Resurgence of Influenza Cases

• Context (IE): The National Centre for Disease Control (NCDC) has reported a resurgence of Influenza cases in several Indian states.
• Seasonal influenza (the flu) is an acute respiratory infection caused by influenza viruses.
• It is highly contagious, affects the respiratory system, including the nose, throat and lungs, and is common in all parts of the world.
• Transmission: Droplets containing viruses in the air, contaminated hands, etc.
• Factors like high population density, poor hygiene practices, weather conducive to the survival and spread of the virus and low vaccination rates increase the risk of flu transmission.
• Symptoms: Sudden onset of fever, cough (usually dry), headache, muscle and joint pain, severe malaise (feeling unwell), sore throat and a runny nose.
• Most people recover from fever and other symptoms within a week without requiring medical attention. But influenza can cause severe illness or deaths, especially in people at high risk.
• In India, the most prevalent subtypes are influenza A (H1N1), A (H3N2), and influenza B viruses. 

Types of Influenza Viruses

Influenza A Virus (IAV)

• Primary Source: Aquatic birds (wild birds).
• Widespread: IAV is also found in various mammals, including humans and pigs.
• Clinical Impact: Influenza A viruses cause seasonal epidemics (commonly known as flu seasons) almost every winter.
• IAV is the only influenza virus known to cause global epidemics (pandemics) of flu disease.

Pandemics occur when a new and different IAV emerges, efficiently spreads among people, and encounters little or no existing immunity.

Influenza B Virus (IBV)

• IBV primarily infects humans.
• Severity: While less severe than IAV, IBV still contributes to respiratory infections.
• Vaccine Coverage: Seasonal flu vaccines target both IAV and IBV strains.

Influenza C Virus (ICV)

• ICV infections generally cause mild illness.
• ICV is not thought to cause human epidemics.

Influenza D Virus (IDV)

• IDV primarily affects cattle and pigs.
• Although found in animals, IDV is not known to infect humans and cause illness.

Naming Influenza Virus