Student Presentation on

INFLUENZA

by Chirag Kamdar

Introduction

One can claim that influenza is an infection that has victimized people from just about every generation that we have known. The term Influenza comes from the Latin word "influentia", first used by the Italians in the 1600's. It is a highly contagious infection particulary of the respiratory tract.In addition to us humans, influenza can occur in pigs, horses, and several other mammals as well as in certain wild and birds. It can also jump from specie to specie as observed in late 1997 when influenza from chickens was having its effects on people in Hong Kong. Because influenza is highly contagious and spreads easily, it has appeared in our history many a times as epidemics. Influenza is caused by an Orthomyxovirus which is spherical in shape and has single stranded RNA. It is an envelpoed virus, therefore it gets greater protection from its environments. There are three types of influenza known to us right now:

Type A - common in 5-19 year olds, epidemics occur most winters
Type B - generally smaller epidemic outbreaks
Type C - rare, but can cause serious health problems

 

Encounter & Entry

Flu season in temperate regions typically begins with the approach of winter—November in the Northern Hemisphere, April in the Southern Hemisphere. 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. Influenza is caused by viruses being transmitted from one to another person in the form of droplets coughed or sneezed into the air. The virus consists of an inner core of the genetic material RNA surrounded by a protein coat and an outer lipid envelope which project spikes of proteins called hemagglutinin and neuraminidase. Hemagglutinin is very important for the virus to bind to animal cells, for example, a human red blood cell. This causes agglutination which is the clumping of the red blood cells. Tests based on this simple clumping of the red blood cells is useful to determine if one has influenza. The neuraminidase is used to cut off the viruses hemagglutinin receptors when new viruses are produced and start budding off. It also degrades the mucosal surfaces of the lungs and the throat to prevent being ejected. This hampers the ability of the antibodies of getting into the lungs.




Spreading & Multiplication


As soon as the virus is in the body, it uses the hemagglutinin to bind to the cell surface. The membranes of the virus and the cell fuse togather and the capsid that contains the single stranded RNA is released into the cytoplasm. The protein coat of the virus dissassembles and then starts making viral proteins and viral RNA copies. The new virus proteins are put togather near the cell membrane and then bud off from the membrance. Influenza has a rapid onset and pronounced symptoms. After the influenza virus invades a person’s body, an incubation period of one to two days passes before symptoms appear. For most people flu symptoms begin to subside after two to three days and disappear in seven to ten days. However, symptoms like coughing and fatigue may persist for two or more weeks.

Follow these links to learn more about the life cycle of influenza:

http://webs.wichita.edu/mschneegurt/biol103/lecture14/lecture14.html

Response to Host Defenses

Viruses are very versatile. Whenever there is a possiblility of getting "rejected" by the host cell, or being "caught" by antibodies, the virus changes the hemagglutinin receptors and flourishes on until the body can come up with an antibody. If the virus is not able to perform this function, it will be rendered useless against an on-slaught of antibody clones. Diversity in the viral receptors makes it hard for the body to keep up with the changes. This essentially cause it to be a new antigen and thus escape previous immunity to influenza virus. Slight modifications in the genome of the virus can lead to changes in the surface antigens of the virus. Sometimes only a single nucleotide can cause the change - often called a "point mutation". These little changes can lead to epidemics because some percentage of the population have never had to face such a virus with altered receptors. The minor changes in the antigenicity of the virus is called an antigenic drift. Such drifts can be seen in both types of influenza, A and B. Major changes like exchanging of the viral genomic RNA can also occur, called reassortment. For example, this can occur when our cells are infected with 2 different strains of the virus. This mixing of the genetic information can cause major epidemics or even pandemics. These large modifications are called antigenic shifts and are observed in type A influenza only.

