Avian influenza
From Biocrawler, the free encyclopedia.
Avian influenza (also known as bird flu or avian flu) is a type of influenza virus that is hosted by birds, but may infect several species of mammals. It was first identified in Italy in the early 1900s and is now known to exist worldwide. Avian influenza viruses compose genus A of the Orthomyxoviridae family and are negative-stranded, segmented RNA viruses. A strain of the H5N1-type of avian influenza that emerged in 1997 has been identified as the most likely source of a future influenza pandemic.
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Infection
Strains of avian influenza may infect various type of animals, including birds, pigs, horses, seals, whales and humans. However, wild fowl act as natural asymptomatic carriers, spreading it to more susceptible domestic stocks. Avian influenza spreads in the air and in manure. It can also be transmitted by contaminated feed, water, equipment and clothing; however, there is no evidence that the virus can survive in well cooked meat.
The incubation period is 3 to 5 days. Symptoms in animals vary, but virulent strains can cause death within a few days.
Since January 2004, all known human cases of avian flu have occurred in Southeast Asia. There have been approximately 120 reported cases; approximately half of the patients in these cases have died. It has been determined in nearly all of these cases that contraction of the virus occurred from chickens.
Subtypes pathogenic to humans
All avian influenza (AI) viruses are type A influenza in the virus family of Orthomyxoviridae and all known subtypes of influenza A virus can infect birds. Influenza type A is subdivided into subtypes based on hemagglutinin (H) and neuraminidase (N) protein spikes from the central virus core. There are 16 H types, each with up to 9 N subtypes, yielding a potential for 144 different H and N combinations. In addition, all AI viruses fall into one of 2 pathotypes: low (LPAI) and high (HPAI) pathogenicity, based on their virulence in poultry populations.
It is feared that if the avian influenza virus undergoes antigenic shift to the point where it can cross the species barrier (e.g., from birds to humans), the new subtype created could be both highly contagious and highly lethal in humans. Such a subtype could cause a global pandemic similar to the Spanish Flu that killed up to 50 million people in 1918.
However, there are substantial genetic differences between the subtypes that typically infect both people and birds. Within subtypes of avian influenza viruses there also are different strains. Avian influenza H5 and H7 viruses can be found in both "low pathogenic” or “high pathogenic” forms depending on genetic features and the severity of the illness they cause in poultry; influenza H9 virus has been identified only in a “low pathogenic” form.
H1N1
Main article: H1N1
H1N1 was the first identified strain of Type A influenza. In early October 2005, researchers announced that they had successfully reconstructed the Spanish Flu virus. The gene sequence indicates that the 1918 epidemic was caused by H1N1, normally considered a strain of swine flu (which itself falls under avian influenza) that in this case passed directly from birds to humans. The reconstructed virus is very different from normal human viruses in that it infects lung cells which would normally be impervious to the virus [1] (http://news.yahoo.com/s/ap/20051006/ap_on_he_me/pandemic_flu;_ylt=ApmVvpKqjuQsYrD46ESjkZms0NUE;_ylu=X3oDMTA3b2NibDltBHNlYwM3MTY-).
H5N1
Main article: H5N1
H5N1 is a highly pathogenic form of avian influenza. Since 1997, outbreaks of H5N1 have caused the death or culling of tens of millions of birds. Over 100 people have been infected by H5N1, with a mortality rate of over 50%. H5N1 has been the focus of much concern amid warnings that the H5N1 strain will likely evolve into a form that causes a global human pandemic with a very high mortality rate.
Other strains
Since 1997 the H5N1, H7N2, H7N3, H7N7, and H9N2 have been confirmed in humans.
- H2N2
- Responsible for the Asian Flu pandemic of 1957 and 1958 that killed at least a million people worldwide.
- H3N2
- Evolved from H2N2 by antigenic shift and caused the Hong Kong Flu pandemic of 1968 and 1969 that killed up to 750,000. This was the least deadly pandemic of the twentieth century.
- H7N2
- Following an outbreak of H7N2 among poultry in 2002, 44 people were found infected in Virginia, United States.
