Main Info | Symptoms | Treatment | H5N1

The Special Subtype

All bird flu viruses are classified as type A influenza viruses which affect animals such as birds, pigs, horses, whales as well as humans. H5N1 is a subtype within type A influenza viruses that don’t characteristically infect humans and has never done so, until the first appearance of human H5N1 infection in 1997. The H5N1 subtype is a highly pathogenic form of avian influenza that was first isolated in 1961 in South Africa. It’s lethal among birds and has also had a considerably high mortality rate among humans as well, killing over 50% of all victims. As of November, the virus is documented to have affected poultry in 13 different countries worldwide, with a large proportion of Asia affected.

Pandemic Potential

The particular apprehension over H5N1 (compared to other species of bird flu) is due to its high capability of becoming a vastly contagious, virulent and sustainable disease that will produce a global pandemic. Many scientists have predicted that a future pandemic is set to transpire and is now simply down to a matter of time. According to the standards of the World Health Organisation, human H5N1 infection already satisfies two of the three key points to defining a pandemic.

1. The virus is foreign to humans and we have little resistance against it and;
2. The virus causes severe disease.

Should H5N1 successfully become infectious between humans, then a worse case scenario of worldwide death figures ranging from 2 million to 1 billion deaths has already been estimated.

Reasons Behind its Deadliness

H5N1 infection in the body causes an excessive onset of human hormones known as cytokines, producing a cytokine storm. Cytokines are normally beneficial against infections if they exist in the right levels and they help regulate the immune system. However, an excess of cytokines becomes provocative against the body, leading to symptoms like fever, vomiting, chills and headaches etc. typical to H5N1 infection.

Under normal circumstances, other diseases that also trigger a cytokine storm are less lethal because whilst triggering the release of inflammatory compounds that harm the body, anti-inflammatory agents are also produced, restraining the extent of damage. In spite of this however, H5N1 is capable of lowering the levels of anti-inflammatory agents released and is resistant against infection-fighting cytokines, rendering the human immune system useless and leading to lethal conditions.

Furthermore, once a cytokine storm is triggered, antiviral medications are useless against it. Thus it's necessary for antivirals to be consumed in the early stages of infection, before the onset begins, in order to effectively control the infection. However, current developments are suggesting that the answer to belated treatment may lie in a new drug, capable of controlling the cytokine storm after its onset. The new treatments in development are expected to be used in conjunction with existing antivirals and are expected to boost the effectiveness of antiviral drugs like Tamiflu and Relenza. Such drugs are design to bind to the glycoproteins of each virus particle and capture them before they infect the cells. This in turn minimizes the production of cytokine and deters the onset of a cytokine storm. So far however, tests have only been run on samples of human blood, but research in this area may result in a key weapon against H5N1.

Animals Infected

Although birds remain the chief target of avian influenza viruses, humans, pigs, leopards and tigers have also been documented as victims of H5N1 infection. Household cats were found to contract H5N1 under experimental conditions in the Netherlands and leopard and tiger cases were recorded in Thailand, where the virus currently circulates in the country’s bird population. Pigs have always been known to be susceptible to a variety of influenza types, both those typical to humans and birds. As of yet, these remain the only animals that have been affected.

Virus Mutation

Scientists in Vietnam have recently unveiled evidence that H5N1 is slowly altering to become an even greater threat to the human population - a sign that confirms fears of the virus triggering the next global pandemic. Following the breakdown of 24 different strains of H5N1 extracted from human victims as well as poultry, the Ho Chin Minh Pasteur Institute found various changes in the virus’ surface proteins, with one particular sample showing alterations that would produce an increased virus breeding efficiency in mammals. However, no inferences about the mutations’ effects on human-to-human transmissions have yet been made and H5N1 remains more or less a potential threat rather than a definite danger at this stage.

Victim Trail

As of April 12 2006, there were a total of 109 deaths and 194 laboratory confirmed cases of human avian influenza infection (due to H5N1) in 9 different countries. Of these, the first cases of human H5N1 contraction and subsequently death were reported in Vietnam and Thailand, followed by Cambodia, Indonesia, China, Turkey, Iraq, Azerbaijan and Egypt. Figures are given below:

Country	Total Cases	Deaths	Mortality Rate
Vietnam	93	42	45%
Thailand	25	17	68%
Cambodia	6	6	100%
Indonesia	74	56	76%
China	21	14	67%
Turkey	12	4	33%
Iraq	3	2	67%
Azerbaijan	8	5	63%
Egypt	15	7	47%
Djibouti	1	0	0%
Total	258	153	59%

Source: WHO: (URL)

A large number of countries have further reported the existence of H5N1 in domestic poultry populations, but have not had any cases of human infection. These include:

• Croatia
• Laos
• Kazakhastan
• Mongolia
• Russia
• Romania
• Ukraine
• Nigeria
• India
• Malaysia
• Niger
• Albania
• Myanmar
• Afghanistan
• Israel
• Jordan
• Burkina Faso

Japan and the Republic of Korea (North Korea) were also previously included among the list, but after extensive cullings were later verified bird flu free by the OIE at this point in time.