History
In 1997, a line of H5N1 avian influenza was transmitted to a child in Hong Kong who died with respiratory problems. This was the first of successive recorded cases of transmission of this virus from birds to humans breeding.
Since then, the world worried accompanies the movement of this virus. Though related to severe cases in humans, this type of influenza can also cause severe symptoms in birds. So, he is classified into two types, or HPAI highly pathogenic, causing thousands of deaths in wild and domestic birds, and serious health problems in humans and the little pathogenic or LPAI, which infects birds and is asymptomatic. The highly pathogenic H5N1 cause various health complications in humans, with nerve damage and liver, besides the respiratory treatment. Nonetheless, it is not efficiently transmitted between humans, being made by those who have direct contact with poultry or close.
Currently, we know that H5N1 is now circulating in birds established and created in Asia. The virus was detected in several countries in Asia, Europe and Africa, being carried by migratory birds and often pollute local poultry.
The highly pathogenic H5N1 has a number of uncommon features that concern us. The most obvious is the fatality, no other Influenza can kill such a large portion of those infected. More than half of those confirmed as contracted, died. And a number of complications ranging from the more common and more severe respiratory problems and rare and neurological complications. Of 442 cases reported to WHO until today, 262 were fatal. It is worth remembering that the lethality must be less than recorded once and 
everyone is looking for hospitals, mainly in asymptomatic cases.
It is not just human cases that concern us. Breeding animals are also severely affected. Estates where many losses had occurred anchored by infection excluding cases of animals are slaughtered to prevent the spread of the virus, usually all the local and neighborhood. In the wild environment, wild animals often are found dead and tested positive for the virus. Like eagles and geese.
Another concern is the breadth of hosts that H5N1 can infect. Besides a large variety of birds – geese, swans, turkeys and even flamingos, among others – several animals that are not normally associated with influenza and were found with the virus, including big cats such as tigers and leopards that fed on chickens in a zoo in Thailand. A cat was infected after eating a pigeon in 2004, also in Thailand.
To date, only one case of human to human transmission was confirmed in 2005, and some remain suspicious but unconfirmed. A sick child transmitted the virus to her mother, probably have a very close contact in between. This lack of transmission events between individuals indicates a low efficiency of the virus to spread between humans.
Although it is not transmitted between humans, scientists, health workers and governments monitor suspicious movement of H5N1. In the next text, we will see what characteristics of the virus may contribute to that he is not properly transmitted and what can explain its pathogenesis, and what does it cause for concern.
Why is it so dangerous H5N1?
Of the 112 subjects who were infected by the H5N1 strain of bird flu, more than half (57) died, representing a mortality rate of 55%, a percentage exceeding in the three major epidemics of flu that humanity has experienced, including the Spanish flu of 1918.
These deaths have been located in rural areas of four Asian countries: Vietnam, Thailand, Cambodia and Indonesia. However, both the FAO (United Nations Organization for Food and Agriculture) and the World Health Organization (WHO) explain that cases of human infection are rare and that the virus does not spread easily from birds poultry to humans. But H5N1 has some special characteristics.
Although scientists still do not quite understand why this virus is so lethal, some experts suggest what may be the primary keys of the dangerous H5N1.
Flu viruses tend to invade the cells of the throat and trachea, where they multiply and cause an inflammation that is opposed by the immune system. In some cases, the organism can reach the lungs and cause pneumonia.
However, unlike their ‘similar’, the avian influenza virus has the ability to multiply in many other parts of the body as well as in the throat and trachea, and the liver, intestines or brain. So what would ordinarily be a respiratory disease may become widespread infection throughout the body.
Furthermore, the close coexistence of millions of people, chickens and pigs, as in China, has encouraged the rapid spread of avian influenza from Southeast Asia and has allowed two different influenza viruses are in the same organism, a Indeed, rare, resulting in a new strain of virus.
Finally, the more times a virus multiplies more possibilities of the emergence of a mutation can be passed from person to person. Thus, many scientists say the elimination of outbreaks of H5N1 in birds, which can be replicated many times a day is an essential step in preventing the spread between humans.
The WHO warning
The World Health Organization has warned several times about the importance of being prepared for a likely outbreak of bird flu. The program manager for the flu, Klaus Stohr, said that “despite warnings in recent years that a new pandemic is inevitable and the need for countries to have prepared contingency plans, only 50 out of 200 countries they have been drafted.
Along the same lines express members of the international scientific community because they believe there is a high risk of occurrence of another flu epidemic similar to the years 1918, 1957 and 1968, which ended the lives of over 100 million people in the world.
So far, the H5N1 avian flu virus is the only one of the 15 types of virus can be lethal to humans.