The avian flu is a specific bird condition that affects all kind of birds but wild ones seem to be more resistant and carry the virus without showing any obvious signs. Poultry is most sensitive to the virus and develop the disease; mild cases evolve with respiratory symptoms, low egg production ruffled feathers. The second type of illness is the rare but lethal infection and was first discovered 1878 in Italy. The severe symptoms appear sudden and the mortality can reach 100% in less than 48 hours; the viral strain affects the respiratory tract but also produces damages to other tissues and organs and causes massive hemorrhages.

There are 16 haemaglutinins known and 9 neuraminidases and all can be found in wild birds. This makes the permanent reserve of avian flu as many of the infection viruses cause no harm in normal conditions. Most severe cases of bird flu have been caused by the subtypes H5 and H7 containing a set of basic amino acids.

All low pathogenic virus types have the possibility to become most dangerous after mutations. If earlier it was thought that waterfowls carry the low pathogenic virus, today we know they are able to transmit the most dangerous H5N1 to the visited countries. Highly pathogenic viruses can be transmitted from farm to farm by live birds, contaminated clothing, equipment, feed or cages. Very contagious virus types survive long periods of time in the environment if the temperature is low. H5N1 remains in feces for 35 days at 4 degrees Celsius. At 35 degrees the virus can survive 6 hours in faecal samples.

In cases of high pathogenic strains immediate measures such as quarantine, disinfection, proper disposal of carcasses and rapid culling of the infected birds. Strict biosecurity and sanitary measures oblige large poultry farms to isolate birds and stop the movements of live poultry. The control is easier to be done in big commercial poultry farms than in small private flocks in rural and per urban areas.

If the culling method proves unsuccessful a vaccination campaign can be recommended in high risk areas. The vaccines however must be certified by the National health organization and should be of high quality. Poor quality vaccines lead to dangerous viral mutations and can expose humans to an apparently healthy poultry population.

Backyard flocks expose humans to the infection as birds usually roam free and share water places with wild birds. These situations place humans at risk especially when birds are brought inside the household and in direct contact with children. Most common, house owners tend to sacrifice birds with illness signs and consume the meat with their families instead of alerting the authorities. Many persons especially in the country side hide their poultry during culling operations.