Introduction Influenza, commonly known as the “flu”, is an acute viral infection of the respiratory tract caused by influenza viruses. Although it is often confused with other influenza-like illnesses, especially the common cold, influenza is a more severe disease caused by a different type of virus. A virus is a cluster of genes wrapped in a protein membrane, which is coated with a fatty substance that contains molecules called glycoproteins. Strains of the flu are identified according to the number of membranes and type of glycoproteins present.
Although Influenza is not as severe as many viral infections it’s almost the worst for viral infections of the respiratory tract. When you get the “flu” in the lungs, the lining of the respiratory tract is damaged by becoming swollen and inflamed. But the damage is not always permanent, and tissue heals within a couple of weeks. It is a respiratory disease, even though it infects the whole body. Every year, influenza strikes millions of people worldwide.
Influenza epidemics are most serious when they involve a new strain, against which most people around the world are not immune. Such global epidemics (pandemics) can rapidly infect more than one fourth of the world’s population. For example, the Spanish flu in 1918 and 1919 killed an estimated 20 million people in the U. S. and Europe and 17 million people in India. With modern society’s dependence on air travel, an influenza pandemic could potentially inflict catastrophic damage on human lives, and disrupt the global economy.
[3] Influenzas that occur every year are called “seasonal” flus. Causative Agent Influenza is caused by any of several closely related viruses in the family Orthomyxoviridae (a group of RNA viruses). Influenza viruses are categorized as types A, B, and C. The three major types generally produce similar symptoms but are completely unrelated antigenically, so that infection with one type confers no immunity against the others. 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. [7] Seasonal influenza begins in the upper respiratory tract but in serious cases may also affect the lower respiratory tract. There is a 1- to 4-day incubation period, after which symptoms begin very quickly. Extreme fatigue can last for a few days or even a few weeks.
An infection with influenza can leave patients vulnerable to secondary infections, often bacterial. [8] Diagnosis, treatment, Prevention and control of the disease Flu seasons are unpredictable in a number of ways. Although rises of flu happen every year, the timing, severity, and length of the season varies from one year to another. The CDC recommends initiation of antiviral treatment as early as possible (within the first 2 days of symptom onset) for any patient who: Is at higher risk of influenza complications, including children.