 

Transmission & Damage

Scientific evidence suggests that influenza viruses in mammals are derived from viruses in wild ducks and waterfowl. Some of these viruses could have been acquired by humans thousands of years ago. An individual can start spreading the flu even before they get sick and start experienceing the symptoms. Adults can continue to pass the flu virus to others for another three to seven days after symptoms start.  Children can pass the virus for longer than seven days.  Symptoms start one to four days after the virus enters the body. Some people become only carriers, spreading the disease, but feeling no effects themselves.

 

Outcome

Influenza is characterized by fever, headaches, muscle aches, and fatigue and shivering. Most people recover completely in about a week but some people are vulnerable to complications such as bronchitis and pneumonia. This group of people includes children with asthma, people with heart or lung disease, and the elderly. In the United States, people age 65 and older account for about 90 percent of influenza-associated deaths. In most years less than 1 percent of those infected die. The United States Center for Disease Control and Prevention (CDC) estimates that influenza causes more than 20,000 deaths in the United States each year; combined, influenza and pneumonia are among the nation’s ten leading causes of death. The influenza pandemic that occurred between 1918 and 1919, the worst ever, killed about 500,000 people in the U.S. and more than 20 million people worldwide. Death from influenza is very rare, but can occur in many people. Influenza can enhance the underlying medical conditions, such as heart or lung disease. Influenza viruses produce inflammation in the lining of the respiratory tract, increasing the risk that secondary infections will develop. Common complications include bronchitis and bacterial pneumonia, occurring mostly in the elderly, people on chemotherapy, and people with AIDS or another disease that have a compromised immune system.

 

Is there a cure?

No cure for influenza has yet been discoered or invented. Only treatments like bed rest and increased intake of fluids can lessen in severity. Few drugs have been found to lessen the flu symptoms. Prevention via vaccines seems to be the only way out.Pharmaceutical drugs cannot cure influenza, but certain antiviral drugs can relieve flu symptoms. Available by prescription only, these drugs provide some relief, but only if taken on the first or second day of symptoms. The drugs amantadine (sold under the brand name Symmetrel) and rimantadine (Flumadine), both in pill form, work against hemagglutinin receptors and effectively treat type A influenza. Oseltamivir (Tamiflu) in pill form and zanamivir (Relenza), an inhalant disrupts the action of the neuraminidase and works for both type A and type B influenza. A flu vaccine consists of greatly weakened or killed flu viruses, or fragments of the dead viruses. These fragments in the vaccine stimulate an individuals immune system to produce antibodies against the viruses. If the flu viruses invade a vaccinated person at a later time, the already sensitized immune system recognizes the antigens and quickly responds to destroy the viruses. About 5 to 10 percent of people, especially children, who receive a flu vaccine experience mild, temporary side effects, typically soreness at the injection site.

 

Prevention Is The Best Medicine

The CDC ecommends that people who are at high risk of developing secondary complications should take flu vaccines. This group includes people of age 65 and older; people in nursing homes and other facilities that house people with chronic medical conditions (nosocomial disease); people with chronic heart, lung or kidney disease, diabetes, an impaired immune system, or severe forms of anemia. It takes the human immune system one to two weeks after vaccination to develop antibodies to the flu antigens. According to the CDC, the best time to get flu shots is between October 1st and mid-November, which is well in advance of the peak of influenza season. The success of flu vaccines varies from one person to another. In healthy young adults, the vaccines are 70 to 90 percent effective in preventing the disease. In the elderly and people with certain chronic medical conditions, the vaccines are less effective in preventing illness but help reduce the severity of an infection and the risk of major complications or death. Studies show that flu vaccines reduce hospitalization by about 70 percent and death by about 85 percent among the elderly. Of course, basic common sense things like washing hands several times a day can immensely reduce the risk of coming down with influenza.

At this sitehttp://www.cdc.gov/flu/weekly/fluactivity.htmyou can find up to date information for the US.

References

http://www.cdc.gov/ncidod/diseases/flu/fluinfo.htm

http://webs.wichita.edu/mschneegurt/biol103/lecture14/lecture14.html

 

© 2010, J.Graf. Site made by Chirag Kamdar, for comments please contact Joerg.Graf@uconn.edu