The flu, or influenza, is a crafty virus that can really give you chills. This sneaky germ does not care how old you are; it’s more than happy to mess with anyone. When it strikes, it’s like a wildfire that swiftly spreads from one person to another. It takes a particular interest in messing with your respiratory system. Because of its ability to change shape and structure, its treatment poses a formidable challenge to medical advancements—a significant reason for the influenza virus to be responsible for causing epidemics and pandemics in recent decades. Every year, millions of people get influenza infection.

What is Influenza?

Influenza, or the flu, is a communicable respiratory disease of the upper respiratory tract. When the influenza virus visits you, you can expect some pretty typical symptoms like headaches, body aches, that pesky dry cough and a sore throat. Every winter, typically from December to February, the influenza virus has its way with a whole bunch of folks, and now and then, it even takes things up a notch and becomes an epidemic.

Figure 1. A child infected with the influenza virus.

Causes of Influenza – flu

The flu or influenza is mainly caused by the influenza virus. This virus has four main variants, and it can cause flu in humans as well as animals. These four categories are labeled as types A, B, C, and D of the influenza virus.

Type A influenza is primarily associated with infections in aquatic birds, humans, and pigs. This type A has further subtypes, which are classified on the basis of structural differences in their viral proteins. The most common subtype is called H1N1. This subtype is mainly associated with bird flu and swine flu.

The type B influenza virus is the most common pathogenic cause of flu or influenza in humans; however, it may also affect animals, such as dogs and pigs.

Type C influenza typically causes a mild infection in humans, primarily in kids, usually without the appearance of flu symptoms.

Finally, the type D influenza virus mainly infects cattle and pigs. Oppositely, to date, the influenza D virus has not been found infecting humans.

Transmission of Influenza Virus or Flu

Humans can get influenza virus infection through multiple transmission channels. These methods are:

  • direct contact via person-to-person transmission,
  • direct contact via object-to-person transmission,
  • aerosol inhalation of viral particles.

Person-to-person transmission

Direct contact of transmission mainly involves the transmission of viral particles through nasal secretions. The flu can make your nose run, and that stuff might have the virus in it. If an infected person touches their nose or eyes, that virus can get on their hands. As a result, the influenza virus can easily spread to other non-infected persons through handshaking. These individuals may later touch their noses or eyes with their virus-exposed hands.

Object to personal transmission

In the same way, contaminated objects, also called fomites, are also responsible for the direct transmission of the influenza virus through non-living objects such as tabletops, floors, doorknobs, or clothes to humans. Suppose an infected person touches their nose and eyes; the virus can get on their hands. Consequently, when a person touches tabletops, floors, doorknobs, or clothes, they easily transmit viral particles to these surfaces, which can be the potential source of influenza transmission to non-infected persons when they obliviously touch these contaminated surfaces.

Through extensive genome-level research, scientists have indeed confirmed the presence of Influenza viral RNA on roughly 23 to 59% of everyday household and daycare items. Studies have also revealed the potential persistence of infectious influenza virus on paper currency for several weeks.

Aerosol transmission:

Moreover, aerosol or respiratory transmission of influenza virus mainly occurs through the release of aerosols or droplets of nasal secretions containing virus particles. For instance, singing, speaking, coughing, sneezing, and even breathing may also generate droplets. Coughing may result in the release of several hundred droplets, while a good sneeze can release up to 20,000 droplets.

Depending on the expulsion force and size, large air droplets fall on the ground within a few meters vicinity. In contrast, small air droplets of one to four microns in size remain suspended in the air for even longer periods. Therefore, virus-contaminated air droplets may be immediately transmitted to healthy individuals in the vicinity. When a virus enters the human body through breathing, it is held in the upper respiratory tract, where it may start infection.

There is a well-known outbreak of influenza virus through aerosol transmission, in which an airplane carrying 54 individuals was delayed to the ground for three hours. Although a single person was the source of influenza infection in the aircraft, the ventilation system of this airplane was non-functional, which resulted in almost 75% of its passengers developing influenza due to aerosol transmission.

