What Is a Viral Disease?

A viral disease is an illness caused by infection with a:

virus.

Viruses are extremely small infectious agents. Unlike bacteria, viruses are not cells and cannot reproduce independently.

To make new viruses, they must infect a:

host cell.

Examples of viral diseases include:

• influenza
• COVID-19
• measles
• chickenpox
• dengue
• hepatitis B
• HIV infection and AIDS
• polio
• rabies

Different viruses infect different tissues and spread through different routes.

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What Is a Virus?

A virus consists of genetic material surrounded by a protective:

protein coat.

The genetic material may be:

DNA or RNA.

The protein coat is called a:

capsid.

Some viruses also possess an outer:

lipid envelope.

Viruses do not have the complete cellular machinery required to reproduce independently.

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Basic Virus Structure

A virus may contain:

Genetic material

DNA or RNA containing instructions for producing new virus particles.

Capsid

A protein coat surrounding and protecting the genetic material.

Envelope

Some viruses possess a lipid membrane surrounding the capsid.

Surface proteins

Proteins that can help a virus recognize and attach to particular host cells.

Different viruses have different shapes and structures.

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Are Viruses Living?

Viruses have some characteristics associated with living organisms, such as:

• genetic material
• ability to evolve
• ability to reproduce when inside suitable cells

However, they cannot independently:

• reproduce
• perform cellular metabolism
• maintain normal cellular functions

For this reason, viruses are generally described as:

non-cellular infectious agents,

rather than complete living cells.

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Viruses Need Host Cells

A virus cannot simply divide like a bacterium.

Instead, it must infect a:

host cell.

The virus uses the host cell's machinery and resources to produce:

viral components.

These components are assembled into new virus particles.

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Viral Replication

A simplified viral replication cycle is:

attachment → entry → replication and protein production → assembly → release

The exact process varies between different viruses.

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Step 1: Attachment

A virus first attaches to specific molecules on the surface of a:

host cell.

These molecules are often called:

receptors.

The interaction between viral surface proteins and cellular receptors helps determine which cells the virus can infect.

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Step 2: Entry

The virus or its genetic material enters the:

host cell.

Different viruses use different mechanisms.

Some viruses enter the cell inside membrane-bound structures.

Others deliver their genetic material into the cell.

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Step 3: Viral Replication

Once inside the cell, viral genetic information directs the production of:

• new viral genetic material
• viral proteins

The virus depends heavily on the host cell's:

machinery.

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Step 4: Assembly

New viral components are assembled into:

virus particles.

Each new particle contains viral genetic material surrounded by the appropriate structural proteins.

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Step 5: Release

New viruses leave the infected cell.

Some viruses cause the cell to:

burst.

Others leave by budding through the cell membrane.

The released viruses can then infect:

other cells.

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How Viral Infections Cause Disease

Viral infections can cause disease in several ways.

Viruses may:

• damage infected cells
• destroy cells during replication
• interfere with normal cell functions
• trigger inflammation
• produce strong immune responses
• cause long-term changes in infected tissues

The exact mechanism depends on the:

virus.

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Viral Infections vs Bacterial Infections

Viruses and bacteria are fundamentally different.

Viruses

• are not cells
• contain DNA or RNA
• require host cells for replication
• are generally much smaller than bacteria
• are not treated with antibiotics

Bacteria

• are living prokaryotic cells
• contain DNA
• contain ribosomes
• can reproduce independently under suitable conditions
• reproduce mainly by binary fission
• some bacterial infections can be treated with antibiotics

This difference is extremely important when choosing:

treatment.

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Antibiotics and Viral Disease

Antibiotics do not treat viral infections.

Antibiotics target structures or processes found in bacteria, such as:

• bacterial cell walls
• bacterial ribosomes
• particular bacterial metabolic pathways

Viruses do not possess these structures in the same way.

Therefore, using antibiotics against a purely viral infection does not eliminate the virus.

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Can Antibiotics Ever Be Used During a Viral Illness?

Sometimes a viral infection is followed by a separate:

bacterial infection.

In that situation, antibiotics may be used to treat the bacterial infection.

The antibiotics are treating:

the bacteria, not the virus.

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Influenza

Influenza, commonly called the flu, is caused by:

influenza viruses.

It primarily infects the respiratory system.

