Influenza

Influenza, also known as flu, is a contagious infection of the respiratory tract. Influenza is sometimes referred to as grippe. Influenza is caused by a virus transmitted from one person to another in droplets coughed or sneezed into the air.

Most people recover completely in about a week. But some people are vulnerable to complications such as bronchitis and pneumonia.

Because influenza is highly contagious and spreads easily, it usually appears as epidemics—that is, outbreaks involving many people. If an outbreak spreads around the world—not uncommon in this age of rapid international travel—it is called a pandemic.

 

Today scientists know that the virus consists of an inner core of the genetic material ribonucleic acid (RNA) surrounded by a protein coat and an outer lipid (fatty) envelope from which project spikes of proteins.

 These proteins act as antigens—that is, they cause an immune response in the human host that the virus invades. In addition to their role as antigens, the proteins enable the virus to bind to and invade cells and virus to move among cells.

Influenza viruses pass from person to person mainly in droplets expelled during sneezes and coughs. When a person breathes in virus-laden droplets, a protein on the surface of the virus binds to enzymes in the mucous membranes that line the respiratory tract.  The enzymes, known as proteases, enable the virus to gain entry into cells and begin to multiply.

Although an influenza epidemic can occur at any time of year, flu season in temperate regions typically begins with the approach of winter. Flu viruses spread more easily during cold weather because people tend to spend more time crowded together in homes and schools, as well as buses, subways, and other places with poor ventilation. An epidemic may be restricted to a town or city or may quickly spread geographically as infected people travel aboard motor vehicles, airplanes, and ships.

After the influenza virus invades a person’s body, an incubation period of one to two days passes before symptoms appear. Classic symptoms include sore throat, dry cough, stuffed or runny nose, chills, fever with temperatures as high as 39º C (103º F), aching muscles and joints, headache, loss of appetite, occasional nausea and vomiting, and fatigue. For most people flu symptoms begin to subside after two to three days and disappear in seven to ten days. However, coughing and fatigue may persist for two or more weeks.

Death from influenza itself is rare. But influenza can aggravate underlying medical conditions, such as heart or lung disease.

Common complications include people with acquired immunodeficiency syndrome (AIDS). 

There is no specific cure for influenza. Recommended treatment usually consists of bed rest and increased intake of nonalcoholic fluids until fever and other symptoms lessen in severity. 

 

Read the article on the left and answer the following questions:

  1. What type of pathogen causes influenza (flu)?


  2. How is influenza transmitted from one person to another? (three ways please)



  3. Describe two specific effects of influenza on the body.

  4. Can influenza be treated by antibiotics? Explain your answer.








  5. How does the skin help to defend us against Influenza?




  6. What type of chemical are the antigens on influenza?

  7. What would a Lymphocyte do if it attached to an antibody on an influenza particle?




  8. What difference would there be in the response by phagocytic leucocytes and lymphocytes, in order to get rid of the influenza and how?





  9. Explain why influenza is more dangerous to people with AIDS than to those without HIV.

 

Drugs That Ease Symptoms

No drugs can cure influenza, antibiotics have no effect but certain antiviral medicines can relieve flu symptoms.

Vaccines

A flu vaccine consists of greatly weakened or killed flu viruses, or fragments of dead viruses. Antigens in the vaccine stimulate a person’s immune system to produce antibodies against the viruses. If the flu viruses invade a vaccinated person at a later time, the sensitized immune system recognizes the antigens and quickly responds to help destroy the viruses.

Flu viruses constantly change so different virus strains must be incorporated in vaccines from one year to the next. Scientists try to provide a good match between the vaccine and the most serious virus strains circulating at the time.

It takes the human immune system one to two weeks after vaccination to develop antibodies to the flu antigens. 

Flu shots must be given annually for two reasons. First, antibody protection provided by the vaccine decreases during the year following vaccination. Second, vaccines created for pre-existing viral strains may not work against new strains; nor does an infection with one flu strain confer immunity to infection by another strain.

You can blame the ducks

Evidence suggests that all influenza viruses in mammals, including humans, derived from viruses in wild ducks and other waterfowl. Some of these viruses could have been acquired by humans thousands of years ago. But medical historians know of no clearly identifiable influenza epidemics until large-scale outbreaks occurred in Europe in 1500s

In the 20th century, major pandemics occurred in 1918-1919, 1957-1958, and 1968-1969. The 1918-1919 pandemic was the most destructive in recorded history. It started as World War I (1914-1918) was ending and caused 20 million deaths—twice as many deaths as the war itself. When and where the pandemic began is uncertain, but because Spain experienced the first major outbreak, the disease came to be called the Spanish flu. The virus was exceptionally lethal; many of the deaths were among young adults age 20 to 40, a group usually not severely affected by influenza.