Viruses are infectious agents that can cause disease in humans, animals and plants. They range from those that cause minor illnesses like the common cold to more serious diseases like HIV/AIDS. Viruses insert their genetic material into host cells and use the cell's machinery to replicate. They are host specific and thought to have originated from host cell genetic material. While some viruses can be beneficial for controlling pests, viruses overall are responsible for a wide range of diseases through disrupting normal host functioning. Prevention through vaccines is crucial given viruses cannot be treated with antibiotics.

1. Viral diseases

2. Diseases Caused by Viruses
viruses are
everywhere in
nature, but only a
few cause disease

3. Pathogens
Disease
Causing
agents

4. Also important…
Any agent (not just viruses) that
causes disease is a pathogen.
When a virus inserts its genetic
material into a host’s DNA, it is
called a provirus.
Some viruses replicate very slowly
and only cause damage when
the conditions are “right”. (cold
sores)

5. Viruses are host cell specific.
Most viruses are restricted to
certain kinds of cells (those that
infect plants cannot infect animal
cells).
Why?
Scientists think that viruses
originated from escaped genetic
material from host cells.

6. Viruses can be beneficial…
Bacteriophages – attack & destroy bacteria
Baculovirus – ebola-like virus that attacks
insects
– Could use for pest control in crops
• Cabbage loopers eat
cabbage crops
• Virus can kill pests in days
– (it’s really gross)
… and then there are those that are not so good….

7. RNA or DNA?
Viruses with RNA
– Human immunodeficiency virus
(HIV)
– Influenza viruses
– Rabies
Viruses with DNA
– Warts
– Chickenpox
– mononucleosis

8. Retroviruses
• Contain RNA instead of
DNA
• Copy their RNA into DNA
instead of DNA to RNA
• Examples: AIDS, some
cancers

10. Viral Disease in Humans
• Like bacteria, viruses produce
disease by disrupting the body’s
normal equilibrium
• Unlike bacterial diseases, viruses
can’t be treated with antibiotics
• The best way to protect against most
viral diseases lies in prevention by
the use of vaccines

11. Viral Disease in Animals
• Viruses produce serious
animal disease as well
• Ex.) Foot-and-mouth
disease, Rous sarcoma

12. Viral Disease in Plants
• Many viruses infect plants
• Ex.) Tobacco mosaic virus,
potato yellow dwarf virus

13. Viruses are responsible for a number of
plant diseases
• Approximately 2,000 kinds of plant diseases
have been attributed to viruses
– Plant viruses are responsible for the loss
of over 15 billion dollars annually by
reducing the yield of important
agricultural and horticultural crops
• Once a plant is infected the virus spreads
slowly throughout the plant
• In some instances, plants have been
purposefully infected with a virus in order to
produce traits considered desirable by
gardeners
• Example: Some variegation in leaves
and flowers can be brought about by
viruses 16-13

15. A virus is responsible for the variegation and streaking in
Rembrandt tulips

16. Viroids and Prions
• Scientists have
discovered two virus-like
particles that also cause
disease

17. Viroids
• Single stranded RNA
molecules that have no
surrounding capsid
• Cause disease in plants

19. Prions
• Proteins that cause
disease in animals
Ex.) Mad cow disease

21. Surgical masks provide protection against
the transmission of SARS
16-21

22. Exterminating possibly infected chickens may protect
against bird flu
16-22

23. A provirus is a DNA virus that has been inserted into a
host cell chromosome.

24. Human Immunodeficiency Virus
(HIV)
Acquired Immuno Deficiency
Syndrome (AIDS)

25. How Is HIV Spread?
• Sexual contact
• Sharing contaminated
needles
• Blood transfusions
• Breast feeding (mother to
baby)
• Mother to baby during
pregnancy or birth

26. • HIV is a retrovirus injecting the enzyme, reverse
transcriptase into the cell to copy viral RNA into
DNA.

27. Viruses are host specific – a protein on the surface of the
virus has a shape that matches a molecule in the plasma
membrane of its host, allowing the virus to lock onto the
host cell.