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Influenza Symptoms

Common symptoms can include:

• fever
• cough
• sore throat
• muscle aches
• headache
• fatigue

Some people develop complications, particularly those at greater risk of severe illness.

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Influenza Transmission

Influenza spreads mainly through:

respiratory transmission.

Infected people release virus-containing respiratory particles when they:

• breathe
• talk
• cough
• sneeze

Transmission is more likely when susceptible people have sufficient exposure to infectious particles.

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Managing Influenza

Management may include:

• rest
• fluids
• symptom management
• antiviral medication in appropriate situations

Vaccination can reduce the risk of influenza and its complications.

Influenza vaccines are updated regularly because influenza viruses:

change over time.

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COVID-19

COVID-19 is caused by:

SARS-CoV-2.

SARS-CoV-2 is a:

coronavirus.

It primarily spreads through infectious respiratory particles.

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COVID-19 Symptoms

Symptoms vary widely and may include:

• fever
• cough
• sore throat
• fatigue
• headache
• muscle aches
• changes in smell or taste

Some infections produce few or no noticeable symptoms.

Others can cause serious disease.

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Preventing Respiratory Viral Disease

Depending on the virus and situation, strategies can include:

• vaccination
• good ventilation
• staying away from others while infectious
• respiratory hygiene
• appropriate mask use in higher-risk settings
• hand hygiene

Effective prevention focuses on the virus's actual:

transmission route.

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Measles

Measles is caused by the measles virus.

It is a highly transmissible respiratory viral disease.

Symptoms commonly include:

• fever
• cough
• runny nose
• red eyes
• characteristic rash

Measles can sometimes cause serious complications.

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Measles Prevention

The most important method of preventing measles is:

vaccination.

The measles-containing vaccine produces immune memory that allows the immune system to respond much more effectively if the virus is encountered later.

High vaccination coverage also reduces opportunities for the virus to spread through:

populations.

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Chickenpox

Chickenpox is caused by:

varicella-zoster virus.

Common symptoms include:

• fever
• tiredness
• an itchy blister-like rash

After the initial infection, the virus can remain dormant in nerve tissue.

Years later it can sometimes reactivate and cause:

shingles.

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Dengue

Dengue is a viral disease caused by dengue viruses.

It is transmitted mainly by infected:

Aedes mosquitoes.

The mosquito is the:

vector.

The dengue virus is the:

pathogen.

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Dengue Transmission

The basic transmission cycle includes:

infected human → mosquito → another human

A mosquito can acquire dengue virus when feeding on an infected person.

After the virus develops within the mosquito, the mosquito can transmit it during a later:

bite.

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Dengue Prevention

Because mosquitoes transmit dengue, prevention focuses heavily on reducing contact with:

Aedes mosquitoes.

Strategies can include:

• removing standing water where mosquitoes breed
• using insect repellent
• using screens
• wearing protective clothing
• mosquito-control programs

This demonstrates why prevention strategies should match the pathogen's:

mode of transmission.

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HIV

HIV stands for:

Human Immunodeficiency Virus.

HIV infects important cells of the:

immune system.

Without effective treatment, the immune system can become progressively damaged.

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HIV and AIDS

HIV and AIDS are not the same thing.

HIV is the virus.

AIDS is a late stage of HIV infection characterized by severe immune-system damage and particular clinical conditions.

Modern treatment can greatly reduce the likelihood that HIV infection progresses to:

AIDS.

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HIV Transmission

HIV can be transmitted through certain body fluids.

Important routes include:

• sexual transmission
• blood exposure
• sharing contaminated needles
• transmission during pregnancy, birth, or breastfeeding

HIV is not spread through ordinary casual contact such as:

• shaking hands
• sharing a room
• hugging
• ordinary social contact

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Managing HIV

HIV can be managed using:

antiretroviral therapy, or ART.

ART uses medicines that interfere with different stages of the HIV replication cycle.

Effective treatment can reduce the amount of virus in the body to very low levels and allows many people with HIV to live long, healthy lives.

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Hepatitis B

Hepatitis B is caused by the hepatitis B virus.

It primarily affects the:

liver.

Transmission can occur through:

• blood
• sexual contact
• transmission from parent to child during birth

Some infections become chronic.

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Preventing Hepatitis B

An effective:

vaccine

is available against hepatitis B.

Other prevention measures depend on reducing exposure to infected blood and body fluids.

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Polio

Polio, or poliomyelitis, is caused by:

poliovirus.