- H7N3
- In North America, the presence of avian influenza strain H7N3 was confirmed at several poultry farms in British Columbia in February 2004. As of April 2004, 18 farms had been quarantined to halt the spread of the virus. Two cases of humans with avian influenza have been confirmed in that region.
- H7N7
- In 2003 in Netherlands 89 people were confirmed to have H7N7 influenza virus infection following an outbreak in poultry on several farms. One death has been recorded.
- H9N2
- The virus type has been documented only in low pathogenic form. Three infections in humans (China and Hong Kong) have been confirmed, all three patients recovered. In October 2005 an outbreak has been detected in the province of Tolima, central Colombia. No human infections have been reported.[2] (http://www.bloomberg.com/apps/news?pid=10000086&sid=as0Yp3nTrOos&refer=latin_america)
Prevention and treatment
Although avian influenza in humans can be detected with standard influenza tests, these tests have not always proved reliable. In March 2005, the World Health Organization announced that seven people from Vietnam who initially tested negative for bird flu were later found to have carried the virus. All seven have since recovered from the disease. Currently (6/05) the most reliable test (microneutralization) requires use of the live virus to interact with antibodies from the patient's blood; because live virus is required, for safety reasons the test can only be done in a level 3 laboratory [3] (http://www.canada.com/health/story.html?id=63cbe9ea-a151-4877-b1e1-aa522176ff6f).
Antiviral drugs are sometimes effective in both preventing and treating the disease, but no virus has ever been really cured in medical history. Vaccines, however, take at least four months to produce and must be prepared for each subtype.
Further, as a result of widespread use of the antiviral drug amantadine as a preventive or treatment for chickens in China starting in the late 1990s, some strains of the avian flu virus in Asia have developed drug resistance against amantadine [4] (http://www.washingtonpost.com/wp-dyn/content/article/2005/06/17/AR2005061701214.html). Chickens in China have received an estimated 2.6 billion doses of amantadine since early 2004. This use of amantadine for poultry goes against international livestock regulations, but China kept it secret until recently, in a manner reminiscent of the secrecy around the early spread of SARS.
Increasing virulence
In July 2004 researchers led by H. Deng of the Harbin Veterinary Research Institute, Harbin, China and Professor Robert Webster of the St Jude Children's Research Hospital, Memphis, Tennessee, reported results of experiments in which mice had been exposed to 21 isolates of confirmed H5N1 strains obtained from ducks in China between 1999 and 2002. They found "a clear temporal pattern of progressively increasing pathogenicity". [5] (http://www.pnas.org/cgi/content/abstract/0403212101v1) Results reported by Dr. Webster in July 2005 reveal further progression toward pathogenicity in mice and longer virus shedding by ducks.
As of July 2005, most human cases of avian influenza in East Asia have been attributed to consumption of diseased poultry. Person-to-person transmission has not been unequivocally confirmed in the outbreaks in East Asia.
In May 2005, the occurrence of Avian influenza in pigs in Indonesia was reported ("swine flu"). Along with the continuing pattern of virus circulation in poultry, the occurrence in swine raises the level of concern about the possible evolution of the virus into a strain capable of causing a global human influenza pandemic. Health experts say pigs can carry human influenza viruses, which can combine (i.e. exchange homologous genome sub-units by genetic reassortment.) with the avian virus, swap genes and mutate into a form which can pass easily among humans.
On August 3, 2005, the United Nations World Health Organization (WHO) said it was following closely reports from China that at least 38 people have died and more than 200 others have been made ill by a swine-borne disease (possible "pig flu" outbreak) in Sichuan province. Sichuan Province, where infections with Streptococcus suis have been detected in pigs in a concurrent outbreak, has one of the largest pig populations in China. The outbreak in humans has some unusual features and is being closely followed by the WHO. At that time, Chinese authorities say they have found no evidence of human-to-human transmission [6] (http://www.un.org/apps/news/story.asp?NewsID=15279&Cr=pig&Cr1=flu).
