Influenza A virus subtype H1N1
Influenza A (H1N1) virus is the subtype of influenza A virus that was the most common cause of human influenza (flu) in 2009. Some strains of H1N1 are endemic in humans and cause a small fraction of all influenza-like illness and a small fraction of all seasonal influenza. H1N1 strains caused a small percentage of all human flu infections in 2004–2005.1 Other strains of H1N1 are endemic in pigs (swine influenza) and in birds (avian influenza).
In June 2009, the World Health Organization declared the new strain of swine-origin H1N1 as a pandemic. This strain is often called swine flu by the public media. This novel virus spread worldwide and had caused about 17,000 deaths by the start of 2010. On August 10, 2010, the World Health Organization declared the H1N1 influenza pandemic over, saying worldwide flu activity had returned to typical seasonal patterns.2
On 26 April 2011, an H1N1 pandemic preparedness alert was issued by the World Health Organization (WHO) for the Americas.3
Swine influenza (also called swine flu, or pig flu) is an infection by any one of several types of swine influenza virus. Swine influenza virus (SIV) is any strain of the influenza family of viruses that is endemic in pigs. As of 2009, the known SIV strains include influenza C and the subtypes of influenza A known as H1N1, H1N2, H3N1, H3N2, and H2N3.
Swine influenza virus is common throughout pig populations worldwide. Transmission of the virus from pigs to humans is not common and does not always lead to human influenza, often resulting only in the production of antibodies in the blood. If transmission does cause human influenza, it is called zoonotic swine flu. People with regular exposure to pigs are at increased risk of swine flu infection. The meat of an infected animal poses no risk of infection when properly cooked.
Pigs experimentally infected with the strain of swine flu that is causing the current human pandemic showed clinical signs of flu within four days, and the virus spread to other uninfected pigs housed with the infected ones.5
During the mid-20th century, identification of influenza subtypes became possible, allowing accurate diagnosis of transmission to humans. Since then, only 50 such transmissions have been confirmed. These strains of swine flu rarely pass from human to human. Symptoms of zoonotic swine flu in humans are similar to those of influenza and of influenza-like illness in general, namely chills, fever, sore throat, muscle pains, severe headache, coughing, weakness, and general discomfort. The recommended time of isolation is about five days.
The Spanish flu, also known as la grippe, La Gripe Española, or La Pesadilla, was an unusually severe and deadly strain of avian influenza, a viral infectious disease, that killed some 50 to 100 million people worldwide over about a year in 1918 and 1919. It is thought to be one of the most deadly pandemics in human history.
The 1918 flu caused an unusual number of deaths, possibly due to it causing a cytokine storm in the body.67 (The current H5N1 bird flu, also an Influenza A virus, has a similar effect.)8 The Spanish flu virus infected lung cells, leading to overstimulation of the immune system via release of cytokines into the lung tissue. This leads to extensive leukocyte migration towards the lungs, causing destruction of lung tissue and secretion of liquid into the organ. This makes it difficult for the patient to breathe. In contrast to other pandemics, which mostly kill the old and the very young, the 1918 pandemic killed unusual numbers of young adults, which may have been due to their healthy immune systems mounting a too-strong and damaging response to the infection.9
The term "Spanish" flu was coined because Spain was at the time the only European country where the press were printing reports of the outbreak, which had killed thousands in the armies fighting World War I. Other countries suppressed the news in order to protect morale.10
In 1976, a novel swine influenza A (H1N1) caused severe respiratory illness in 13 soldiers with 1 death at Fort Dix, New Jersey. The virus was detected only from January 19 to February 9 and did not spread beyond Fort Dix.11 Retrospective serologic testing subsequently demonstrated that up to 230 soldiers had been infected with the novel virus, which was a H1N1 strain. The cause of the outbreak is still unknown and no exposure to pigs was identified.12
The 1977–1978 Russian flu epidemic was caused by strain Influenza A/USSR/90/77 (H1N1). It infected mostly children and young adults under 23 because a similar strain was prevalent in 1947–57, causing most adults to have substantial immunity. Because of a striking similarity in the viral RNA of both strains – one which is unlikely to appear in nature due to antigenic drift – it is being speculated that the later outbreak was due to a laboratory incident in Russia or Northern China, though this is being denied by scientists in those countries.131415 The virus was included in the 1978–1979 influenza vaccine.16171819
||The examples and perspective in this section may not represent a worldwide view of the subject. (May 2012)|
In the 2009 flu pandemic, the virus isolated from patients in the United States was 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."20 This new strain appears to be a result of reassortment of human influenza and swine influenza viruses, in all four different strains of subtype H1N1.
