*H5N1 Or Avian Influenza*
Influenza A virus is a member of the family Orthomyxoviridae. It is enveloped, with a segmented, single-stranded RNA gene. (1) Commonly known as Avian Influenza or H5N1 it first came on the scene of our world consciousness in 1996. The first pathogenic strain was isolated from a farmed goose in the Guangdong Province in China. (10) To date there have been 387 confirmed human cases of H5N1 worldwide 245 of which were fatal (10). H5N1 has garnered attention because it has a wide geographical distribution in species of birds, and the number and severity of human infections has not been seen before. The concern is when the virus mutates to a strain transmitted readily among humans, and unless there is a dramatic decrease in the pathogenicity of the virus, the result will be a pandemic with mortality rates not seen since the 1918 pandemic. (1) In 1918 - 1919 the world faced the H1N1 flu pandemic, commonly called the Spanish Flu, it infected 20 to 40 million people and has been cited as the most devastating epidemic in recorded world history. (5) H5N1 has all of the requirements to be the next global pandemic. What we know about H5N1, its effects, how it is transmitted, prevention, and how to test for it, are all important considerations on how we are going to fight it.
There are two main types of the H5N1 virus. A low pathogenic strain commonly referred to as LPAI H5N1, and a high pathogenic strain referred to as HPAI H5N1or Asian H5N1. Asian H5N1 is the strain that spreads rapidly and has a high death rate in birds and has been able to infect people. So far the incidence of the HPAI has been outside the United States. However the LPAI strain occurs naturally in wild birds and can spread to domestic birds. This strain is common, has mild symptoms, and doesn't pose a significant threat to human health. (6) Although, the LPAI strain has been discovered in the United States this report will concentrate on the HPAI strain.
Infected birds shed the H5N1 virus through secretions in their saliva, nose and feces. New birds get infected when they have contact with contaminated surfaces or excretions from infected birds. Domestic cats and dogs have been infected by the ingestion of raw infected poultry parts. (3) Domestic birds also have been infected from dirt, cages, water or feed that has been contaminated by the virus. In birds the H5N1 virus has a mortality rate of between 90 - 100% often within 48 hours. (2)
In 1997 the first cases of human infections with the avian influenza were reported in Hong Kong. Most people who have contracted the H5N1 virus have been in direct contact with infected poultry. (10) In 2004 the first case of human to human transmission was suspected but not confirmed. Then in January of 2005 was the first confirmed case of human to human transmission in Thailand. (9) Symptoms of H5N1 in humans range from typical flu symptoms (e.g., fever, cough, sore throat, and muscle aches) to eye infections, pneumonia, severe respiratory diseases (such as acute respiratory distress), and other severe and Life-threatening complications. (2) there was a fatal case in Viet Nam in Feb 2004 that had diarrhea and encephalitis but normal chest X rays. (10) H5N1 has a high mortality rate over 50 %. (1)
How would one know if they were infected with H5N1? Historically a diagnosis cannot be made by symptoms alone, so a lab test is required. Usually a swab is taken from the nose or throat during the first few days of the illness. Testing for H5N1 is done by growing the virus out or a molecular test will be performed. (2) This process can take up to two weeks for results. Commercial antigen testing was tried with little success resulting in only 4 positive tests in 11 cases that were later confirmed with the slower methods. (4) Currently a real time reverse transcriptase polymerase chain reaction test is the best method for initial diagnosis providing a result within 4 -6 hours.(5)
Treatment for H5N1 consists of administration of current antiviral agents. Depending on the particular strain this can be helpful. Some strains have mutated into antiviral resistant strains. Amantadine and rimantadine have been ineffective on clade 1 viruses but effective on clade 2. There is no known cure for all strains of H5N1. Early treatment with oseltamivir seems to suggest that it improves survivability but high level resistance has been demonstrated in some patients. (5)
Prevention is the best option where avian influenza is concerned. Avian influenza A is inactivated by soap, detergent, alcohols, and chlorination.
There are two vaccines that are in clinical trials an inactivated vaccine and an attenuated vaccine. Two doses are required to show raised antibody levels. The durability of the antibody response is limited.(5) These are the vaccines that many countries are stockpiling in case a pandemic breaks out but ongoing research is still working on a more effective and cost effective solution.
In conclusion, H5N1 is not yet in a form that poses a great danger of global catastrophe. It does however, have the possibility of being the next global pandemic virus with just a few mutations. It mutates easily and is becoming resistant to the antiviral agents we currently have. It has a high mortality rate, and is easily transmitted among birds. Some strains have shown a human to human transmission within a family, which is a small step from being easily transmitted between unrelated people. If a global pandemic occurs it will probably be spread by domestic and wild birds. It can be transmitted by fecal matter, direct contact, or contact with a contaminated surface. Measures are being taken to mitigate the danger in the form of research and the formulation of vaccines.
1. American Society for Microbiology (2006 December 18 Updated 2008 March 06) Sentinel Laboratory Guidelines for Suspected Agents of Bioterrorism and Emerging Infectious Diseases Avian Influenza A H5N1
2. Center for Disease Control (1997, May 07) Key Facts About Avian Influenza (Bird Flu) and Avian Influenza A (H5N1) Virus
3. Center For Disease Control (Volume 12, Number 11 - November 2006) Fatal Avian Influenza A H5N1 in a Dog. http://www.cdc.gov/ncidod/EID/vol12no11/06-0542.htm
4. New England Journal of Medicine (2005, September 29) Avian Influenza A (H5N1) Infection in Humans
5. New England Journal of Medicine (2008 January 17) Update on Avian Influenza A (H5N1) Virus Infection in Humans
6. Stanford University, Molly Billings (1997, June) Modified RDS February, 2005. The Influenza Pandemic of 1918.
7. United States Department of Agriculture (2007, July 23). Avian Influenza Low Pathogenic H5N1 vs. Highly Pathogenic H5N1. http://www.usda.gov/wps/portal/usdahome?contentidonly=true&contentid=2006/08/0296.xml
8. University of Melbourne (2008, November 11). 1918 Spanish Flu Records Could Hold The Key To Solving Future Pandemics. http://uninews.unimelb.edu.au/view.php?articleID=5550
9. World Health Organization (2008, September 10). Cumulative Number of Confirmed Human Cases of Avian Influenza A/ (H5N1) Reported to WHO. http://www.who.int/csr/disease/avian_influenza/country/cases_table_2008_09_10/en/index.html
10. World Health Organization (2008, November 11). H5N1 avian influenza: Timeline of major events. http://www.who.int/csr/disease/avian_influenza/ai_timeline/en/index.html
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