Why Bird Flu is Seen as a Potential Health Risk to Humans

By:Jessica Deets

The Avian Flu, also known as the Asian Bird Flu or Influenza A (H5N1), is a zoological viral strain that has crossed the species barrier and is now threatening further mutation and a subsequent world pandemic.

Influenza A strains infect only avian and mammal species while influenza B and C strains infect only humans. Most human influenza strains encounter higher levels of immunity among the human population and are less virulent because they have been around for longer periods and world populations have developed necessary immunity.

Conversely, Influenza A (H5N1), after undergoing an antigenic shift (crossing the species barrier), presents an entirely new threat because the human population has no previous immunity or resistance to this flu. Strains that have mutated in this way, and become transmittable between humans, have been the cause of every previous flu epidemic or pandemic for the last 300 years. Researchers suggest that a if global pandemic of Influenza A (H5N1) mimicked the pandemic of 1918-1919, the death toll could reach between 150 and 300 million people.

Influenza A (H5N1) was discovered in 1996 thru an outbreak in the domestic poultry industry in Hong Kong. During 2003 and 2004 over 100 million birds died of the flu, or were culled to prevent spreading of the flu in eight Asian countries: Cambodia, China, Indonesia, Japan, Laos, South Korea, Thailand, and Vietnam. By the March of 2004 the flu was reportedly contained, but since June of that year the flu has spread through migrating flocks of wild fowl to Kazakhstan, Malaysia, Mongolia, Siberia, and Tibet, and is now suspected of being in flocks of migratory and domestic birds in Turkey, Romania, and Croatia.

The first fatality to a human from Influenza A (H5N1) was that of a 3 year old boy in 1997 in Hong Kong. Seventeen other infections were recorded during that first outbreak, 6 of which were fatal, all infections were contracted directly from fowl by people either working within the commercial poultry industry, or by visiting a retail stand where live poultry was sold. The initial outbreak prompted an territory-wide slaughter of over 1.5 million chickens, and though that outbreak stopped, the disease continued to spread to other places. Surveys conducted showed that direct exposure to live infected poultry approximately one week before illness symptoms was the only common occurrence among those infected, and is the associated means of inoculation.

Outbreaks spread to other countries with the evidentiary source of inoculation being exposure to poultry, but two cases in 2004, one in Thailand and the other in Vietnam, stand out as possible instances of human to human transmission.

In Thailand an 11 year old girl was admitted to the hospital with a fever, sore throat, and cough. Her cough worsened to respiratory distress and shock, and she was transferred to another hospital where she died the following day. Her mother, who lived and worked in another province, had come to care for her in the hospital. The mother was there with her daughter for approximately 16 to 18 hours during which she nursed and took care of her daughter, but did not use any prophylactic devices in the process.

After the child’s death, the mother went back to the child’s village for the funeral, and then back to the province she was living in. When she got home, the mother was admitted to the hospital because she became ill with fever and had difficulty breathing. Despite aggressive antibiotic treatment she died three days later of respiratory failure and Pneumonia. During the initial onset of the child’s illness, she was living with an aunt, her mother’s sister, and the initial care and nursing was preformed by this aunt, also unprotected. The aunt contracted muscle pain, fever, and chills on the same day that the girl’s mother became ill, and was admitted to her local hospital.

An investigating team suspected Avian Flu to be the cause of the aunt’s illness and treated with an aggressive combination of antiviral medications while taking isolation precautions. Within two weeks her condition improved and she was released. During the investigation for the possibility of Influenza A (H5N1), swabs were taken from the aunt, and the body of the mother, but not from the child as her body was cremated soon after death.

All test results came back positive for Influenza A (H5N1) after a specific reverse-transcriptase–polymerase-chain-reaction (RT-PCR) analysis and genetic sequencing. The aunt and child had culled infected chickens in household three or four days before the onset of the initial flu, and the child was probably inoculated there. However, the human to human transmission is suggested by the timing of the onset of the mother and aunts illnesses, as well as the fact that the mother came from another province and had no viable exposure to livestock or poultry in any form during the acceptable incubation period (4 to 18 days), while she did participate in unprotected nursing of her sick daughter. Human-to-human transmission is the only realistic source of infection.

The other instance of possible person-to-person transmission of Influenza A (H5N1) is found in South Vietnam. A nine-year-old girl was admitted to the hospital with a four day history of severe diarrhea, fever and drowsiness. Her consciousness quickly depleted, and she was soon comatose. Tests showed that she had swelling of the brain; she was treated with mannitol, but despite aggressive support including intubation and ventilation she died the following day. Acute encephalitis from unknown origin was recorded as the cause of death. They did not do an autopsy. Within two weeks her four-year-old brother came in with a two day history of similar symptoms including a headache, vomiting, and severe diarrhea. He was alert and awake at the time of admitting, but soon slipped into lesser consciousness and eventually coma. He was transferred to a bigger facility, and put on more aggressive support. Encephalitis, as well as respiratory failure was what took his life 12 hours after his transfer to that facility. Both children died within 7 days of the onset of symptoms, and both were in good general health up to that point. Rectal and throat swabs, as well as cerebrospinal fluid were taken from the boy for testing. The Influenza A (H5N1) virus was ultimately found in all of the samples, but much more heavily in the rectal sample, suggesting the GI tract to be the primary incubation area for this particular strain.

The children and parents lived in a one room house, and used a nearby canal for cleaning and cooking water. The girl also swam in the canal often. No other illness was reported among relatives or neighbors and no sick poultry or birds were found in the area, though all were culled. If the girl was infected by a virus found in the water during her swimming, the only explanation for her brother getting the disease is human to human transfer, as the water from the canal was treated before it was used in the home, and the brother didn’t swim. Also, the incubation period of 10 days fits with the spread of disease from person to person. Notable points in this case are that the Influenza A (H5N1) virus acted differently upon these two children than in other cases, effecting their nervous system, and not showing pronounced respiratory symptoms at inception.

These two instances represent the fears of the medical community and ultimately the social and political organizations of the world today. Influenza A (H5N1) mutated into a virulent airborne pathogen would create a pandemic such as the world has never experienced to date. Measures are already being taken to prepare for a shift in this direction. The world health organization is developing standardized protocol for hospitals to implement in the treatment of patients who are suspected or confirmed carriers of Influenza A (H5N1), such as isolated monitoring, diagnostic testing, and antiviral therapy.

To date, the drugs that have had the most immediate success are oseltamivir and zanamivir, and specified dosing charts are in the process of being developed, and amended as further research on emerging viral strains comes forward.

Antiviral drugs are being produced in more efficient ways and are being disseminated to the areas that need it most. Several vaccines are under development right now from older Influenza A strains, as well as from Influenza A (H5N1).

Science is working quickly to produce an economical prevention to this global threat, but is being hindered by minimal cooperation in the international arena. Researchers and analysts urge the need for powerful immediate collaboration on a threat so large that synergy is the only hope for global survival.

Copyright (c) 2006.

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Article keywords: avian flu, bird flu, H5N1

Article Source: http://www.articles2k.com

From expert author Jessica Deets with major contributions from Tacy Oberan. For more news and bird flu developments, see the website at http://www.BestFluInfo.com

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