The influenza virus targets the human upper respiratory tract and results in inflammation, leading to an acute disease. Although the influenza virus disease is self-limiting in most individuals, its symptoms usually persist for 7 to 10 days. Inflammation usually occurs due to an immune response to the infection and the response of interferons, resulting in the appearance of symptoms, including fever, body aches, and coryza. Individuals, such as those already infected with cardiac disease, pregnancy, and chronic lung disease, are more vulnerable to severe complications such as primary viral pneumonia, secondary bacterial pneumonia, hemorrhagic bronchitis, and, ultimately, the death of an individual.

Signs and Symptoms of Influenza Virus or Flu

Seasonal influenza usually results in fever, headache, dry cough, muscular pain, sore throat, runny nose, and severe malaise. The seasonal flu cough can be severe and can last for two or more weeks. In most cases, influenza symptoms disappear on their own within a week; however, sometimes, severe illness and death may occur, especially in high-risk groups.

Diagnosis of Influenza Virus or Flu

Numerous diagnostic tests are available to identify influenza virus in respiratory samples from suspected individuals. However, commonly used methods with varied sensitivity and specificity are

  • “rapid influenza diagnostic tests.”
  • “rapid molecular assays”
  • immunofluorescence assays,
  • viral culture
  • reverse transcription polymerase chain reaction, in short RT-PCR.

Rapid diagnostic tests detect viral antigens and produce results within 10 to 15 minutes.

Rapid molecular assays are genome-level tests that detect the genetic material of the influenza virus. These tests produce results within 15 to 20 minutes. Although both these tests are rapid, they are less accurate than other available tests.

Contrarily, viral culture is a sophisticated, accurate, and reliable test; however, it is time-consuming and may take days to detect the virus.

The RT-PCR test takes hours to detect the virus, but it is the currently available influenza virus test with the highest accuracy.

Treatment of Influenza Virus or Flu

The flu is usually mild and recovers on its own without any medical intervention. However, supportive therapy may be recommended to relieve symptoms. The supportive treatment involves:

  • taking rest,
  • maximum fluid intake,
  • particular water,
  • paracetamol administration to relieve pain and fever,
  • taking decongestant medicines to relieve cough

Sometimes, mild flu may progress to severe respiratory conditions, which require immediate hospital admission and emergency treatment to prevent death.

  • After a confirmed diagnosis, antiviral drugs are prescribed for respiratory illness caused by influenza virus infection.
  • Influenza virus subtypes A and B are commonly treated with neuraminidase inhibitors family.
  • The chances of resistance to these antiviral drugs have been minimal in recent influenza seasons; however, the virus may mutate and develop resistance at any time.
  • Sometimes, respiratory illnesses may not be necessarily caused by the influenza virus; rather, they may be caused by a common cold or bacterial pneumonia. In these cases, antibiotics, not antiviral drugs, are prescribed to reduce and eliminate bacterial infections.

Prevention of Influenza Virus or Flu

Vaccination is the best available preventive measure to protect themselves from the influenza virus; however, because the virus mutates and replicates, a new vaccination is required every year to ensure protection.

Figure 2. Preventive measures to avoid influenza infection.

The vaccine will be available in injections and nasal spray form. The nasal spray vaccine is recommended for people between the ages of two and 49 and not recommended for pregnant women, children aged 2 to 4 experiencing asthma, people with weak immune systems, and people who have high allergic reactions to a flu vaccine.

Some other preventive measures include:

Avoid crowding, clean the surfaces of your home, cover your cough, then sneeze, and avoid touching the face during influenza.

Final Thoughts

An October 2023 report by the World Health Organization reveals that about a billion people are affected by influenza globally, from which almost 3 to 5 million people are experiencing severe illness. Influenza was first discovered by Richard Pfeiffer in 1892. This disease happens due to a virus that causes a mutation in the immune system of the body. A person with influenza may experience fever, cough, sore throat, and body itching. Vaccination is the best way to prevent this disease.

Frequently Asked Questions – FAQs

How Influenza A virus is serious?

Influenza A infection is more common than the common cold, which usually affects people in winter and causes severe disease.

How flu or influenza is treated?       

Antiviral drugs are recommended to treat influenza, but they are different from antibiotics. Antivirals are prescription medicines in the form of pills, liquids, or intravenous solutions.

How is influenza diagnosed?

The most common is the rapid influenza diagnostic test. This test detects the part of the virus that stimulates immune response and provides results within 10 to 15 minutes.

About the author

Dr. Madilyn Adams has a Ph.D. in molecular medicine from Harvard University and has been working as a medical blogger for seven years.


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