Avian Influenza a (H5N1) Avian

Avian Influenza a (H5N1)

Avian Influenza is a subtype of Influenza a, a member of the Orthomyxiviridae family, which can cause disease states in humans (CIDRAP, 2008). This virus can be transmitted through birds to humans. (CIDRAP, 2008). Historically, only the influenza a strains produced pandemics in the human population. This research will examine the etiology, origins, methods of transmission, symptoms, treatment, epidemiology, and other affect of the H5N1 virus on the human population.

To understand the impact of the H5N1 strain, it is important to understand how this strain relates to other viruses and influenza strains. The H5N1 virus is a subtype of influenza consisting of 16 different antigens (H1 to H16) (CIDRAP, 2008). There are also nine different NA antigens (N1 to N9) (CIDRAP, 2008). Influenza strains are classified according to their potential to produce a pandemic in the human population. Three types of strains exist, nonpandemic strains, potential pandemic strains, and animal pandemic strains. Currently, the H5 and H7 strains are of greatest concern to the human population as they can readily transmit throughout the human population (CIDRAP, 2008).

Avian Influenza, named for its affect on wild and domestic bird populations, is divided into two types. High pathogenic avian influenza (HPAI) is highly virulent, with death rates in affected flocks approaching 100%. Low pathogenic avian influenza (LPAI) rarely causes death, but can mutate in to HPAI strains (CIDRAP, 2008). The current strain of H5N1 proved to be an HPAI strain in domestic Asian birds. However, other forma of the H5N1 strain are less virulent and are classified as LPAI strains (CIDRAP, 2008). Both HPAI and LPAI strains can affect humans (HHS, 2005).

The H5N1 strain, as we currently know it, began in South-east Asian in mid-2003 (WHO, 2008). The disease proved tenacious, rapidly affecting Indonesia, Cambodia, China, Thailand, and the Laos. The disease resulted in the destruction of an estimated 150 million domestic birds (WHO, 2008). The list of infected Asian countries grew and now includes the Republic of Korea, Vietnam, Japan, and Malaysia, as well as those previously listed (WHO, 2008). Japan, the Republic of Korea, and Malaysia currently report to have the disease under control in bird populations (WHO, 2008).

The H5N1 virus is devastating in bird populations, but it is impact on human populations that is of most concern. The risk occurs when the disease passes from poultry to human hosts. The first recorded incident of and H5N1 outbreak in humans occurred in 1997, where it infected 18 people and killed six (WHO, 2008). In early 2003, the virus caused two infections and one death in Hong Kong (WHO, 2008). In most cases, infections in the human population occurred in rural areas where people keep small poultry flocks. In communities where poultry is an important farm commodity, families will often quickly kill or slaughter animals when they become sick. The slaughtering of animals is the most common form of transmission from birds to humans (WHO, 2008).

Since its onset, H5N1 has been reported in human populations in eastern Europe, the Middle East, and in Northern Africa (Salzberg, et al., 2007). A total of 251 confirmed cases have been found on a global basis, resulting in 148 deaths (Salzberg, et al., 2007). The total number of cases may not be cause for alarm, but the death rate among those that contracted the disease are of concern. These numbers suggest that if Avian flu were to enter the human population and begin to spread in pandemic form, it could be a highly virulent strain with a high associated death rate among its victims.

Of the key problems in the spread and treatment of bird flu is its similarity to many less virulent influenza strains. The most common symptoms are fever, sore throat, muscle aches, headache, lethargy, conjunctivitis, breathing problems and chest pains (Macnair, 2007). These symptoms are not significantly different from more common, less significant strains of flu. People will be less likely to recognize the severity of their illness and seek help until the symptoms become severe.

The focus of treatment of H5N1 is on prevention of its spread through the development of vaccinations. However, one cannot develop the vaccine before the outbreak occurs. From development to commercial production of the vaccine would take approximately three months after a pandemic has been declared (WHO, 2008). The vaccine developed must be matched exactly to the disease, or it will prove ineffective. The development of a vaccine that is not effective is a waste of money, resources, and will do nothing to help stop the spread of disease. This does not mean that a vaccine is useless, it will help to control and stop the pandemic once it is started. Without the development of a vaccine, the pandemic would have a more devastating effect on the human population. The disease would literally be able to spread unchecked on a global basis.

There are currently two drugs on the market that are effective against H5N1. They are both in the neuraminidase inhibitor class. Osletamivir (tamiflu) and zanamivir (Relenza) can reduce the severity and duration of seasonal influenza (WHO, 2008). These two drugs are effective, but their effectiveness is dependent upon several variables. They are most effective when administered within 48 hours of symptom onset (WHO, 2008). This can be problematic, as many people do not seek help until the symptoms are severe or have persisted over a considerable amount of time. These two drugs offer the greatest hope for the H5N1 virus, but there is still no guarantee that they will be effective against the pandemic strain.

The number of humans affected by avian flu is dwarfed by the number of birds infected on a global basis (WHO, 2008). However, this is not the key cause for concern. It is not what the disease has done in the past that is of concern, it is what it has the potential to do in the future that causes the greatest concern. In no instance has the virus spread beyond first generation close contacts or caused general illness in the community (WHO, 2008). However, this does not minimize the risk associated with H5N1.