Each virion is covered with a lipoprotein envelope that is studded with glycoprotein spikes acquired during viral maturation. The A viruses cause the great influenza epidemics, and the B viruses cause smaller localized outbreaks; the C viruses are not important causes of disease in humans. Influenza A viruses are classified into subtypes, and both influenza B and subtypes of influenza A are further divided into strains. Subtypes of influenza A are differentiated mainly on the basis of two surface antigens (foreign proteins) "hemagglutinin (H) and neuraminidase (N). Examples of influenza A subtypes include H1N1, H5N1, and H3N2. Strains of influenza B and strains of influenza A subtypes are further distinguished by variations in genetic sequence. [1] .
Signs and Symptoms.
Influenza is an acute respiratory illness characterized by fever, headache, dry cough, sore throat extreme tiredness, runny or stuffy nose, muscle aches, stomach symptoms, such as nausea and vomiting and diarrhea. Some of the complications caused by flu include bacterial pneumonia, dehydration, and worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes. [2] The flu virus is usually spread in the small droplets of saliva coughed or sneezed into the atmosphere by an infected person. Direct contact with hands contaminated with the virus can also spread infection. .
Influenza is a highly infectious viral disease. Most people who get influenza will recover in a few days to less than two weeks, but some people will develop complications (such as pneumonia) as a result of the flu, some of which can be life-threatening and result in death.
Pneumonia, bronchitis, sinus and ear infections are examples of complications from flu. The flu can make chronic health problems worse. For example, people with asthma may experience asthma attacks while they have the flu, and people with chronic congestive heart failure may experience worsening of this condition that is triggered by the flu.
