The Avian Influenza Virus (also known as bird flu) is hosted by birds and infects several species of mammals. It was first identified in Serbia and Montenegro in the early 1900. The avian influenza virus subtypes that have been confirmed in humans ordered by the number of known human deaths, are: H1N1 caused Spanish flu, H2N2 caused Asian Flu, H3N2 caused Hong Kong Flu, H5N1, H7N7, H9N2, H7N2, H7N3.
Avian Influenza Viruses compose the Influenza virus a genus of the Orthomyxoviridae family and are negative sense, single-stranded, segmented RNA viruses. "There are 16 different HA (Hemmaglutinin) antigens (H1 to H16) and 9 different NA (Neuraminidase) antigens (N1 to N9) for influenza A. These subtypes differ because of changes in certain proteins on the surface of the influenza A virus (hemagglutinin [HA] and Neuraminidase [NA] proteins). Many different combinations of HA and NA proteins are possible. Each combination represents a different subtype. All known subtypes of Influenza A viruses can be found in birds.
Avian influenza virus spreads in the air and in manure and survives longer in cold weather. 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.
Avian Influenza Virus subtype H5N1 is a highly pathogenic form and was first identified in 1997 and have caused the death of 10 million birds. It is one of the rare viruses that have its genome in separate segments. The Hemmaglutinin 5 glycoprotein forms spikes at the surface of virions, mediating attachment to host cell sialoside receptors and subsequent entry by membrane fusion. The NA1 forms a knob structure on the surface of virus particles and catalyses their release from infected cells allowing virus spread. It has the potential for recombinants to form by interchange of gene segments if two different viruses infect the same cell. 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. As of November 1, 2005, 122 cases of infections in humans, resulting in 62 deaths, have been confirmed in Southeast Asia.
Avian Influenza in birds:
Infected birds shed influenza virus in their saliva, nasal secretions, and feces. Susceptible birds become infected when they have contact with contaminated secretions or excretions or with surfaces that are contaminated with secretions or excretions from infected birds. Domesticated birds may become infected with AviaAvian Influenza is an infection caused by Avian (bird) Influenza (flu) viruses. These influenza viruses occur naturally among birds. Wild birds worldwide carry the viruses in their intestines, but usually do not get sick from them. However, Avian Influenza is very contagious among birds and can make some domesticated birds, including chickens, ducks, and turkeys, very sick and kill them. n Influenza virus through direct contact with infected waterfowl or other infected poultry, or through contact with surfaces (such as dirt or cages) or materials (such as water or feed) that have been contaminated with the virus.
Infection with avian influenza viruses in domestic poultry causes two main forms of disease that are distinguished by low and high extremes of virulence. The “low pathogenic” form may go undetected and usually causes only mild symptoms (such as ruffled feathers and a drop in egg production). However, the “highly pathogenic” form spreads more rapidly through flocks of poultry. This form may cause disease that affects multiple internal organs and has a mortality rate that can reach 90-100% often within 48 hours.
Avian Influenza in humans:
In humans, avian flu viruses cause similar symptoms to other types of flu. These include fever, cough, sore throat, muscle aches, conjunctivitis and, in severe cases, severe breathing problems and pneumonia that may be fatal. The severity of the infection will depend to a large part on the state of the infected person's immune system and if the victim has been exposed to the strain before, and is therefore partially immune. In one case, a boy with H5N1 experienced diarrhea followed rapidly by a coma without developing respiratory or flu-like symptoms, suggesting non-standard symptoms.
The avian influenza subtypes that have been confirmed in humans, ordered by the number of known human deaths, are: H1N1 caused Spanish flu, H2N2 caused Asian Flu, H3N2 caused Hong Kong Flu, H5N1, H7N7, H9N2, H7N2, H7N3, H10N7.
All avian influenza (AI) viruses are type A influenza virus in the virus family of Orthomyxoviridae and all known strains of influenza A virus infect birds. Influenza virus 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, avian influenza viruses may fall into one of 2 pathotypes: low (LPAI) and high (HPAI) pathogenecity, based on their virulence in poultry populations. Avian influenza virus H5 and H7 strains are found in both "low pathogenic” or “high pathogenic” forms; influenza H9 virus has been identified only in a “low pathogenic” form.
It is feared that if a strain of avian influenza virus to which humans have not been previously exposed undergoes antigenic shift to the point where it can cross the species barrier from birds to humans, the new subtype created could be both highly contagious and highly lethal in humans. If a human infected with influenza virus also acquires H5N1, a mutant strain of bird flu that can be transmitted from human to human could form. Such a subtype could cause a global pandemic similar to the Spanish Flu that killed up to 50 million people in 1918.
H1N1
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 . A different variant exists in pig populations. Controversy arose in October, 2005, after the H1N1 genome was published in the journal, Science. Many fear that this information could be used for bioterrorism.
"When he compared the 1918 virus with today's human flu viruses, Dr. Taubenberger noticed that it had alterations in just 25 to 30 of the virus's 4,400 amino acids. Those few changes turned a bird virus into a killer that could spread from person to person."
H2N2
The Asian Flu was a pandemic outbreak of H2N2 avian influenza that originated in China in 1957, spread worldwide that same year during which a flu vaccine was developed, lasted until 1958 and caused between one and four million deaths.
