Introduction

The word influenza comes from the Italian language refers to cause of the disease.In Italian influenza means “influence’’,(Latin Influentia).Influenza,commonly referred to as the flue ,which is an infectious disease caused by RNA viruses of the family Orthomyxovividae (the influenza viruses) which affects birds and mammals.Influenza spreads around the world in sesonal epidermics, resulting in the deaths of hundreds and thousand annually. Three influenza pandemics resultingoccured in the 20th centuary by the appeareance of a new strains of the virus in humans.Often,these new strains appear when an existing flu virus spreads to humans from other animal species ,or when existing human strain picks up new genes from a virus that usually infects birds or pigs .
The most common symptoms of this disease are chills,fever,sore throat,muscle pains ,severe headache,coughing ,weakness and general discomford.Usually ,vaccinations against influenza is givento people in developed countries and tofarmed poultry .The most common human vaccine is trivalent influenza vaccine(TIV) that contains purified and inactivated material from three viralstrains.A vaccine formulated for one year may be ineffective in the following year,since the influenza virus evolves rapidly and new strains quickly replace the olders ones.