On September 29, 2005, David Nabarro, the newly appointed Senior United Nations System Coordinator for Avian and Human Influenza, warned the world that an outbreak of Avian influenza could kill 5 to 150 million people. Also, due to a bipartisan effort of the United States Senate, $4 billion dollars was appropriated to develop vaccines and treatments for Avian influenza.[7] (http://www.un.org/News/briefings/docs/2005/050929_Nabarro.doc.htm)
On October 14, 2005, European health officials confirmed what many had long feared -- the arrival of the H5N1 strain on Europe's doorstep. The European Commission said the bird flu outbreak in Turkey was indeed H5N1 and advised Europe to prepare for a pandemic. It has also been reported in Romania.
On October 17, 2005, a bird flu outbreak occurred in Chios, Greece. The mayor of Chios said a farmer on Oinousses who raised turkeys and chickens noted the previous week that some of his birds had died. Two state veterinarians were sent in to look at nine turkeys. They also took blood samples from some chickens. The mayor said a state lab in Athens confirmed that one of the nine samples proved positive. Authorities have yet to announce what measures they will be taking. The farmer was taken to a hospital for observation. [8] (http://edition.cnn.com/2005/HEALTH/conditions/10/17/birdflu.greece/index.html)
Symptoms
- See also: Influenza symptoms
In humans, it has been found that avian flu causes similar symptoms to other types of flu [9] (http://www.bupa.co.uk/health_information/html/health_news/270104avianflu.html):
- fever
- cough
- sore throat
- muscle aches
- conjunctivitis
- in severe cases of avian flu, it can cause severe breathing problems and pneumonia, and can be fatal.
In one case, a boy with H5N1 presented to the hospital with diarrhea followed rapidly by a coma without developing respiratory or flu-like symptoms.[10] (http://content.nejm.org/cgi/content/short/352/7/686)
Potential pandemic
Main article: influenza pandemic
The World Health Organization (WHO) has warned of a substantial risk of an influenza epidemic in the near future, most probably of the the H5N1 type of avian influenza. In response, countries have begun planning in anticipation of an outbreak. While short-term strategies to deal with an outbreak focus on limiting travel and culling and vaccinating poultry, long-term strategies require substantial changes in the lifestyles of the most at-risk populations.
The WHO divides a pandemic into six phases, ranging from minimal risk of an outbreak to full scale pandemic. Most health authorities categorize the situation as of 2005 at Phase 3, by which is meant that human infections of a new sub-type has occurred but there is little evidence of sustained human-to-human transmission.
See also
- The Spanish flu from 1918–19
- The Asian Flu from 1957–58
- The Hong Kong Flu from 1969–69
References
- Kuiken T et al (2004), Avian H5N1 Influenza in Cats, Science 2004 306: 241 (DOI:10.1126/science.1102287 (http://dx.doi.org/10.1126/science.1102287))
External links
General
- WHO Avian influenza frequently asked questions. (http://www.who.int/csr/disease/avian_influenza/avian_faqs/en)
- A guide to bird flu and its symptoms from BBC Health. (http://www.bbc.co.uk/health/conditions/birdflu1.shtml)
- Nature's special issue on avian flu. Welcome to this Web Focus on Avian Flu, containing news and scientific reports warning about the potential for a new human flu pandemic in the near future. (http://www.nature.com/nature/focus/avianflu/index.html)
- CDC Information about avian influenza, including recent outbreaks, the viruses, and the risk to human health. (http://www.cdc.gov/flu/avian/index.htm)
- FIC, flu in china & flu information center (bilingual, with forums). (http://www.flu.org.cn/)
- The Flu Wiki - to help local communities prepare for and perhaps cope with a possible influenza pandemic. (http://www.fluwikie.com/index.php?n=Main.HomePage)
