1976, an army recruit at Fort Dix said he felt tired and weak. He died the next day and four of his fellow soldiers were later hospitalized. Two weeks after his death, health officials announced that swine flu was the cause of death and that this strain of flu appeared to be closely related to the strain involved in the 1918 flu pandemic. Alarmed public-health officials decided that action must be taken to head off another major pandemic, and they urged President Gerald Ford that every person in the U.S. be vaccinated for the disease.[36]


However, the vaccination program was plagued by delays and public relations problems. But on Oct. 1, 1976, the immunization program began and by Oct. 11, approximately 40 million people, or about 24% of the population, had received swine flu immunizations. That same day, three senior citizens died soon after receiving their swine flu shots and there was a media outcry linking the deaths to the immunizations, despite not having any positive proof. According to science writer Patrick Di Justo, however, by the time the truth was known - that the deaths were not proven to be related to the vaccine - it was too late. "The government had long feared mass panic about swine flu -- now they feared mass panic about the swine flu vaccinations." This became a strong setback to the program.[37]

There were reports of Guillain-Barré syndrome, a paralyzing neuromuscular disorder, affecting some people who had received swine flu immunizations. As a result, Di Justo writes that "the public refused to trust a government-operated health program that killed old people and crippled young people." In total, less than 33 percent of the population had been immunized by the end of 1976. The National Influenza Immunization Program was effectively halted on Dec. 16.

Overall, about 500 cases of Guillain-Barré syndrome (GBS), resulting in death from severe pulmonary complications for 25 people, which, according to Dr. P. Haber, were probably caused by an immunopathological reaction to the 1976 vaccine. Other influenza vaccines have not been linked to GBS, though caution is advised for certain individuals, particularly those with a history of GBS.[38][39]






2009 swine flu outbreak

The new strain of influenza involved in the 2009 swine flu outbreak strain is a reassortment of several strains of influenza A virus subtype H1N1 that are, separately, endemic in humans and in swine. Preliminary genetic characterization found that the hemagglutinin (HA) gene was similar to that of swine flu viruses present in United States pigs since 1999, but the neuraminidase (NA) and matrix protein (M) genes resembled versions present in European swine flu isolates. Viruses with this genetic makeup had not previously been found to be circulating in humans or pigs, but there is no formal national surveillance system to determine what viruses are circulating in pigs in the United States.[40]


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.[41]


The earliest known human influenza A virus subtype H1N1 case was at a Mexican pig farm whose nearby neighbors had been complaining about the manure smell and flies.[42]


Edgar Hernandez, 4, was suffering from ordinary influenza but laboratory testing has since shown that he had contracted human influenza A virus subtype H1N1. The boy went on to make a full recovery.[43]


The Mexican health agency acknowledged that the original disease vector of the virus may have been flies multiplying in manure lagoons of pig farms near Perote, Veracruz, owned by Granjas Carroll,[44] a subsidiary of Smithfield Foods.[45]

Dr. Anne Schuchat, interim Deputy Director for CDC Science and Public Health, said that the American 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, and swine influenza virus typically found in Asia and Europe – "an unusually mongrelised mix of genetic sequences."[46] Pigs have been shown to act as a potential "mixing vessel" in which reassortment can occur between flu viruses of several species.[47][48] This new strain appears to be a result of reassortment of human influenza and swine influenza viruses, presumably due to superinfection in an individual human. Influenza viruses readily undergo reassortment because their genome is split between eight pieces of RNA (see Orthomyxoviridae).

The influenza A virus subtype H1N1 can adapt and spread more efficiently than previously known H1N1 strains. Moreover, co-infection of H1N1 swine flu and Oseltamivir resistant H1N1 season flu can lead to acquisition of H274Y by the swine flu via recombination or reassortment. Swine H1N1 with human H1 and N1 have been reported. Moreover, the swine flu can also infect swine and acquire more polymorphisms that could lead to increased virulence.

