H5N1 Avian Influenza: History, Transmission, and Pandemic Risk

Introduction and Historical Background

Much like other communicable diseases, the H5N1 avian influenza virus — also known as bird flu — has a long history steeped in exploration, discovery, and revelation, dating back more than one hundred years to 1878 in Italy, where poultry farmers were struck with an epidemic then called "Fowl Plague." Some fifty years later, this type of avian flu virus appeared in the United States, either transmitted through immigrants from Italy and elsewhere in Europe or through the importing of virus-infected birds such as chickens from Italy and the greater Mediterranean area ("History of Avian Flu," Internet). In 1955, "Fowl Plague" was identified as the transmitter for this type of influenza, which generally affects all domesticated animals and especially birds. Technically, this type of flu is known as Highly Pathogenic Avian Influenza A virus and belongs to a subtype known as H5 ("History of Avian Flu," Internet).

Within the last ten years or so, the H5N1 flu virus has managed to spread to all regions of the world, particularly to Asian nations such as China, Japan, and South Korea, and to European nations such as Germany, Belgium, and the Netherlands, where a serious outbreak occurred in 2003. The H5N1 virus has also been reported in Central and South America, Mexico, the Middle East, and even Australia. This type of influenza holds the potential to greatly affect not only a country's population but also its economy by devastating poultry industries, which have often been forced to slaughter "millions of chickens, geese and turkeys to prevent further transmission" of the virus ("History of Avian Flu," Internet).

Global Spread and Economic Impact

The H5N1 virus has been responsible for a number of serious outbreaks in recent years, especially in Asia, where the poultry industry serves tens of millions of people on a daily basis. Although transmission of this flu subtype from animals to humans is relatively rare compared to other influenza strains, the World Health Organization is concerned "about the avian virus's potential to swap genes with a common flu virus," thereby creating a deadly and potentially untreatable illness that could spread globally in the form of a pandemic ("History of Avian Flu," Internet).

Transmission, Symptoms, and Pathogenesis

The H5N1 influenza virus is generally transmitted in two basic ways: first, by inhaling infected droplets from a virus carrier — whether an animal, bird, or human — which has been shown to be the most common mode of transmission; and second, by direct physical contact with infected droplets through the environment or human-to-human contact. Once exposed, the virus quickly infects the upper respiratory system, the sinuses, or both areas simultaneously, with an incubation period ranging from two days up to eight days or longer, depending on the degree of exposure and the mode of transmission (Beigel, et al., 1376).

Regarding symptoms, an infected person will first experience a high fever and disturbances linked to the lower respiratory tract, much like symptoms associated with more common types of flu. Along with these, there may also be vomiting, diarrhea, severe abdominal pain, and bleeding from the nose and gums, although these symptoms are relatively rare. Because of varying immune system responses to the H5N1 virus, some individuals may experience little discomfort and may report only a headache or infrequent diarrhea.

In relation to the pathogenesis and physical structure of the H5N1 influenza virus, Megan Talkington describes it as being composed of what is known as cleavable hemagglutinin — a type of antibody that agglutinates human red blood cells and is heterologous (47). The virus also contains a polymerase basic protein 2, which assists with replication, and a substitution in "nonstructural protein 1 that confers increased resistance to inhibition by interferons" and other biological factors (Beigel, et al., 1378). The viral replication process is currently under active exploration by researchers and geneticists. What is known is that replication is quite lengthy, ranging from six days to as long as sixteen days, and that the virus typically replicates most rapidly in the sinuses rather than in the lower respiratory tract (Beigel, et al., 1378).

Conclusion

Genetic sequencing of the virus has revealed a resistance to two of the most popular and widely-used antiviral medications, along with the possibility that the remaining antiviral medications may soon become ineffective ("Avian Influenza," Internet). The H5N1 influenza virus therefore holds the potential to trigger some form of future pandemic, in which millions of people could die, particularly children under the age of fifteen and the elderly.