- Information regarding Avian Influenza (Bird Flu) and the possiblity of Human Pandemic. (http://goldbamboo.com/pulse-1042005_SP1-2bird+flu.html)
- Using GIDEON to diagnose Avian Flu. (http://www.gideononline.com/case/avianflu.htm)
- Key Facts About Avian Influenza (Bird Flu) and Avian Influenza A (H5N1) Virus. (http://www.iwar.org.uk/news-archive/2005/03-18-4.htm)
- The Avian flu tag on the Connotea social bookmarking service provides updated references of news, reports, resources and scientific papers on avian flu and the risk of a pandemic (http://www.connotea.org/tag/AvianFlu)
- Pandemic Influenza Risk Communication: The Teachable Moment, by Sandman and Lanard (http://www.psandman.com/col/pandemic.htm)
- CIDRAP - Avian Influenza (an excellent collection of information; news links, lab confirmed count of cases, suggested reading, etc) (http://www.cidrap.umn.edu/cidrap/content/influenza/avianflu/)
News
- News on the disease from the US government. (http://usinfo.state.gov/gi/global_issues/bird_flu.html)
- Farmers 'key to bird-flu control' (http://www.cnn.com/2005/HEALTH/conditions/02/23/bird.flu.asia/)
- Bird flu experts warn of pandemic (http://news.bbc.co.uk/1/hi/world/asia-pacific/4647485.stm)
- Bird flu news (http://birdfluprotection.com/current_news/index.php) - Current News from many sources
- Emergency Measures Avian flu is on the rise in Vietnam and is now endemic in much of Asia. Can heightened vigilance keep it at bay? (http://www.time.com/time/asia/magazine/article/0,13673,501050207-1022651,00.html)
- United Nations begins ensure that there are effective local, national, regional and global preparations for a potential avian flu pandemic (http://www.un.org/News/briefings/docs/2005/050929_Nabarro.doc.htm)
- Experts Unlock Clues to Spread of 1918 Flu Virus (http://www.nytimes.com/2005/10/06/health/06flu.html?ex=1286251200&en=3f9a510cfd4c3d45&ei=5090) - The New York Times
- Avian influenza (http://www.newsxs.com/en/preset/398) - NewsXS newsfeed
- Bird Flu Headquarters (http://birdfluheadquarters.com) : Community based site monitoring news from all over the world; provides visitors with all news, commentary, information, resources; gives members the option of creating their own blog free.
Preparing
- Emergency Preparedness List (http://home.san.rr.com/earlybird/Emergency%20Kit.xls)
- Letter to raise public awareness, describing what to do now and when a pandemic occurs. (http://home.san.rr.com/earlybird/BF_PSA.pdf)
- H5N1 Avian Flu Virus Therapy - Conventional and Herbal Options (http://www.med-owl.com/health/H5N1-Virus-Therapy.html)
- "Ask Me About Bird Flu" shirts and other awareness products (http://www.cafepress.com/h5n1)
- Prepare Your Family For Bird Flu (http://www.prepare-for-bird-flu.com/)
- Avian Flu Preparedness Guide - from The Center for Technology and National Security Policy (http://www.ndu.edu/ctnsp/Bird_flu.htm)
Blogs
- Worldwide Disasters - Pandemics (http://www.worldwide-disasters.com/?cat=8)
- Avian Flu News (http://www.healthdiaries.com/news/infectiousdisease/archives/bird_flu/index.html)
- Avian Flu at Typepad: a blog with further links. (http://avianflu.typepad.com)
- EPIDEMIca: Coverage of the ongoing H5N1 outbreak in China, Vietnam and Thailand. (http://www.epidemi.ca)
- Vogelgrippe-News (http://www.vogelgrippe-virus.de) (ger.)
- Daily news on Avian Flu (http://www.lastinfoo.com/avian_flu_outbreak.phtml)
- Updated daily news digest on bird flu and the pandemic (http://influenzapandemic.blogspot.com)
- A blog on H5N1 (http://crofsblogs.typepad.com/h5n1/)
- H5N1 bird flu and migratory birds forum. (http://www.drmartinwilliams.com/index.php?option=com_simpleboard&Itemid=155&func=showcat&catid=7/)
- Bird Flu Forum (http://birdfluprotection.com/bird_flu_forum/viewforum.php?f=1)
- Agonist (http://discuss.agonist.org/yabbse/index.php?board=6)
- Curevents (http://www.curevents.com/vb/forumdisplay.php?f=40)
- Bird Flu Updates: blog with up-to-date news and informational links (http://www.bird-flu-updates.com)
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