Influenza is caused by a virus.

Influenza, commonly known as the flu, is a highly contagious respiratory illness that affects millions of people worldwide. It is caused by the influenza virus, which belongs to the Orthomyxoviridae family. The virus can infect both humans and animals, and it is responsible for causing annual flu outbreaks.

There are several types of influenza viruses, including influenza A, B, C, and D. Influenza A and B viruses are the most common causes of seasonal flu epidemics. Influenza C viruses cause mild respiratory illness, while influenza D viruses primarily affect cattle.

How the influenza virus spreads:
The influenza virus spreads from person to person through respiratory droplets when an infected person coughs, sneezes, or talks. These droplets can be inhaled by others or land on surfaces, where they can survive for a short period of time. When a person touches an infected surface and then touches their mouth, nose, or eyes, they can become infected.

Symptoms of influenza:
Influenza symptoms typically appear 1-4 days after infection and can range from mild to severe. Common symptoms include:

- High fever
- Body aches
- Fatigue
- Headache
- Sore throat
- Cough
- Runny or stuffy nose

Treatment and prevention:
There is no cure for influenza, but several measures can be taken to relieve symptoms and prevent its spread. Treatment options include resting, staying hydrated, and taking over-the-counter medications to reduce fever and alleviate symptoms.

To prevent influenza, getting an annual flu vaccine is highly recommended. The vaccine stimulates the immune system to produce antibodies that protect against the specific strains of the virus included in the vaccine. Additionally, practicing good hygiene, such as washing hands frequently, covering the mouth and nose when coughing or sneezing, and avoiding close contact with sick individuals, can help reduce the risk of infection.

Conclusion:
Influenza is caused by a virus, specifically the influenza virus. It is a highly contagious respiratory illness that spreads from person to person through respiratory droplets. Symptoms can range from mild to severe, and treatment focuses on relieving symptoms and preventing the spread of the virus through vaccination and good hygiene practices.

But, edurev is saying that it is the b one.