28. • HIV doesn’t target just any cell, it goes right for the cells
that want to kill it. “Helper" T cells are HIV's primary target.
These cells help direct the immune system's response to
various pathogens.

29. HIV undermines the body's ability to
protect against disease by depleting T
cells thus destroying the immune
system.
After many years ofinfect 10 battle, the body has
The virus can a constant billion cells a
insufficient only 1.8 billion to mount an immune
day, yet numbers of T-Cells can be replaced
response against infections. At the point when the
daily.
body is unable to fight off infections, a person is said
to have the disease AIDS.
It is not the virus or the disease that ultimately kills a
person; it is the inability to fight off something as
minor as the common cold.

30. Think about it…
• In the US, there is better than a 1/1000 chance
of contracting HIV during unprotected sex
• A person can be contagious for more than 10
years before any sign of the disease is apparent
• HIV becomes AIDS when the number of immune
cells drops below a predetermined number
• No one dies from HIV or AIDS; people die from
secondary infections (ranging from the common
cold to cancer)
• More than 3 million people (size of Chicago) die
each year
• There are approx. 14,000 new cases of
HIV worldwide every day

31. The Story of Dengue
Virus

32. Dengue Virus
• Single-stranded RNA virus
• Causes dengue hemorrhagic fever
• Transmitted by mosquitoes (Aedes aegypti)
• Serotypes (DEN-1, 2, 3, 4)

33. Dengue Virus
Nature Structural Biology 10, 907 - 912 (2003)

34. Where?
World distribution of dengue viruses and their mosquito vector, Aedes aegypti, (2005)

35. Hepatitis virus

36. Viral Hepatitis - Overview
Type of Hepatitis
A B C D E
Source of feces blood/ blood/ blood/ feces
virus blood-derivedblood-derived blood-derived
body fluids body fluids body fluids
Route of fecal-oral percutaneouspercutaneous percutaneous fecal-oral
transmission permucosal permucosal permucosal
Chronic no yes yes yes no
infection
Prevention pre/post- pre/post- blood donor pre/post- ensure safe
exposure exposure screening; exposure drinking
immunization immunization risk behavior immunization; water
modification risk behavior
modification

37. Hepatitis B virus

38. Introduction
• approximately 350
million people are
infected globally with
HBV.

39. High-risk groups for HBV infection
• People from endemic regions
• Babies of mothers with chronic HBV
• Intravenous drug abusers
• People with multiple sex partners
• Hemophiliacs and other patients requiting
blood and blood product treatments
• Health care personnel who have contact
with blood
• Residents and staff members of
institutions for the mentally retarded

40. Treatment
• Interferon-alpha may be effective
for treating a chronic HBV
infection.
• Hepatitis B immune globulin may
be administered within a week of
exposure and to newborn infants
of HBsAg-positive mothers.

41. Hepatitis C Virus

42. Introduction
• The major cause of parenterally
transmitted non A non B
hepatitis. It eluded identification
for many years. In 1989, the
genome was cloned from the
serum of an infected
chimpanzee.

43. Transmission
• Blood transfusions, blood products
• organ donation
• Intravenous drug abusers
• community acquired: mechanism
unclear. ?
• Vertical transmission ?
• sexual intercourse

44. Chronic Hepatitis C
Factors Promoting Progression or
Severity
• Increased alcohol intake
• Age > 40 years at time of infection
• HIV co-infection
• ?Other
– Male gender
– Other co-infections (e.g., HBV)

45. Treatment, Prevention,and Control
• Recombinant interferon-alpha is
the only known effective
treatment for HCV.
• Illicit drug abuse and transfusion
are the most identifiable sources
of HCV viruses.

46. Mumps, Measles, Influenza, and
Poliomyelitis

47. Chickenpox
- Varicella
Blister-like rash on surface of
skin and mucous
membranes. Blisters
usually appear first on
trunk and face, then
spread to almost
everywhere else.

48. Kaposi’s Sarcoma
Purplish lesions of a skin
cancer not usually seen in
young men Herpes virus

49. Rabies
virus

51. Prevention and treatment