The 1918 pandemic strain has polymorphism from swine and human H1N1 in all eight pieces of RNA gene segments. Similar swapping of polymorphism in human co-infected with season and swine H1N1 can lead to rapid evolution.[49]





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Further reading
Van Reeth K (2007). "Avian and swine influenza viruses: our current understanding of the zoonotic risk". Vet. Res. 38 (2): 243–60. doi:10.1051/vetres:2006062. PMID 17257572.
Hampson AW, Mackenzie JS (November 2006). "The influenza viruses". Med. J. Aust. 185 (10 Suppl): S39–43. PMID 17115950. http://www.mja.com.au/public/issues/185_10_201106/ham10884_fm.html.

Lipatov AS, Govorkova EA, Webby RJ, et al. (September 2004). "Influenza: emergence and control". J. Virol. 78 (17): 8951–9. doi:10.1128/JVI.78.17.8951-8959.2004. PMID 15308692.
Reid AH, Taubenberger JK (September 2003). "The origin of the 1918 pandemic influenza virus: a continuing enigma". J. Gen. Virol. 84 (Pt 9): 2285–92. PMID 12917448. http://vir.sgmjournals.org/cgi/pmidlookup?view=long&pmid=12917448.

Taubenberger JK, Reid AH, Janczewski TA, Fanning TG (December 2001). "Integrating historical, clinical and molecular genetic data in order to explain the origin and virulence of the 1918 Spanish influenza virus". Philos. Trans. R. Soc. Lond., B, Biol. Sci. 356 (1416): 1829–39. doi:10.1098/rstb.2001.1020. PMID 11779381.
Alexander DJ (October 1982). "Ecological aspects of influenza A viruses in animals and their relationship to human influenza: a review". J R Soc Med 75 (10): 799–811. PMID 6752410.
Winkler WG (October 1970). "Influenza in animals: its possible public health significance". J. Wildl. Dis. 6 (4): 239–42; discussion 247–8. PMID 16512120. http://www.jwildlifedis.org/cgi/pmidlookup?view=long&pmid=16512120.

de Jong JC, Smith DJ, Lapedes AS, et al. (April 2007). "Antigenic and genetic evolution of swine influenza A (H3N2) viruses in Europe". J. Virol. 81 (8): 4315–22. doi:10.1128/JVI.02458-06. PMID 17287258.
Taubenberger JK, Morens DM (2008). "The pathology of influenza virus infections". Annu Rev Pathol 3: 499–522. doi:10.1146/annurev.pathmechdis.3.121806.154316. PMID 18039138.

External links
Centers for Disease Control and Prevention (CDC) - Swine Flu
"Swine Flu Cases Without Swine Exposure" Center for Biosecurity of UPMC
Outbreak Alerts Latest news and videos on viral epidemics and pandemics
The ongoing challenge of swine flu presentation by Marie Gramer, D.V.M., Ph.D., veterinary diagnostician at the University of Minnesota Veterinary Diagnostic Laboratory.
The Swine Flu Affair: Decision-Making on a Slippery Disease Original 1978 U.S.A. Department of Health Education and Welfare review by Richard E. Neustadt and Harvey V Fineberg available from Louisiana State University Law Center Medical and Public Health Law Site.
Surface sanitation and interruption of influenza using NAV-CO2
The Swine Flu Episode and the Fog of Epidemics by Richard Krause in CDC's Emerging Infectious Diseases Journal Vol. 12, No. 1 January 2006 published December 20, 2005
SWINE INFLUENZA by Carol G. Woodlief of College of Veterinary Medicine at North Carolina State University Overview, symptoms in pigs, treatment for pigs
In California and Texas, 5 New Swine Flu Cases Washington Post, By Rob Stein (Staff Writer)
Swine Flu In Mexico And U.S. May Lead To Pandemic, WHO Says AHN, Mayur Pahilajani (Staff Writer)
News and information on the 2009 human swine flu outbreak
H1N1 Swine Flu cases tagged on Google Maps
World Health Organization (WHO): Swine influenza
MedWorm's Swine Flu RSS Newsfeed (compiled from thousands of authoritative medical and news feeds)
Survival Emergency and Communication Gear


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