Influenza or Flu

Influenza is a highly contagious viral infection caused by influenza viruses. Influenza infectious disease attacks the respiratory system:  nose, throat, and lungs. Influenza is commonly called the flu.

The symptoms Influenza infections range from mild to severe, often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. The symptoms of Influenza typically begin 1 -4 days after exposure to the Influenza virus.

Influenza infection occurs most often during the winter season and easily spreads from person to person.  Young children under the age of 5 years are at higher risk of developing flu, especially those under 6 months and adults older than age 65 years.

Types of Influenza

Influenza has four viral subtypes –

1. Influenza A virus (IAV); include H1N1, H5N1, and H3N2

2. Influenza B virus (IBV)

3. Influenza C virus (ICV)

4. Influenza D virus (IDV)

Influenza A viruses infects humans and many different animals.

Influenza B virus (IBV) and Influenza C virus (ICV) primarily infect the humans; ICV causes a mild infection, primarily in children.

Influenza A virus (IAV) and Influenza B virus (IBV) circulate in humans and cause seasonal epidemics disease throughout the world.

Influenza D virus is found in cattle, swine, and pigs.

Epidemiology Triad

Agent – influenza is caused due to the influenza viruses. RNA virus of Orthomyxoviridae family.

Human, animals and birds such as swine, dogs, horses, wild birds etc. are reservoir of infection. Secretion of present in the respiratory tract of a case of influenza are infectious especially nasopharyngeal secretions.

Host – Seasonal influenza tends to target children 6 months to 5 years old children, mostly children under 18 months. Affect adults 65 years of age or older patient with diabetes, heart disease, kidney or respiratory disease.

Occurs in all age group and both sexes.

Environment– Influenza occurs during winter and rainy months.

Overcrowding places

Mode of Transmission

Portal of entry – Respiratory infection

In humans, influenza viruses are primarily spread through respiratory droplets, coughing and sneezing and also transmitted through aerosols, intermediate objects, surfaces contaminated by the virus.

1. Droplet nuclei

2. Droplet infection

3.  Spread by personal contact

4. Spread by air in droplets when people with the infection coughs, sneezes, or talks.

Incubation Period

The incubation period of influenza viruses is 1 – 4 days, most commonly 1 – 2 days (18 to 72 hours).

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Pathophysiology of Influenza Infection

1. Infection occurs through Respiratory tract

2. Influenza virus attachment to cell membrane

3. Influenza virus replication, production of cytokines factor

4. Airway inflammation

5. Infecting epithelial cells in the respiratory tract

 6. Destruction of epithelial cells from nasopharynx to alveoli

6. Systemic body reaction; fever, muscle pain

Clinical Features of Influenza

Common signs and symptoms of the flu include –

1. Fever

2. Aching muscles

3. Chills and sweats

4. Headache

5. Dry, persistent cough

6. Shortness of breath

7. Tiredness and weakness

8. Runny or stuffy nose

9. Sore throat

10. Eye pain

11. Vomiting and diarrhoea (more common in children than adults)

Seasonal influenza characterized by a sudden onset of –

Fever, cough (usually dry), headache, muscle and joint pain, severe malaise, sore throat, runny nose

Emergency signs and symptoms can include –

1. Difficulty breathing

2. Chest pain

3. Blue lips

4. Dehydration

5. Severe weakness

6. Severe muscle pain

7. Seizures

8. Worsening of existing medical conditions

Influenza may develop into Pneumoniadisease that can be caused by the virus or often followed by bacterial infection.

Other complications of influenza or Flu infection include – Acute respiratory distress syndrome, encephalitis, meningitis and worsening of the pre-existing conditions of health problems such as asthma and cardiovascular disease.

Laboratory Investigation

1. Virus is detected by the indirect fluorescent antibody test (IFA)

2. Serological examination

3. Detection of influenza – Sspecific RNA by RT- PCR (Reverse transcription polymerase chain reaction)

4. Rapid influenza test

5. Nucleic acid-based tests (NATs) – To detect viral nucleic acid

Flu Risk Factors

Higher risk of developing flu include – 

1. Young children under age of 5 years, and especially children under 6 months

2. Adults who older than age of 65 years

3. Person is in under long-term care facilities

4. Pregnant women and women after giving birth up to two weeks

5. Individual with weakened immune system

6. People with certain chronic illnesses at high risk such as; asthma, kidney disease, heart disease, liver disease, COPD, bronchiectasis and diabetes

7. People with diseases (HIV, AIDS) or treatments (steroids, chemotherapy) that suppress immunity

8. Children and adolescents who are receiving long-term aspirin therapy

Causes of Flu

Influenza viruses cause the flu that infects the nose, throat, and lungs. These viruses are transmitted when people with flu cough, sneeze, talk.  Droplets with the virus spread into the air and potentially enter into the mouths or noses of nearby people. A person can also get flu by touching an infected surface or object virus on it and enter when touching own mouth, eyes, or nose.

