Influenza Virus

Influenza, commonly referred to as the flu, is an infectious disease caused by the influenza virus. Despite being a familiar term, the intricacies of this virus, its symptoms, types, and treatment options are often misunderstood.

There are four types of influenza viruses: A, B, C, and D. Influenza A and B viruses are the most common and are responsible for the seasonal flu epidemics observed almost every winter. Influenza C infections cause a mild respiratory illness and are not thought to cause epidemics. Influenza D viruses primarily affect cattle and are not known to infect humans.

Influenza Virus Symptoms

The symptoms of influenza can range from mild to severe and can sometimes lead to hospitalization and even death. Common symptoms include:

• Fever: High body temperature, often accompanied by chills.
• Cough: Persistent and can be severe.
• Sore Throat: Pain or irritation in the throat.
• Runny or Stuffy Nose: Nasal discharge or congestion.
• Muscle or Body Aches: Generalized pain in muscles.
• Headaches: Persistent and often severe.
• Fatigue: Extreme tiredness and lack of energy.
• Vomiting and Diarrhea: More common in children than adults.

These symptoms typically appear suddenly and can last for several days to a couple of weeks. It's crucial to note that not everyone with influenza will have a fever.

Causes of the Influenza Virus

The influenza virus spreads mainly through tiny droplets made when people with flu cough, sneeze, or talk. These droplets can land in the mouths or noses of people who are nearby. Less often, a person might also get the flu by touching a surface or object that has the flu virus on it and then touching their mouth, nose, or possibly their eyes.

Factors that contribute to the spread of influenza include:

• Close Contact: Being near infected individuals increases the risk of transmission.
• Crowded Places: Public spaces with large gatherings facilitate the spread.
• Poor Hygiene: Inadequate handwashing and respiratory hygiene contribute to transmission.

Types of Influenza Virus

Influenza A

Influenza A viruses are divided into subtypes based on two proteins on the surface of the virus: hemagglutinin (H) and neuraminidase (N). There are 18 different hemagglutinin subtypes and 11 different neuraminidase subtypes. Examples include H1N1 and H3N2. Influenza A viruses are known for their potential to cause pandemics due to their ability to infect a wide range of animal hosts and undergo significant genetic changes.

Influenza B

Influenza B viruses are not divided into subtypes but are classified into two lineages: B/Yamagata and B/Victoria. These viruses primarily infect humans and are less genetically diverse than influenza A viruses. Although they do not cause pandemics, influenza B viruses can contribute to seasonal flu epidemics.

Influenza C

Influenza C viruses cause mild respiratory illnesses and are not considered a significant public health concern. They do not cause epidemics or pandemics.

Influenza D

Influenza D viruses primarily infect cattle and are not known to infect humans. They are not a cause of concern for human health.

Diagnosis of Influenza Virus

Diagnosing influenza involves a combination of clinical evaluation and laboratory testing. Essential diagnostic methods include:

Rapid Influenza Diagnostic Tests (RIDTs)

RIDTs detect influenza virus antigens in respiratory specimens and provide results within 10-15 minutes. However, they are less accurate than other methods and can produce false-negative results.

Rapid Molecular Assays

These tests detect the genetic material of the influenza virus and are more accurate than RIDTs. They provide results in 15-20 minutes and are increasingly used in clinical settings.

RT-PCR (Reverse Transcription Polymerase Chain Reaction)

RT-PCR is the gold standard for influenza diagnosis. It is susceptible and specific, capable of detecting and differentiating between influenza A and B viruses. However, it requires specialized laboratory equipment and trained personnel, making it less accessible for routine use.

Viral Culture

Though less commonly used due to the time required for results (several days), viral culture remains a valuable method for identifying influenza virus strains and subtypes.

Treatment of Influenza Virus

Treatment for influenza focuses on relieving symptoms and may include antiviral medications. Key treatment options include:

Antiviral Medications

Antiviral drugs can lessen symptoms and shorten the duration of illness. Common antivirals for influenza include:

• Oseltamivir (Tamiflu): Available in pill or liquid form.
• Zanamivir (Relenza): Administered via inhaler.
• Peramivir (Rapivab): Given intravenously.
• Baloxavir Marboxil (Xofluza): A single-dose oral medication.

Antivirals are most effective when started within 48 hours of symptom onset.

Symptomatic Treatment

Over-the-counter medications can help alleviate symptoms such as fever, muscle aches, and congestion. These include:

• Analgesics: Acetaminophen or ibuprofen for pain and fever.
• Decongestants: To relieve nasal congestion.
• Cough Suppressants: To reduce coughing.

Home Care

Rest, hydration, and maintaining a comfortable environment can aid recovery. To prevent the spread of the virus, it's important to avoid close contact with others.

Influenza Virus Vaccine

Vaccination is the most effective way to prevent influenza. The influenza vaccine is updated annually to match circulating strains and is recommended for everyone aged six months and older. Types of influenza vaccines include:

Inactivated Influenza Vaccine (IIV)

Administered via injection, this vaccine contains killed virus particles and is safe for use in most people, including pregnant women and those with chronic health conditions.

Live Attenuated Influenza Vaccine (LAIV)

Administered via nasal spray, this vaccine contains weakened live virus and is suitable for healthy individuals aged 2-49 years who are not pregnant.

Recombinant Influenza Vaccine (RIV)

This egg-free vaccine is produced using recombinant technology and is an option for individuals with egg allergies.

Conclusion

Understanding the influenza virus, its types, symptoms, causes, diagnosis, treatment, and prevention strategies is crucial for managing and mitigating its impact. By staying informed and taking appropriate measures, we can reduce the burden of influenza on public health and improve outcomes for those affected. Regular vaccination, good hygiene practices, and timely medical intervention remain our best defences against this pervasive virus.

Frequently Asked Questions