This document provides an overview of viruses and viral diseases. It defines viruses as strands of DNA or RNA surrounded by protein that can only replicate inside host cells. Viruses are not considered alive since they lack characteristics of living things, like the ability to reproduce outside a host. The document describes how viruses cause diseases by destroying host cells during replication and release of new virus particles. It also discusses methods to treat and prevent viral diseases, including antiviral drugs and vaccines which trigger antibody production to develop immunity. The document concludes by noting scientists research viruses to develop new disease treatments and explore virus links to cancer.

1. Chapter 7: Bacteria and Viruses
Lesson 3: What are Viruses

2. Outline:
1 • Characteristics of Viruses
2 • Dead or alive?
3 • Viruses and organisms
4 • Replication
5 • Mutation
6 • Viral Disease
7 • Treatment and Preventing Viral Diseases

3. 1. Baby having
chicken pox
2.Man having
mumps
3. Boy having
measles
4. Boy having
polio
Do they sound familiar ?!!

4. Characteristics of Viruses:
You might have received shots to protect you from these
diseases
Also you might have also received a shot to protect you
from influenza
 What do these diseases have in common??

5. Characteristics of Viruses:
 All these diseases are caused by different Viruses

6. Characteristics of Viruses:
 What are viruses?
 A virus is a strand of DNA or RNA surrounded by a layer of protein
 Through which it can infect and replicate in a host cell

7. Characteristics of Viruses:
 A virus don’t have:
1. Cell wall
2. Nucleus
3. Any other organelles
 The smallest viruses are between 20 and 100 times smaller than most bacteria
 Viruses can have different shapes:
a. Crystal
b. Cylinder
c. Sphere
d. Bacteriophage

8. Do you think that viruses are living things?

9. Dead or Alive?
 Are viruses organized?
 Do they respond to a stimuli?
 Do they use energy?
 Do they reproduce?
 Viruses cannot do any of these things….
Scientists do not consider viruses to be alive because they don’t have all the
characteristics of living organisms

10. Dead or Alive?
 Viruses don’t reproduce…. They replicate
Replication: a process through which virus can make copies of it self, but it must rely
on a living organism.

11. Viruses and Organisms:
 Viruses must use organisms to carry on the processes that we usually associate
with a living cell
1. Viruses have no organelles
2. Unable to take nutrients
3. Unable to use energy
4. They cannot replicate by their own…they must be inside a cell to replicate
 The living cell that a virus infects is called a host cell

12. Latent or Active:
When a virus enters a cell, it can be either active or latent:

13. Replication :
 Virus can make copies of itself
 Virus cannot infect every cell
 Virus can attach to a host cell with specific molecules on its cell wall or cell
membrane
1. After a virus
become active
2. It destroys the host
cell
3. Released into the
host organism
4. They infect other
cells

14. Mutations:
 As viruses replicates, their DNA or RNA frequently mutates
 Mutations enable viruses to adjust to changes in their host cells
The molecules on
the outside of the
cell change to
prevent viruses
from attaching to
the cell
As viruses mutate,
they are able to
produce new
ways to attach to
host cells
These changes happen rapidly that it can be difficult to cure
or prevent viral disease before they mutate again

15. Viral disease:
 Viruses can cause many human disease such as chicken pox, influenza, some
forms of pneumonia
 But… viruses also can infect
They can cause disease such as rabies or
parvo
They can also infect plants as well
In some cases causing millions of dollars
of damage of crop

16. Viral diseases:
 Most viruses
1. Attack
2. Destroy specific cells
3. The destruction causes the symptoms of the disease
a) Some viruses
can cause
symptoms
soon after
infection
b) Such as
influenza
a) Other viruses
might not
cause
symptoms right
away
b) They viruses
are called
latent viruses

17. Viral Diseases:
1. Viruses that causes symptoms soon after infection
1.Influenza
viruses cause flu
2. It infect the cells lining
Your respiratory system
3. The viruses
begin to replicate
immediately
4. Symptoms starts to
appear within 2-3
days
Such as: runny nose
and scratchy throat

18. Viral Diseases:
2. Viruses that might not cause symptoms right away
 These viruses continue replicating without damaging the host cell
1.HIV infects white
blood cells
2. Infected cells
can function
normally
3. Infected
person might
not appear sick
4. The cell can become
active and destroy cells
in the immune system

19. Treating and Preventing Viral Diseases:
 Sine viruses are changing…. Viral diseases can be difficult to treat
 Antibiotics works against bacteria
 Antiviral medicines can be used:
1. To treat viral diseases
2. To prevent them
3. These medicines:
a) Prevent the virus from entering the cell
b) Stop the virus from replicating
 Antiviral are specific to each virus
Like bacteria, viruses can change and become resistant to medicines

20. Treating and Preventing Viral Diseases:
 Health officials use many methods to prevent the spread of viral diseases
Limit contact with infected
human or animal
Practice good hygiene

21. Immunity:
 Have you ever had chicken pox disease??
Did you get it more than one time?

22. Immunity:
 Most people who became infected with chicken pox develop an immunity to the
disease
 This is an example of acquired immunity
 When virus infects a body… body begins to make special proteins called
antibodies

23. Immunity:
 What are antibodies?
 An antibody is a protein that can attach to a pathogen and make it useless
Antibodies
 Binds to viruses and other pathogens
 Prevent the pathogen from attaching to the host
cell
 Target the virus and alerts the body to destroy
them
 Can multiply quickly if the same pathogen enters
the body again
Another type of immunity, called the natural immunity,
develops when a mother passes antibiotics on to her
unborn baby

24. Vaccines:
One way to prevent viral diseases is
Vaccination
What is vaccine?
 Is a mixture containing material from one
or more deactivated pathogens such as
virus
 Vaccine triggers the production of
antibodies
 Because vaccine contains deactivated
pathogens, the organism suffers mild
symptoms or none at all
 When vaccinated, you will not get as sick
if exposed to pathogens again

25. Vaccine:
o Vaccination can prevent diseases in
animals
o Pet owners and farmers get annual
rabies vaccination for their animals
o This protect animals from disease
o Humans are then protected from rabies

26. Research with viruses:
 Scientists are researching new ways to treat or prevent viral diseases
 Scientists are also studying a link between viruses and cancer
 Viruses can cause changes in a host’s DNA and RNA that result in forming a
tumors or abnormal growth
 Because viruses can change very quickly, scientists must always be working on
new ways to treat and prevent viral diseases
 We thought that viruses are harmful
 Scientists have also found beneficial uses of viruses
 They can be used to treat genetic disorders and cancer using gene transfer