Health is a blessing, 130 new claims for a healthy life

Author: Xue Dong
Publisher:
Publish Date: 2006-07-20
Features: Avian Influenza: A Sudden Calamity Threatening Human Survival
In early 2005, avian influenza cases continued to appear in Southeast Asia, prompting countries worldwide to consider how to effectively monitor and prevent a potential pandemic. Over the past century, several outbreaks of viral influenza have posed significant threats to humanity. In just one instance in 1918, hundreds of millions of people lost their lives globally. Through long-term evolution, the most dangerous influenza viruses to humans have evolved from the H1 lineage in 1918 to the H5 lineage. Historically, humans have never had contact with the H5 strain of avian influenza virus. As a result, people have no immunity to this virus at all. If the H5 strain mutates and combines with influenza viruses circulating in the human population, it could spread rapidly among humans, potentially triggering a pandemic of unprecedented scale. Some predict that the next pandemic could cause millions of deaths. To date, avian influenza viruses have not posed a large-scale threat to humans. This is mainly because there is no direct evidence to suggest that the H5 strain can spread from person to person. Currently, researchers in China and many other countries around the world are closely monitoring the H5 strain of avian influenza virus. What exactly are the experts watching? Beyond monitoring, what preventive measures do humans have against the potential threat of H5 avian influenza?
The Spread of H5 Avian Influenza Virus in Domestic Poultry
In nature, avian influenza viruses primarily infect the digestive tracts of wild birds and spread over wide geographic areas. Some bird species, especially aquatic birds, are frequent hosts of avian influenza viruses. While the virus itself may not cause disease, it continuously spreads to other wild or domestic birds through feces and secretions. In domestic poultry, the H5 avian influenza virus behaves less kindly than it does in wild birds, often causing varying degrees of infection symptoms. Weaker strains of the virus can make domestic poultry lethargic and reduce egg production, while stronger strains can kill entire clutches or even entire flocks. Whenever domestic poultry are infected, researchers analyze the characteristics of the virus to determine the likelihood of it causing disease in humans. Taking the United States as an example, there have been 16 outbreaks of viral infections affecting domestic poultry since 1997.
The Spread of Avian Influenza Virus Across Species
Avian influenza viruses can devastate a country's poultry industry, but so far, they have largely remained confined to birds, following the "avian" part of their name, without widespread transmission to other animal species. This is because the genetic composition of the virus determines its host range. However, there have been exceptions. In the past, avian influenza viruses have infected humans, cats, leopards, and even flies. The genetic makeup of the virus also limits its spread within other species. Nevertheless, when the virus "crosses the line" to infect other species, it represents a step toward spreading beyond birds into other animal populations, marking the beginning of transmission from bird to animal and then animal to animal.
From a genetic perspective, influenza viruses are composed of eight independent gene segments. This relatively independent genetic structure creates conditions for viruses to exchange genetic material, leading to the formation of new viruses. The emergence of new viruses can occur through two mechanisms: zoonotic evolution and using animals as intermediaries. Zoonotic evolution refers to the simultaneous infection of a human by both avian influenza viruses and human influenza viruses. The two viruses then exchange genetic segments, evolving into a new virus capable of spreading among humans while retaining the surface protein characteristics of avian influenza. Using animals as intermediaries can begin when both human and avian influenza viruses infect an "intermediate host." If both viruses infect pigs, it is highly likely that they will exchange genetic segments and produce a new virus.
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