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.
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
9.
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
14.
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
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
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
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.
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.
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.
RCSB PDB, 2008 About dengue virus and how it infects humans to cause dengue fever.
RCSB PDB, 2008 Elelctron micrograph showing the structure of dengue virus
RCSB PDB, 2008 Areas in the world that are affected by dengue viral fever are shown in red
3
Measles is a viral infection with an incubation period of 8-14 days. It is uncommon in the first year of life. Starts with running nose, reddened watery eyes, cough and rising temperature. White (Koplik) spots appear on inside of cheeks on 3rd-4th day. A blotchy red rash starts behind ears and spreads to face and body. Measles is a potentially serious illness, which can include high fever, and complications such as eye and middle ear infection, deafness, croup, pneumonia and, more rarely, brain damage. Call the doctor. Keep child cool. Give plenty of drinks, and a prescribed dose of paracetamol to reduce fever. Call doctor again if further symptoms develop. Poliomyelitis and its symptoms: Poliomyelitis (polio) is a highly infectious disease caused by a virus. It invades the nervous system, and can cause total paralysis in a matter of hours. The virus enters the body through the mouth and multiplies in the intestine. Initial symptoms are fever, fatigue, headache, vomiting, stiffness in the neck and pain in the limbs. One in 200 infections leads to irreversible paralysis (usually in the legs). Among those paralysed, 5%–10% die when their breathing muscles become immobilized. Persons at risk of polio: Polio mainly affects children under five years of age. In 1988, the forty-first World Health Assembly, consisting then of delegates from 166 Member States, launched a global initiative to eradicate polio by the end of the year 2000. This followed the certification of the eradication of smallpox in 1980, progress during the 1980s towards elimination of the poliovirus in the Americas, and Rotary International’s commitment to raise funds to protect all children from the disease. Progress: Overall, in the 15 years since the Global Polio Eradication Initiative was launched, the number of cases has fallen by over 99%, from an estimated more than 350 000 cases in 1988 to 1919 reported cases in 2002 (as of 16 April 2003). In the same time period, the number of polio-infected countries was reduced from 125 to 7. In 1994, the World Health Organization (WHO) Region of the Americas (36 countries) was certified polio-free, followed by the WHO Western Pacific Region (37 countries and areas including China) in 2000 and the WHO European Region (51 countries) in June 2002. Widely endemic on five continents in 1988, polio is now found only in parts of Africa and south Asia. Progress from 2001 to 2002 includes a reduction in polio-endemic countries from ten to seven. Over 500 million children were immunized in 93 countries during 266 supplementary immunization activities (SIAs). Globally, polio surveillance improved in 2002, as reflected in an increase in acute flaccid paralysis (AFP) rates from 1.6 in 2001 to 1.9 in 2002, representing even better detection of AFP cases. Despite these achievements, the Polio Eradication Initiative faced an increase in global cases in 2002 over 2001. In 2002, 1919 cases were reported (as of 16 April 2003), compared to 483 in 2001. This increase can be attributed to an epidemic in India, and a further increase in cases in Nigeria.