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Influenza & Colds: Strains, Treatment & Symptoms

  • Synopsis: Last Revised/Updated: 2016-01-06 - Information on influenza or flu viruses and colds with associated chills and fever muscle pains coughing weakness and general discomfort.

Influenza, commonly known as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae (the influenza viruses).

Influenza is defined as an infectious disease caused by the influenza virus. Common symptoms include: a high fever, runny nose, sore throat, muscle pains, headache, coughing, and feeling tired. In children there may be nausea and vomiting but these are not common in adults. Complications of influenza may include viral pneumonia, secondary bacterial pneumonia, sinus infections, and worsening of previous health problems such as asthma or heart failure.

The Common Cold

There are over one billion colds and cases of the flu in the United States every year. The common cold is an illness caused by a virus infection located in the nose and leads to symptoms such as runny nose, sneezing, sore throat, cough, headache, fever, etc. which are a result of the body's response to the infection. There are currently no known ways to cure a cold, we can only fight the symptoms using medicines such as antihistamines, decongestants, and cough suppressants. The best way to avoid getting a cold is to focus on cold prevention by wash your hands frequently, avoiding touching your mouth and nose, and maintaining distance from people how are infected with the virus.


A contagious respiratory illness caused by the influenza viruses. It can cause mild to severe illness, and at times can even lead to death. Influenza should not be confused with other illnesses such as avian flu, swine flu, canine flu, or pandemic flu. The flu shot is similar to an immunization in that it injects you with a small amount of inactive influenza virus which is supposed to make your body more resistant to being exposed to that virus throughout the winter. The flu shot is one of the best ways to prevent flu contamination. Once infected with the flu virus, flu symptoms can also be treated using medicines such as antihistamines, decongestants, and cough suppressants.

Influenza is a viral infection that affects mainly the nose, throat, bronchi and, occasionally, lungs. Infection usually lasts for about a week, and is characterized by sudden onset of high fever, aching muscles, headache and severe malaise, non-productive cough, sore throat and rhinitis.

The viruses pass through the air and enter your body through your nose or mouth. Between 5% and 20% of people in the U.S. get the flu each year. The flu can be serious or even deadly for elderly people, newborn babies and people with certain chronic illnesses.

Influenza is transmitted from infected humans through the air by coughs or sneezes, creating aerosols containing the virus, and from infected birds through their droppings. Influenza can also be transmitted by saliva, nasal secretions, feces and blood. Infections also occur through contact with these body fluids or with contaminated surfaces. Flu viruses can remain infectious for about one week at human body temperature, over 30 days at 0 C (32 F), and for much longer periods at very low temperatures.

Influenza infection often causes a more severe illness with a mortality rate (death rate) of about 0.1% of people who are infected with the virus. Unusually severe worldwide outbreaks (pandemics) have occurred several times in the last 100 years since influenza virus was identified in 1933.

Influenza viruses are divided into three types, designated A, B, and C.

Influenza types A and B are responsible for epidemics of respiratory illness that occur almost every winter and are often associated with increased rates of hospitalization and death.

Influenza type C differs from types A and B in some important ways. Type C infection usually causes either a very mild respiratory illness or no symptoms at all; it does not cause epidemics and does not have the severe public health impact of influenza types A and B.

Efforts to control the impact of influenza are aimed at types A and B.

In humans, common symptoms of the disease are chills and fever, pharyngitis, muscle pains, severe headache, coughing, weakness and general discomfort.[

Symptoms of influenza can start quite suddenly one to two days after infection.

Usually the first symptoms are chills or a chilly sensation, but fever is also common early in the infection, with body temperatures as high as 39 C (approximately 103 F). Many people are so ill that they are confined to bed for several days, with aches and pains throughout their bodies, which are worse in their backs and legs.

Symptoms of influenza may include:

Abdominal pain (in children with influenza B)

Body aches, especially joints and throat Coughing and sneezing Headache Irritated watering eyes Nasal congestion Extreme coldness and fever Fatigue Reddened eyes, skin, mouth, throat and nose

Vaccination against influenza with an influenza vaccine is often recommended for high-risk groups, such as children and the elderly. CDC recommends a yearly flu vaccine as the first and most important step in protecting against this serious disease.

Vaccinations against influenza are usually given to people in developed countries with a minor risk of contracting the disease.

The most common human vaccine is the trivalent influenza vaccine that contains purified and inactivated material from three viral strains. Typically, this vaccine includes material from two influenza A virus subtypes and one influenza B virus strain. A vaccine formulated for one year may be ineffective in the following year, since the influenza virus changes rapidly over time, and different strains become dominant. Antiviral drugs can be used to treat influenza, with neuraminidase inhibitors being particularly effective.

ReWalker Val, John & Claire, London, UK
fig 1. Gastrointestinal flare-up can be caused by flu virus infection in the lungs, as shown in this illustration. Illustration Credit: The Rockefeller University Press, adapted from an illustration by the authors.

Study suggests how flu-related gastrointestinal flare-ups can be relieved while the body continues to battle the virus in the lung (Rockefeller University Press)

Flu infection has long-ranging effects beyond the lung that can wreak havoc in the gut and cause a dreaded symptom, diarrhea, according to a study published in The Journal of Experimental Medicine . (fig 1.)

Gastrointestinal symptoms are often seen with flu infection, but because the virus only grows in lung cells, it's unclear how intestinal symptoms develop. Researchers in China now show that flu infection in mice prompts responding immune cells in the lung to alter their homing receptors, causing them to migrate to the gut. Once there, they produce the antiviral mediator IFN-γ, which alters the natural composition of gut bacteria. In turn, the bacterial changes lead to inflammation that promotes tissue injury and diarrhea. Blocking inflammatory molecules in the intestine or treating mice with antibiotics to deplete bacteria attenuated flu-induced intestinal injury without affecting immune responses in the lung.

Why some flu infected patients develop gastrointestinal symptoms while others do not remains unknown. However, these findings suggest ways to directly relieve intestinal symptoms like diarrhea during flu infection without interfering with the body's ability to fight the virus in the lung.

Influenza Vaccination Awareness

U.S. National Immunization Awareness Month (NIAM) - Each year in August.

National Influenza Vaccination Week (NIVW) - A national observance that was established to highlight the importance of continuing influenza vaccination. NIVW 2015 will be observed December 6-12, 2015 - (CDC)

Quick Facts: Signs & Symptoms of the Flu

People who have the flu often feel some or all of these symptoms:

WHO recommends annual vaccination for:

Latest Influenza Colds and Flu Publications

1 : Resurgence of Whooping Cough (Pertussis) in America : University of Georgia.

2 : FDA Statement Regarding Efforts to Improve Effectiveness of Influenza Vaccines : U.S. Food and Drug Administration.

3 : New SARS-like Virus WIV1-CoV May Cause Outbreak in Humans : University of North Carolina at Chapel Hill.

4 : Influenza: Symptoms of Severe Sepsis and Septic Shock : Mayo Clinic.

5 : Seasonal Flu: H3N2 Influenza : Public Health Agency of Canada.

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