H3N2
H3N2 evolved from H2N2 by antigenic shift and caused the Hong Kong Flu pandemic of 1968 and 1969 that killed up to 750,000. (Detailed chart of its evolution here.) "An early-onset, severe form of influenza A (H3N2) made headlines when it claimed the lives of several children in the United States in late 2003."
H5N1
H5N1 is a highly pathogenic form of avian influenza virus. Since 1997, outbreaks of H5N1 flu 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. Influenza A (H5N1) virus – also called “H5N1 virus” – is an influenza A virus subtype that occurs mainly in birds, is highly contagious among birds, and can be deadly to them. Outbreaks of avian influenza H5N1 occurred among poultry in eight countries in Asia (Cambodia, China, Indonesia, Japan, Laos, South Korea, Thailand, and Vietnam) during late 2003 and early 2004. At that time, more than 100 million birds in the affected countries either died from the disease or were killed in order to try to control the outbreaks. By March 2004, the outbreak was reported to be under control. Since late June 2004, however, new outbreaks of influenza H5N1 among poultry were reported by several countries in Asia (Cambodia, China [Tibet], Indonesia, Kazakhstan, Malaysia, Mongolia, Russia [Siberia], Thailand, and Vietnam). It is believed that these outbreaks are ongoing. Influenza H5N1 infection also has been reported among poultry in Turkey and Romania and among wild migratory birds in Croatia.
Human cases of influenza A (H5N1) infection have been reported in Cambodia, China, Indonesia, Thailand, and Vietnam. For the most current information about avian influenza and cumulative case numbers, see the World Health Organization (WHO) website at http://www.who.int/csr/disease/avian_influenza/en/. As of November 1, 2005, 122 cases of infections in humans, resulting in 62 deaths, have been confirmed outside of China. H5N1 virus does not usually infect people, but more than 130 human cases have been reported by the World Health Organization since January 2004. Most of these cases have occurred as a result of people having direct or close contact with infected poultry or contaminated surfaces; however, a few cases of human-to-human spread of H5N1 have occurred.
Of the few avian influenza viruses that have crossed the species barrier to infect humans, H5N1 has caused the largest number of detected cases of severe disease and death in humans. In the current outbreaks in Asia and Europe, more than half of those infected with the virus have died. Most cases have occurred in previously healthy children and young adults. However, it is possible that the only cases currently being reported are those in the most severely ill people, and that the full range of illness caused by the H5N1 virus has not yet been defined.
So far, the spread of H5N1 virus from person to person has been rare and has not continued beyond one person. Nonetheless, because all influenza viruses have the ability to change, scientists are concerned that H5N1 virus one day could be able to infect humans and spread easily from one person to another. Because these viruses do not commonly infect humans, there is little or no immune protection against them in the human population. If H5N1 virus were to gain the capacity to spread easily from person to person, an influenza pandemic (worldwide outbreak of disease) could begin. No one can predict when a pandemic might occur. However, experts from around the world are watching the H5N1 situation in Asia and Europe very closely and are preparing for the possibility that the virus may begin to spread more easily and widely from person to person.
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 was recorded.
H9N2
Low pathogenic avian influenza A (H9N2) infection was confirmed in 1999, in China and Hong Kong in two children, and in 2003 in Hong Kong in one child. All three fully recovered. CDC
H7N2
One person in New York in 2003 and one person in Virginia in 2002 were found to have serologic evidence of infection with H7N2. Both fully recovered.
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. "Symptoms included conjunctivitis and mild influenza like illness." CDC detailed analysis Both fully recovered.
H10N7
In 2004 in Egypt H10N7 is reported for the first time in humans. It caused illness in two infants in Egypt. One child’s father is a poultry merchant.
Prevention and treatment
Although avian influenz avirus in humans can be detected with standard influenza virus 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. 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 three laboratory .
Antiviral drugs such as oseltamivir, zanamivir and amantadine are sometimes effective in both preventing and treating the infection. Countries have been stockpiling olestamivir, but may shift towards zanamivir due to a November 2005 issue of JAMA, which reported oseltamivir resistant strains of avian flu in Vietnam.
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. The use of amantadine was approved by the Chinese Ministry of Agriculture. 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.
Osteopathic physicians used the lymphatic pump method during the 1917 influenza pandemic to increase the immune system's response. According to (Knott 2005), "osteopathic manipulative treatment (OMT) decreased the mortality rate from 5% to 0.25% among 100,000 patients."
There is some evidence that indicates that Kimchi and by extension Sauerkraut may be used to treat avian influenza in birds. There is currently no evidence of its effects on humans.
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 from the H5N1 type of avian influenza virus. One of the primary concerns is that the virus could quickly spread across countries as various birds follow their migration routes. 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.
(WHO) announced on November, 16, 2005 that an outbreak is most likely to hit the Hong Kong Special Administrative Region by mid-December of this year. "If it were to hit in a highly residential area like Tin Hau, it would be sure to spread like wildfire." Dr. N Column, Head of Epidemic Prevention announced.
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.
An Oseltamivir resistant H5N1 avian influenza virus was isolated from a Vietnamese girl in Feb. 2005.
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