Most infections do not cause paralysis, but in a small proportion of cases the virus can affect the nervous system and cause:

paralysis.

Vaccination has dramatically reduced polio worldwide.

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Rabies

Rabies is a viral disease affecting the:

nervous system.

Humans usually become infected through saliva from an infected animal, often through a:

bite.

Once clinical symptoms appear, rabies is almost always fatal.

However, prompt post-exposure medical treatment can prevent disease after many exposures.

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Different Viruses Spread Differently

Viruses can spread through many routes.

These include:

• respiratory transmission
• direct contact
• fecal-oral transmission
• blood
• sexual contact
• vectors
• animal bites
• parent-to-child transmission

There is no single transmission route used by all:

viruses.

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Respiratory Transmission

Viruses such as influenza viruses and SARS-CoV-2 can spread through:

respiratory particles.

Transmission may be influenced by:

• proximity
• duration of exposure
• ventilation
• number of infectious people
• population immunity

Indoor environments with poor ventilation can increase opportunities for transmission.

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Fecal-Oral Transmission

Some viruses can spread through the:

fecal-oral route.

Examples include:

• norovirus
• poliovirus
• hepatitis A virus

Good sanitation, clean water, food hygiene, and handwashing can reduce this type of transmission.

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Bloodborne Transmission

Some viruses can spread through:

blood.

Examples include:

• HIV
• hepatitis B virus
• hepatitis C virus

Prevention can include safe medical practices and avoiding shared contaminated needles.

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Vector-Borne Transmission

Some viruses depend on:

vectors.

Examples include:

Dengue virus → Aedes mosquito

Yellow fever virus → mosquitoes

West Nile virus → mosquitoes

Controlling vectors can therefore reduce transmission.

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How Viruses Spread Through Populations

For a virus to spread through a population, it must successfully move from infected hosts to:

susceptible hosts.

Population spread is affected by:

• transmission efficiency
• contact patterns
• infectious period
• population density
• immunity
• vaccination
• environmental conditions
• human behavior
• vector populations

These factors interact.

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Susceptible Hosts

A susceptible host is an individual who can become infected when exposed to a particular virus.

Susceptibility can be influenced by:

• previous infection
• vaccination
• immune function
• age
• characteristics of the virus

A virus spreads more easily when it frequently encounters susceptible:

hosts.

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Incubation Period

The incubation period is the time between:

infection and the appearance of symptoms.

Different viruses have different incubation periods.

For some viral diseases, a person may be infectious before noticeable symptoms appear.

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Asymptomatic Infection

Some viral infections produce no noticeable:

symptoms.

This is called an:

asymptomatic infection.

Depending on the virus, an asymptomatic person may still be able to transmit the infection.

This can make disease control more difficult.

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The Infectious Period

The infectious period is the time during which an infected person can transmit a virus to:

others.

The infectious period may begin:

• before symptoms
• during symptoms
• sometimes after symptoms improve

The pattern depends on the particular virus.

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Outbreaks

An outbreak occurs when cases of a disease increase above what is normally expected in a particular place or group.

If a virus reaches many susceptible people and transmission continues, the number of cases can:

increase.

Public-health measures aim to interrupt transmission.

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Epidemics

An epidemic is an occurrence of disease cases above expected levels in a population or region.

The exact use of the term depends on:

context.

An epidemic may involve a particular city, region, country, or population.

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Pandemics

A pandemic is an epidemic that spreads across multiple countries or continents and affects large numbers of people.

The word describes the:

geographic spread of disease.

It does not by itself describe how severe the disease is for each infected person.

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Immunity and Viral Spread

The immune system can develop memory after:

• some natural infections
• vaccination

Immune memory may allow a faster response during later exposure.

Depending on the virus, immunity may reduce:

• infection
• disease severity
• infectiousness
• duration of infection

The strength and duration of protection vary between viruses.

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Vaccines

A vaccine exposes the immune system to an antigen, or instructions for producing an antigen, in a controlled way.

This stimulates the development of:

immune memory.

If the actual virus is encountered later, the immune system can respond more rapidly.

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Vaccines Do Not Directly Kill Viruses

Vaccines primarily work by preparing the:

immune system.

They are mainly:

preventive.

They help the body respond more effectively if exposure occurs later.

This is different from a medicine used to treat an infection that has already become established.

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Antiviral Medicines

Antiviral medicines interfere with stages of viral replication.

