Subtypes
The virus' surrounding sheath contains two proteinsubstances also called surface antigens. One is called haemaglutinin (H) and it binds the virus to the host cells. The other is an enzyme called neuraminidase (N) and it releases the virus from infected cells. These surface antigens are divided into subtypes, indicated by a number, for example H5N1.
Modes of transmission
The virus is normally only present in the gastro-intestinal tract of birds and is excreted with the faeces, but the very serious and infectious variant can also be located elsewhere in the bird. Studies show that in ducks the bird flu spreads and mutates particularly fast - for this reason, they constitute a particularly high risk factor.
It has been proven that cats can be infected with H5N1. They are most likely infected by eating infected birds. H5N1 is not transmitted from cats to people. Researchers fear that the virus could mutate so that a variant is created that can be transmitted from cats to people.
Vira from bird droppings contaminate soil and dust particles and is spread with the wind. In cases where birds infect humans, it happens when the bird flu virus is inhaled or when the person rubs his/her eyes with a hand contaminated with virus.
In other words, direct contact with infected animals or exposure to relatively large quantities of the virus are required to become infected with the disease. Temperature, however, is a major factor in the spreading of bird flu in nature. Tests have shown that the virus can survive more than a month at refrigerator temperature, but does not thrive in the higher summer temperatures.
What is feared about bird flu is that from posing a very small health risk to humans, it suddenly mutates so that it no longer only infects from birds to humans but from one person to the next. This may happen if a person infected with regular flu is exposed to bird flu virus. In this manner it will be possible for the two types of vira to exchange genes, so that a completely new type is formed which the immunesystem is not familiar with and therefore cannot defend against. A British inquiry is said to have established such a case in which a Thai mother died of bird flu after being infected by her daughter. There have been other examples of bird flue of the type H5N1 passed on between family members, in other words those who are closely genetically connected. If the assumption that the bird flue can only be spread between family members is true, it will reduce the risk of a pandemic.
The Spanish flu
The so called Spanish Flu, which raged from 1918-1920, has been shown to be a flu virus of the type H1N1. The disease did not begin in Spain. It was first detected in a military base in Kansas, USA. The Spanish Flu received its name because the Spanish newspapers wrote most prolifically about the disease. In Spain the disease was called the French Flu. It is believed that 525 million people were exposed worldwide. Of these 50 million people perished. In the UK about 250,000 people died.
The unique characteristic of the Spanish Flu, and one thing which has astonished researchers was that many of the infected were both young and healthy, so that their immune systems may be believed to have been strong. Typically death occurred only five days after the first symptoms.
After extensive detective work, researchers were able to track down lung tissue samples from 1918 as well as two flu victims buried in Alaskan permafrost. This gave sufficient material so that the researchers, in 2005, could reconstruct the fatal virus of 1918. Based on this, researchers now believe that the virus’s high death rate is due to that it causes the immune systems of the exposed to overreact. An overreacting immune system is also known from several forms of allergies.
Symptoms after infection
In principal, all birds can be infected. Infection with the mild form will cause the bird to have a ruffled coat of feathers and lay fewer eggs. In the more serious form, the bird might die within 24 hours of being infected.
Bird flu attacks the airways deeper than regular fly. People infected with bird flu will get pneumonia accompanied by high fever. A sore throat can appear as well as coughing and respiratory problems. In the most serious cases, severe pneumonia and serious breathing difficulties will occur. Symptoms such as vomiting, diarrhoea, abdominal pains and bleeding are not uncommon either.
The bird flu virus cannot tolerate high temperatures and dies when heated to 60 degrees Celsius (140 degrees Fahrenheit) for 30 minutes. Thoroughly done poultry should be safe to eat. Boiled eggs are also believed to be safe food.