Prevention of influenza Diseases

1. Frequent hand washing – Frequent hand washing with soap and water, using alcohol-based hand sanitizers reducing the spread of influenza and not touching own eyes, nose, and mouth with hands.

2. Covering own mouth and nose when coughing and sneezing reduce transmission.

3. WHO recommends Annual vaccination requires protecting against influenza.

Annual vaccination is the primary way and most effective to prevent influenza infection and influenza-associated disease and complications, especially for those people who at high-risk groups.

1. Vaccines– killed vaccines

Vaccine                        Dose                Age                 Route  

killed vaccine            1.5ml            6 months            subcutaneous route

Note– The inactivated influenza vaccine can be given to all pregnant women during any trimester.

2. Live attenuated vaccine – Administration as nose drops into respiratory tract.

3. Other vaccines –  Recombinant vaccine

4. Antiviral drugs –  Rimantadine and Amantadine drug as prophylaxis

5. Avoidance of overcrowded place

6. Good ventilation in a public building

Treatment of Influenza

Treatment of influenza includes –

1.  Anti-fever medications such as acetaminophen and ibuprofen

 2. Adequate fluid intake to avoid dehydration

3. Cough drops and throat sprays may be beneficial for sore throat

Note – Aspirin is not recommended to treat influenza infection in children due to an increased risk of developing Reye syndrome (swelling in the brain and liver damage).

Corticosteroids are not recommended except when treating septic shock or an underlying medical condition, such as chronic obstructive pulmonary disease  (COPD) or asthma exacerbation (asthma attack). corticosteroids treatment may not be beneficial for patients with severe influenza and may even increase mortality.

Antiviral Chemoprophylaxis

 

Post-exposure chemoprophylaxis of influenza infection can be prevented or reduced in severity by with the antiviral drugs Oseltamivir is taken within 48 hours of contact with a confirmed or suspected influenza case and Zanamivir within 36 hours.

Complications of Influenza

1. Asthma flare-ups

2. Acute respiratory distress syndrome

3. Pneumonia

4. Chest discomfort

5. Bronchitis

6 Heart problems

7. Ear infections

FAQ‘s on Influenza

1. What Are the Symptoms of Influenza?

The symptoms  of Flu often appear suddenly. Symptoms of influenza can include- sudden onset of high fever, headache, muscle aches and joint pain, C]cough (usually dry), chills, sore throat, nasal congestion and runny nose, stomach symptoms such as nausea, vomiting or diarrhea may occur but are more common in children than adults.

2. What are Types of Influenza?

Influenza virus has four viral subtypes –

1. Influenza A virus (IAV)

2. Influenza B virus (IBV)

3. Influenza C virus (ICV)

4. Influenza D virus (IDV)

3. What is the difference between flu and influenza?

Influenza is a viral infection that attacks your respiratory system; nose, throat, and lungs. Influenza is commonly called the flu, but it is not the same as stomach “flu” viruses that cause diarrhea and vomiting.

4. What are differences between a common cold and influenza (flu)?

Many cold and flu have similar symptoms. Both common colds and flu are caused by viruses. The symptoms of influenza often hit suddenly and cause become weaker and weaker and cause dry cough and fatigue. Signs of influenza is getting worse include increasing degree of fever, and shortness of breath.

 

5. Can get medicine for influenza (flu)?

Antiviral drugs for influenza (flu virus) include Oseltamivir phosphate, Zanamivir, Peramivir, and Baloxavir.

Take acetaminophen to reduce fever and relieve muscle aches.

6.  What complications are associated with influenza (flu)?

Infections from bacteria are more occur when having influenza infection. Treat these bacterial infections with antibiotic drugs. Common secondary infections include – bacterial pneumonia, ear infections, sinus infections.