Depending on the virus, they may interfere with:

• viral entry
• genome replication
• viral enzymes
• assembly
• release

Antivirals are usually specific to particular viruses or groups of viruses.

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Why Antivirals Are Challenging to Develop

Viruses reproduce inside:

host cells.

This makes treatment challenging because a medicine must interfere with the virus without causing unacceptable damage to the host's own cells.

Viruses can also:

mutate and evolve.

This may lead to antiviral resistance.

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Antiviral Treatment for Influenza

Certain antiviral medicines can be used against:

influenza.

They may reduce the duration or severity of illness when used appropriately, particularly when started early.

They do not replace:

vaccination.

Prevention and treatment serve different purposes.

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Antiretroviral Therapy

HIV is treated using combinations of:

antiretroviral medicines.

Different drugs target different stages of HIV replication.

Using combinations makes it more difficult for the virus to develop resistance.

Treatment can suppress viral replication very effectively.

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Supportive Care

Many viral illnesses are managed partly through:

supportive care.

Supportive care helps the body while the immune system responds.

Depending on the illness, this may include:

• rest
• fluids
• symptom management
• oxygen or other medical support in severe cases

Supportive care does not necessarily directly destroy the virus.

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The Immune System

For many viral infections, the body's:

immune system

is responsible for eventually controlling or eliminating the infection.

Important components include:

• innate immune defenses
• antibodies
• B cells
• T cells
• memory cells

The immune response can also contribute to some disease symptoms.

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Prevention vs Treatment

These two ideas should not be confused.

Prevention

Occurs mainly:

before infection or exposure leads to disease.

Examples:

• vaccination
• ventilation
• hand hygiene
• vector control
• safer sexual practices

Treatment

Occurs:

after infection has occurred.

Examples:

• antiviral medicines
• supportive care
• antiretroviral therapy

Some interventions can also be used shortly after exposure to prevent disease from developing.

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Prevention Must Match Transmission

The best prevention strategy depends on how the virus:

spreads.

For influenza:

vaccination + respiratory precautions

For dengue:

mosquito control + protection from mosquito bites

For hepatitis B:

vaccination + prevention of blood/body-fluid exposure

For HIV:

prevention of relevant blood and sexual exposure + effective medical prevention strategies

For rabies:

avoiding animal exposure + urgent post-exposure treatment when needed

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Comparing Influenza and Dengue

Influenza

Pathogen:

influenza virus

Transmission:

respiratory

Major prevention:

vaccination and reducing respiratory exposure

Dengue

Pathogen:

dengue virus

Transmission:

mosquito vector

Major prevention:

reducing mosquito exposure and controlling mosquito populations

The diseases are both viral, but their prevention strategies differ because their:

transmission routes differ.

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Comparing Measles and HIV

Measles

Main transmission:

respiratory

Important prevention:

vaccination

HIV

Main transmission:

specific body fluids

Important prevention:

reducing relevant exposure and using effective biomedical prevention strategies

Again, understanding transmission determines appropriate prevention.

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Viral Mutation

Viruses can acquire changes in their genetic material called:

mutations.

Most mutations do not automatically make a virus more dangerous.

However, some mutations can alter characteristics such as:

• transmissibility
• immune recognition
• drug susceptibility
• interaction with host cells

Evolution can therefore influence viral populations over time.

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Natural Selection in Viruses

Suppose a viral population contains genetic variation.

If environmental conditions favor one variant, that variant may reproduce more successfully.

Over generations:

advantageous inherited variants can become more common.

This is:

natural selection.

Viruses therefore evolve, just as other biological populations do.

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Antiviral Resistance

If a mutation allows a virus to reproduce despite an antiviral drug, the drug creates:

selection pressure.

Susceptible viruses are inhibited more strongly.

Resistant variants may continue reproducing.

Over time, resistance can become more common.

This is one reason antiviral medicines must be used:

appropriately.

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Why Prevention Matters

Preventing viral disease can:

• protect individuals
• reduce severe illness
• reduce transmission
• protect vulnerable populations
• reduce pressure on healthcare systems
• reduce opportunities for some viruses to spread

Preventing infection can be especially important when effective treatments are limited.

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Layered Prevention

Sometimes several prevention strategies are combined.

For respiratory viral disease, this might include:

vaccination + ventilation + staying away from others while infectious + appropriate respiratory precautions

Each layer may reduce some risk.

