The replication cycle of the influenza virus consists of six stages:
1. **Attachment**: The virus binds to receptors on a target epithelial cell.
2. **Penetration**: The host cell engulfs the virus through endocytosis, enclosing it in a vacuole.
3. **Uncoating**: The viral envelope and contents are released from the vacuole.
4. **Biosynthesis**: The viral RNA enters the nucleus, where it is replicated by RNA polymerase.
5. **Assembly**: New viral particles are assembled.
6. **Release**: The newly formed viral particles exit into the extracellular fluid, leaving the host cell alive to continue virus production.

Steps of Influenza Infection

Influenza, commonly known as the flu, is a common viral disease caused by an orthomyxovirus that primarily affects the upper respiratory tract.

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The respiratory tract can be infected by many different viruses, which cause many different diseases. The diseases that can be caused by viruses include:
 - Common Cold
 - Influenza
 - Viral Pneumonia
 - SARS
 - MERS
 - Measles (Rubeola)
 - Rubella (German Measles)
 - Chickenpox and Shingles

The Different Viral Infections of the Respiratory System

https://openstax.org/details/books/microbiology/

Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

OpenStax Microbiology Textbook

Influenza

Viral Pneumonia can be caused by several viruses and can lead to pneumonia in children and the elderly. The most common sources of viral pneumonia are adenoviruses, influenza viruses, parainfluenza viruses, and respiratory syncytial viruses.

Viral Pneumonia

Severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) are two acute respiratory infections caused by coronaviruses. These are thought to be zoonotic infections.

SARS and MERS

The Measles (Rubeola) is caused by the measles virus (MeV.) This is a major cause of childhood mortality worldwide. Although vaccination efforts have greatly reduced the incidence of measles in much of the world, epidemics are still common in unvaccinated populations in certain countries.

Measles (Rubeola)

Rubella, (German measles) is caused by rubella virus and is a relatively mild viral disease that produces a rash somewhat like that caused by the measles, even though the two diseases are unrelated.

Rubella (German Measles)

Chickenpox, also known as varicella, was once a common viral childhood disease. The causative agent is the varicella-zoster virus, and is a member of the herpesvirus family. This virus causes 2 diseases throughout life:
 - Chickenpox
 - Shingles

Chickenpox and Shingles

The common cold is a generic term for a variety of mild viral infections of the respiratory system. More than 200 different viruses are known to cause the common cold. The most common groups of cold viruses include rhinoviruses, coronaviruses, and adenoviruses.

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