Preliminary genetic characterization found that the hemagglutinin (HA) gene was similar to that of swine flu viruses present in U.S. pigs since 1999, but the neuraminidase (NA) and matrix protein (M) genes resembled versions present in European swine flu isolates. The six genes from American swine flu are themselves mixtures of swine flu, bird flu, and human flu viruses.21 While viruses with this genetic makeup had not previously been found to be circulating in humans or pigs, there is no formal national surveillance system to determine what viruses are circulating in pigs in the U.S.22
In April 2009, an outbreak of influenza-like illness occurred in Mexico and the USA; the CDC reported seven cases of novel A/H1N1 influenza. By April 24 it became clear that the outbreak of ILI in Mexico and the confirmed cases of novel influenza A in the southwest US were related and WHO issued a health advisory on the outbreak of "influenza-like illness in the United States and Mexico".23 The disease then spread very rapidly, with the number of confirmed cases rising to 2,099 by May 7, despite aggressive measures taken by the Mexican government to curb the spread of the disease.24
On October 25, 2009 U.S. President Barack Obama officially declared H1N1 a national emergency26 Despite President Obama's concern, a Fairleigh Dickinson University PublicMind poll found in October 2009 that an overwhelming majority of New Jerseyans (74%) were not very worried or not at all worried about contracting the H1N1 flu virus.27 However, the President’s declaration caused many U.S. employers to take actions to help stem the spread of the swine flu and to accommodate employees and / or workflow which may be impacted by an outbreak.28
A study conducted in coordination with the University of Michigan Health Service is scheduled for publication in the December 2009 American Journal of Roentgenology warning that H1N1 flu can cause pulmonary embolism, surmised as a leading cause of death in this current pandemic. The study authors suggest physician evaluation via contrast enhanced CT scans for the presence of pulmonary emboli when caring for patients diagnosed with respiratory complications from a "severe" case of the H1N1 flu.29
March 21, 2010 worldwide update by the U.N.'s World Health Organization (WHO) states that "213 countries and overseas territories/communities have reported laboratory confirmed cases of pandemic influenza H1N1 2009, including at least 16,931 deaths."30
As of May 30, 2010 worldwide update by World Health Organization(WHO) more than 214 countries and overseas territories or communities have reported laboratory confirmed cases of pandemic influenza H1N1 2009, including over 18,138 deaths.31
The research team of Andrew Miller MD showed pregnant patients are at increased risk.32 It has been suggested that pregnant women and certain populations such as native North Americans have a greater likelihood of developing a T helper type 2 response to H1N1 influenza which may be responsible for the systemic inflammatory response syndrome that causes pulmonary edema and death.33
Pregnant women who contract H1N1 infection are recommended to receive antiviral therapy with either oseltamivir (which is the preferred medication) or zanamivir.34 Both amantidine and rimantidine have been found to be teratogenic and embryotoxic when given at high doses in animal studies.34
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- "Influenza Summary Update 20, 2004–2005 Season". FluView: A Weekly Influenza Surveilance Report. Centers for Disease Control and Prevention.
- Roos R (10 August 2010). "WHO says H1N1 pandemic is over". CIDRAP. Center for Infectious Disease Research and Policy, University of Minnesota.
- Recombinomics- H1N1 WHO Alert 2011 "WHO Issues H1N1 Pandemic Alert".
- "Humans May Give Swine Flu To Pigs In New Twist To Pandemic". Sciencedaily.com. 2009-07-10. Retrieved 2010-10-16.
- Kobasa D, Jones SM, Shinya K, et al (January 2007). "Aberrant innate immune response in lethal infection of macaques with the 1918 influenza virus". Nature 445 (7125): 319–23. doi:10.1038/nature05495. PMID 17230189.
- Kash JC, Tumpey TM, Proll SC, et al (October 2006). "Genomic analysis of increased host immune and cell death responses induced by 1918 influenza virus". Nature 443 (7111): 578–81. doi:10.1038/nature05181. PMC 2615558. PMID 17006449.
- Cheung CY, Poon LL, Lau AS, et al (December 2002). "Induction of proinflammatory cytokines in human macrophages by influenza A (H5N1) viruses: a mechanism for the unusual severity of human disease?". Lancet 360 (9348): 1831–7. doi:10.1016/S0140-6736(02)11772-7. PMID 12480361.
- Palese P (December 2004). "Influenza: old and new threats". Nat. Med. 10 (12 Suppl): S82–7. doi:10.1038/nm1141. PMID 15577936.
- Barry, John M. (2004). The Great Influenza: The Epic Story of the Greatest Plague in History. Viking Penguin. ISBN 0-670-89473-7.
- Gaydos JC, Top FH, Hodder RA, Russell PK (January 2006). "Swine influenza a outbreak, Fort Dix, New Jersey, 1976". Emerging Infect. Dis. 12 (1): 23–8. PMID 16494712.
- "Pandemic H1N1 2009 Influenza". CIDRAP. Center for Infectious Disease Research & Policy, University of Minnesota. Retrieved 2011-07-30.
- "1977 Russian Flu Pandemic". GlobalSecurity.org. Retrieved 22 December 2011.
- "Origin of current influenza H1N1 virus". virology blog. 2 March 2009. Retrieved 22 December 2011.
- "New Strain May Edge Out Seasonal Flu Bugs". NPR. 4 May 2009. Retrieved 22 December 2011.
- "Interactive health timeline box 1977: Russian flu scare". CNN.