Together they can provide greater protection than relying on only one strategy.

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Worked Example 1

A pathogen contains RNA inside a protein coat and can reproduce only inside host cells.

What type of pathogen is it?

A:

virus.

The dependence on host cells is a major characteristic of viruses.

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Worked Example 2

A patient has influenza.

Would an antibiotic kill the influenza virus?

No.

Influenza is caused by a virus.

Antibiotics target:

bacteria.

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Worked Example 3

A virus spreads when infected mosquitoes bite people.

What type of transmission is occurring?

Vector-borne transmission.

A prevention strategy should therefore include:

reducing contact with the vector.

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Worked Example 4

A vaccine causes the immune system to produce memory cells.

Is this prevention or treatment?

Primarily:

prevention.

The immune system is being prepared before future exposure.

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Worked Example 5

A medicine blocks an enzyme needed for a virus to reproduce.

What type of medicine is this?

An:

antiviral.

It interferes with viral replication.

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Worked Example 6

Two viral diseases are prevented using completely different methods.

Why?

Different viruses can have different:

transmission routes.

Prevention should target the way each virus spreads.

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Worked Example 7

A person is infected but has no symptoms.

Can the person necessarily be considered non-infectious?

No.

For some viral infections, asymptomatic people can still transmit the virus.

Infectiousness depends on the particular virus and stage of infection.

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Worked Example 8

A viral disease is spreading rapidly in a poorly ventilated indoor environment.

What factor could be contributing to transmission?

If the virus spreads through respiratory particles:

poor ventilation can allow infectious particles to accumulate.

Improving ventilation may reduce exposure.

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Comparing Viral and Bacterial Disease

Structure

Virus:

non-cellular

Bacterium:

prokaryotic cell

Reproduction

Virus:

requires a host cell

Bacterium:

can reproduce independently under suitable conditions

Genetic material

Virus:

DNA or RNA

Bacterium:

DNA

Ribosomes

Virus:

absent

Bacterium:

present

Antibiotics

Virus:

not effective

Bacterium:

may be effective depending on susceptibility

Specialized medicines

Virus:

antivirals may be available

Bacterium:

antibiotics may be available

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Common Mistake: Viruses Are Tiny Bacteria

Viruses are not bacteria.

They have fundamentally different:

• structures
• replication mechanisms
• biological properties

A virus is:

not a cell.

A bacterium is:

a living prokaryotic cell.

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Common Mistake: Antibiotics Treat Viral Disease

Antibiotics do not treat viral infections.

Unnecessary antibiotic use can contribute to:

antibiotic resistance in bacteria.

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Common Mistake: Every Virus Has an Antiviral Treatment

Many viral infections do not have a specific antiviral medicine.

Management may rely on:

• immune response
• supportive care
• prevention

The available treatment depends on the particular virus.

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Common Mistake: Vaccines Cure Existing Viral Infections

Vaccines are primarily designed to:

prevent disease or reduce its impact by preparing the immune system.

They are not generally treatments that eliminate an already established infection.

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Common Mistake: All Viruses Spread Through the Air

Viruses use many different transmission routes.

Examples include:

Influenza → respiratory

Dengue → vector-borne

HIV → particular body fluids

Poliovirus → mainly fecal-oral

Rabies → infected animal saliva, usually through bites

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Common Mistake: Infection Always Means Symptoms

Viral infections can be:

asymptomatic.

A person can be infected without feeling ill.

Depending on the virus, that person may still be capable of transmission.

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Common Mistake: Vaccination Guarantees No Infection

Vaccines differ in how effectively they prevent:

• infection
• symptoms
• severe disease
• transmission

Protection is not necessarily absolute.

However, vaccines can substantially reduce disease risk and complications for many viral infections.

