Influenza, commonly called the flu, is a contagious respiratory illness caused by influenza viruses. It can range from mild to severe and affects the nose, throat, and lungs. In serious cases, especially in the very young, elderly, or those with underlying health conditions, it can lead to hospitalization or death.
🦠 Types of Influenza Viruses
Influenza A
Most severe form; causes pandemics.
Infects humans and animals (e.g., birds, pigs).
Subtypes are based on hemagglutinin (H) and neuraminidase (N) proteins (e.g., H1N1, H3N2).
Influenza B
Milder than type A but can still cause outbreaks.
Affects only humans.
No subtypes, but has two lineages: B/Yamagata and B/Victoria.
Influenza C
Causes mild illness, mostly in children.
Rarely causes epidemics.
Influenza D
Found in cattle; not known to infect humans.
🤧 Symptoms
Fever or chills
Cough
Sore throat
Runny or stuffy nose
Muscle/body aches
Fatigue
Headache
Sometimes vomiting or diarrhea (more common in children)
🔄 Transmission
Spread mainly by droplets when an infected person coughs, sneezes, or talks.
Can also spread by touching surfaces contaminated with the virus and then touching the mouth, nose, or eyes.
🧪 Diagnosis
Rapid influenza diagnostic tests (RIDTs)
PCR tests (more accurate)
Based on symptoms and season (flu season: fall through spring in most regions)
💊 Treatment
Antiviral medications (most effective if started within 48 hours):
Oseltamivir (Tamiflu)
Zanamivir (Relenza)
Baloxavir (Xofluza)
Most people recover with rest, fluids, and fever reducers (acetaminophen, ibuprofen).
💉 Prevention
Annual flu vaccine (updated each year to match circulating strains)
Good hygiene (handwashing, covering coughs/sneezes)
Avoiding contact with sick individuals
Wearing masks in high-risk settings during flu season
🧬 Mutation and Evolution
Influenza viruses constantly change:
Antigenic drift: Small changes that cause seasonal flu.
Antigenic shift: Major changes (usually in type A) that can cause pandemics.