- "Invasion from the Steppes". Time magazine. February 20, 1978.
- "Pandemic Influenza: Recent Pandemic Flu Scares". Global Security.
- "Russian flu confirmed in Alaska". State of Alaska Epidemiology Bulletin (9). April 21, 1978.
- "Deadly new flu virus in US and Mexico may go pandemic". New Scientist. 2009-04-26. Retrieved 2009-04-26.
- Susan Watts (2009-04-25). "Experts concerned about potential flu pandemic". BBC.
- Centers for Disease Control and Prevention (CDC) (April 2009). "Swine influenza A (H1N1) infection in two children—Southern California, March–April 2009". MMWR Morb. Mortal. Wkly. Rep. 58 (15): 400–2. PMID 19390508.
- "Influenza-like illness in the United States and Mexico". Disease Outbreak News. World Health Organization. 2009-04-24. Retrieved 2010-10-16.
- "Influenza A(H1N1) — update 19". Disease Outbreak News. World Health Organization. 2009-05-07. Retrieved 2010-10-16.
- Blippitt (2009-06-11). "H1N1 Pandemic – It's Official". N/A.
- "Obama declares swine flu a national emergency". The Daily Herald. 2009. Retrieved 2009-10-26.
- "The Arrival of H1N1 Influenza: Legal Considerations and Practical Suggestions for Employers". The National Law Review. Davis Wright Tremaine, LLP. 2009-11-02. Retrieved 2011-11-03.
- Mollura DJ, Asnis DS, Crupi RS, et al. (December 2009). "Imaging Findings in a Fatal Case of Pandemic Swine-Origin Influenza A (H1N1)". AJR Am J Roentgenol 193 (6): 1500–3. doi:10.2214/AJR.09.3365. PMC 2788497. PMID 19933640.
- "Situation updates – Pandemic (H1N1) 2009". World Health Organization. Retrieved 2010-10-16.
- "Pandemic (H1N1) 2009 – update 103". Disease Outbreak News. World Health Organization. 2010-06-04. Retrieved 2010-10-16.
- "H1N1 Pandemic Flu Hits Pregnant Women Hard". Businessweek.com. 2010-05-24. Retrieved 2010-10-16.
- McAlister VC (October 2009). "H1N1-related SIRS?". CMAJ 181 (9): 616–7. doi:10.1503/cmaj.109-2028. PMC 2764762. PMID 19858268.
- Health Care Guideline: Routine Prenatal Care. Fourteenth Edition. By the Institute for Clinical Systems Improvement. July 2010.
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- European Commission – Public Health EU Coordination on Pandemic (H1N1) 2009.
- Health-EU Portal EU work to prepare a global response to influenza A(H1N1).
- Influenza Research Database Database of influenza genomic sequences and related information.
- Centers For Disease Control and Prevention H1N1 Flu (Swine Flu).
- American Medical Association Physician Resources: Swine Flu
- Consultant Magazine H1N1 (Swine Flu) Center
- Pandemic Influenza: A Guide to Recent Institute of Medicine Studies and Workshops A collection of research papers and summaries of workshops by the Institute of Medicine on major policy issues related to pandemic influenza and other infectious disease threats.
- The Swine Flu Affair: Decision-Making on a Slippery Disease Report commissioned by the Department of Health, Education and Welfare, written by Richard Neustadt and Harvey V. Fineberg. An examination of what happened during and after the 1976 swine flu outbreak and lessons to help cope with similar situations in the future.
- Shreeve, J. (29 January 2006). "Why Revive a Deadly Flu Virus?". New York Times. Six-page human-interest story on the recreation of the deadly 1918 H1N1 flu virus
- "1918 flu virus's secrets revealed". BBC News. Results from analyzing a recreated strain.
- Noymer, A. (September 2005). "Some information on TB and the 1918 flu". Data from Noymer A, Garenne M (2000). "The 1918 influenza epidemic's effects on sex differentials in mortality in the United States". Popul Dev Rev 26 (3): 565–81. doi:10.1111/j.1728-4457.2000.00565.x. PMC 2740912. PMID 19530360.
- Oral history by 1918 pandemic survivor
- Ludwig S, Haustein A, Kaleta EF, Scholtissek C (July 1994). "Recent influenza A (H1N1) infections of pigs and turkeys in northern Europe". Virology 202 (1): 281–6. doi:10.1006/viro.1994.1344. PMID 8009840.
- Centers for Disease Control (CDC) (February 1987). "Influenza A(H1N1) associated with mild illness in a nursing home–Maine". MMWR Morb. Mortal. Wkly. Rep. 36 (4): 57–9. PMID 3100930.
- Lederberg J (February 2001). "H1N1-influenza as Lazarus: Genomic resurrection from the tomb of an unknown". Proc. Natl. Acad. Sci. U.S.A. 98 (5): 2115–6. doi:10.1073/pnas.051000798. PMC 33382. PMID 11226198.
- H1N1 Registry (ESICM – European Society of Intensive Care Medicine)