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Check Your Understanding

1. Define a viral disease.

2. What is a virus?

3. Name the two main components found in all viruses.

4. What additional structure surrounds some viruses?

5. Why can't viruses reproduce independently?

6. Describe the main stages of viral replication.

7. What happens during viral attachment?

8. How can viruses damage host cells?

9. Give five examples of viral diseases.

10. Explain one major difference between viruses and bacteria.

11. How do bacteria reproduce?

12. How do viruses reproduce?

13. Why do antibiotics not treat viral infections?

14. What virus causes influenza?

15. How does influenza mainly spread?

16. Give three common influenza symptoms.

17. What virus causes COVID-19?

18. What is the main method of preventing measles?

19. What virus causes chickenpox?

20. What can varicella-zoster virus cause later in life?

21. What type of virus causes dengue?

22. What is the vector responsible for most dengue transmission?

23. Distinguish between the dengue pathogen and its vector.

24. What does HIV attack?

25. Explain the difference between HIV and AIDS.

26. Give three routes through which HIV can be transmitted.

27. What is antiretroviral therapy?

28. What organ is primarily affected by hepatitis B?

29. How can rabies commonly be transmitted?

30. What is an incubation period?

31. What is an asymptomatic infection?

32. What is an infectious period?

33. Give four factors that can influence viral spread through a population.

34. How does vaccination help prevent viral disease?

35. What is an antiviral medicine?

36. Why can developing antiviral medicines be difficult?

37. Compare prevention and treatment of viral disease.

38. Explain why different viral diseases require different prevention strategies.

39. Explain how mutation and natural selection can change viral populations.

40. Compare bacterial and viral infections in terms of structure, reproduction, transmission, prevention, and treatment.

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Key Terms

• Virus: Non-cellular infectious agent that requires a host cell to reproduce.
• Viral disease: Disease caused by infection with a virus.
• Host cell: Cell used by a virus for replication.
• Capsid: Protein coat surrounding viral genetic material.
• Viral genome: Viral genetic material consisting of DNA or RNA.
• Envelope: Lipid membrane surrounding some viruses.
• Receptor: Molecule that can allow a virus to recognize and attach to a host cell.
• Viral replication: Process by which new virus particles are produced inside host cells.
• Antiviral: Medicine that interferes with viral replication.
• Antiretroviral therapy: Combination of medicines used to suppress HIV replication.
• Supportive care: Treatment that supports body functions without necessarily directly eliminating the virus.
• Vaccination: Method of preparing the immune system to respond to a pathogen or antigen.
• Immune memory: Ability of the immune system to respond more rapidly after previous exposure to an antigen.
• Vector: Organism that transmits a pathogen between hosts.
• Respiratory transmission: Spread through infectious respiratory particles.
• Incubation period: Time between infection and development of symptoms.
• Infectious period: Period during which an infected host can transmit the virus.
• Asymptomatic infection: Infection without noticeable symptoms.
• Outbreak: Increase in disease cases above expected levels in a particular setting.
• Epidemic: Disease occurrence above expected levels within a population or region.
• Pandemic: Epidemic extending across multiple countries or continents.
• Mutation: Change in genetic material.
• Antiviral resistance: Ability of a virus to reproduce despite an antiviral medicine that would normally inhibit it.

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Key Takeaways

• Viral diseases are caused by viruses.
• Viruses are fundamentally different from bacteria.
• Viruses are not cells and must use host cells to reproduce.
• Viral genetic material can be DNA or RNA.
• A protein capsid surrounds the viral genome.
• Some viruses also have an envelope.
• Viral replication involves attachment, entry, production of viral components, assembly, and release.
• Viruses can damage cells and trigger immune responses that contribute to symptoms.
• Examples of viral diseases include influenza, COVID-19, measles, chickenpox, dengue, HIV infection, hepatitis B, polio, and rabies.
• Different viruses use different transmission routes.
• Viral diseases may spread through respiratory particles, body fluids, contaminated food or water, vectors, or animal bites.
• Some viral infections can be asymptomatic.
• Viruses can sometimes spread before symptoms appear.
• Population spread depends on contact patterns, immunity, vaccination, environment, behavior, and characteristics of the virus.
• Antibiotics do not treat viral infections.
• Some viral diseases can be treated with specific antiviral medicines.
• Many viral illnesses also require supportive care.
• Vaccines prepare the immune system before future exposure.
• Prevention and treatment are different strategies.
• Prevention must match the virus's transmission route.
• Respiratory viruses may be controlled partly through vaccination and reducing respiratory exposure.
• Vector-borne viruses may require vector control.
• Bloodborne and sexually transmitted viruses require strategies that reduce relevant body-fluid exposure.
• Viruses can mutate and evolve through natural selection.
• Antiviral resistance can develop when resistant viral variants are selected.
• Combining appropriate prevention strategies can reduce transmission.
• Understanding the differences between viral and bacterial infections is essential for choosing appropriate prevention and treatment strategies.