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 issue 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.
Avian Influenza (Bird Flu)
Avian influenza, or �bird flu�, is a contagious disease of animals caused by viruses that normally infect only birds and, less commonly, pigs. Avian influenza viruses are highly species-specific, but have, on rare occasions, crossed the species barrier to infect humans.
In domestic poultry, infection with avian influenza viruses causes two main forms of disease. The so-called �low pathogenic� form commonly causes only mild symptoms (ruffled feathers, a drop in egg production) and may easily go undetected. The highly pathogenic form is far more dramatic. It spreads very rapidly through poultry flocks, causes disease affecting multiple internal organs, and has a mortality that can approach 100%, often within 48 hours.
Influenza A viruses have 16 H subtypes and 9 N subtypes. Only viruses of the H5 and H7 subtypes are known to cause the highly pathogenic form of the disease. On present understanding, H5 and H7 viruses may circulate and infect poultry flocks in their low pathogenic form. The viruses can then mutate, usually within a few months, into the highly pathogenic form. This is why the presence of an H5 or H7 virus in poultry is always cause for concern, even when the initial signs of infection are mild. Read more »
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Posted in medicalmatrix | February 13, 2010 | 
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Background
Influenza virus infection, one of the most common infectious diseases, is a highly contagious airborne disease that causes an acute febrile illness and results in variable degrees of systemic symptoms, ranging from mild fatigue to respiratory failure and death. These symptoms contribute to significant loss of workdays, human suffering, mortality, and significant morbidity. The 1918-1919 H1N1 type influenza pandemic killed an estimated 20-50 million persons, with 549,000 deaths in the United States alone.
Accurately diagnosing influenza A or B infection based solely on clinical criteria is difficult because of the overlapping symptoms caused by the various viruses associated with upper respiratory tract infection (URTI). In addition, several serious viruses, including adenoviruses, enteroviruses, and paramyxoviruses, may initially cause influenzalike symptoms. The early presentation of mild or moderate cases of flavivirus infections (eg, dengue) may initially mimic influenza. For example, some cases of West Nile fever acquired in New York in 1999 were clinically misdiagnosed as influenza.
Patients with influenza frequently present with various symptoms shared by many other viral infections. In the northern and southern hemispheres, these symptoms are more common in the winter months. As a result, during the winter, clinics and emergency department waiting rooms fill with patients who have influenza or other URTIs.
Pathophysiology
Influenza results from infection with 1 of 3 basic types of influenza virus—A, B, or C—which are classified within the family Orthomyxoviridae. These single-stranded RNA viruses are structurally and biologically similar but vary antigenically.
The RNA core consists of 8 gene segments surrounded by a coat of 10 (influenza A) or 11 (influenza B) proteins. Immunologically, the most significant surface proteins include hemagglutinin and neuraminidase. The viruses are typed based on these proteins. For example, influenza A subtype H3N2 expresses hemagglutinin 3 and neuraminidase 2.
The most common prevailing influenza A subtypes that infect humans are H1N1 and H3N2. Each year, the trivalent vaccine used worldwide contains A strains from H1N1 and H3N2, along with an influenza B strain.
Influenza virus infection occurs after transfer of respiratory secretions from an infected individual to a person who is immunologically susceptible. If not neutralized by secretory antibodies, the virus invades airway and respiratory tract cells. Once within host cells, cellular dysfunction and degeneration occur, along with viral replication and release of viral progeny. Systemic symptoms result from inflammatory mediators, similar to other viruses. The incubation period of influenza ranges from 18-72 hours.
Influenza A is generally more pathogenic than influenza B. Influenza A is a zoonotic infection, and more than 100 types of influenza A infect most species of birds, pigs, horses, dogs and seals. Indeed, the 1918 pandemic that resulted in millions of human deaths worldwide is believed to have originated from a virulent strain of H1N1 from pigs or birds. Recently, scientists obtained and sequenced the 1918 H1N1 strain from a frozen corpse found in Alaska. The virus was reconstructed at the Centers for Disease Control and Prevention (CDC) laboratory in Atlanta and was found to be highly lethal when tested in mice; the virus was also found to be lethal to chicken embryos. This unique N1 neuraminidase is being studied in order to provide better insight into the N1 found in H5N1, the type responsible for avian influenza (also known as bird flu). Read more »
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Clinical, B.
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