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Anatomy of a Virus - PDF


Next Monday, watch video, on line: Bird Flu: How Safe Are We? Go to: Click on “Are We Safe” Questions will be placed on a link at the video title on syllabus.


Lecture 15

Viruses Are Very Small

Anatomy of a Virus
Viruses composed of two parts: Capsid: Outer protein layer. Genetic material either: RNA DNA

relative size of a virus, bacterium & animal cell relative size of a virus, bacterium & animal cell

Different Kinds of Viruses

Which Kingdom for Viruses?
Plantae Fungi Animalia Protista Monera

all have outer capsid & genetic material inside all have outer capsid & genetic material inside

are viruses alive? are viruses alive?

Lecture 35


Why Aren’t Viruses Alive?
Viruses don’t have characteristics of living organisms:
Not cellular. Cannot reproduce itself. Don’t grow. No metabolism.

What Do Viruses Do?
Viruses invade living cells:
Take over “machinery” of host cell. Host cell reproduces virus. Acts like intracellular parasite.

Scientists don’t consider them alive.

Viral Invasion of Cell
DNA DNA viral DNA viral DNA host cell host cell capsid capsid viral DNA viral DNA incorporated incorporated into host into host DNA DNA
new viral DNA new viral DNA new capsids new capsids

viruses cause many human diseases viruses cause many human diseases

Human Viruses

capsids & capsids & DNA DNA reassembled reassembled

Flu Warts Cold sores Some diarrhea Measles Mumps Polio

Yellow fever Some colds Pneumonia Some cancers AIDS Herpes Lots more

Other Viruses
Viruses cause diseases in other organisms: Plant viruses Bacteriophage = bacterial viruses All organism have viruses. Often host specific.


literally “bacteria eater” literally “bacteria eater”

Lecture 35


Plant Virus
Tobacco Mosaic Virus

Viruses & Diseases
Most don’t cause diseases. Disease causing viruses poorly adapted. Disease viruses are typically the result of recent interactions between two or more species: Birds & humans e.g. bird flu Monkeys & humans e.g. AIDS.

SARS Virus
1 stranded RNA 1 stranded RNA Coronavirus Coronavirus

SARS (Severe Acute Respiratory Syndrome)

Structure of proteinase

SARS (Severe Acute Respiratory Syndrome)
Easily transmitted to inanimate objects. Early 2003 ca 6,000 cases reported & ca 400 deaths Did not become the pandemic anticipated.

Herpes Virus

Herpes virus Herpes virus

Lecture 35


Herpes Symptoms

Not life threatening: cold sores & blisters. More than 500,000 infected/yr. Symptoms may go away but virus always present. Symptoms reoccur especially in time of stress.

Herpes lesions: found on shaft of penis, vagina, vulva, cervix & anus

AIDS Virus

Medical Difficulties
General problems with viruses: Latency period can be many yrs e.g. AIDS. Infection can be permanent e.g. Herpes. Antibiotics have no effect, thus can be hard to treat.

Acquired Immune Deficiency Syndrome (AIDS): Caused by lentivirus: symptoms may not show for many years. Genetic material: RNA. Damages immune system. No known cure for disease.

Human Immunodeficiency Virus (HIV) is the cause of AIDS.

More than 40 million people carry the virus. anti-viral agents not effective.

Lecture 35


AIDS Statistics
One person is infected every 15 seconds. 40% AIDS cases are women. 10% are babies born with AIDS. Most studied virus in history.

History of AIDS
Rapid rise of AIDS in mid to late 1970s. Spread to five continents by 1980. 100,00-300,00 infected Slow awareness of AIDS in 1980s. Many rare diseases & opportunistic infections occurred. Fear of contagion

History of AIDS
Generalizations of infected individuals (4-H’s) in 1981: Homosexuals Haitians Hemophiliacs Hookers Abusers of IV drugs Officially dubbed AIDS.

History of AIDS
Virus first isolated in France in 1983 but largely ignored. AIDS spread still unknown then. Believed casual contact could cause infection. Discrimination against AIDS victims.

History of AIDS
France’s discovery of virus finally “rediscovered” in U.S. in 1984. ca 8,000 AIDS cases & ca 4,000 deaths by end of 1984. First blood test for AIDS available in 1985. Transmission of AIDS finally understood.

History of AIDS
First needle exchange program in Amsterdam Rock Hudson dies of AIDS in 1985, Arthur Ashe in 1993

Lecture 35


Sudden Spread of AIDS
International Travel: Gaetan Dugas (flight attendant) Blood transfusions & Factor VIII. Reusable syringes Polio vaccine?

By End of 1999
Originated in Africa from Simian Immunodeficiency Virus (SIV). Virus in chimpanzees. How did it pass from chimpanzee to man? Hunter theory: drank blood or ate raw meat from monkey.

Different Strains
Two Strains of HIV HIV-1: most common & deadliest strain HIV-2: found in W Africa & less severe strain

HIV Attacks
T-4 lymphocytes: vital to immune system. Cell surface receptors. Mucous membrane & immune cells.

HIV Infection
Average time from HIV infection to development of AIDS is 9-10 yrs. Virus makes 1-10 billion copies of itself each day. Average survival time after developing AIDS is 9 months. With drugs survival time is more than 5 yrs.

HIV Structure
cylindrical core cylindrical core (usually spherical) (usually spherical) thick envelope thick envelope

cell surface receptor cell surface receptor

Lecture 35


HIV Virus Invasion of White Blood Cell

Sites of Infection
Not blood Lymph system destroyed T-4 cells
Cervical lymph nodes Right lymphatic duct Thymus Thoracic duct Cistema chyli Palatine tonsils Axillary Lymph nodes Spleen MucosaAssociated Lymphatic tissue (MALT)(in small intestine

Inguinal Lymph nodes

Lymptatic vessels

Red bone marrow

HIV Infections
Immune system successfully attacks HIV. Some cells remained infected & HIV dormant. Slowly damage immune system. Death from opportunistic malignancy or infection.

HIV Transmission
Sexual contact accounts for most HIV infections (vaginal, anal or oral). Exposure to infected body fluids (intravenous drug users, hemophiliacs). Mother-to-child transmission during pregnancy & child birth.

HIV & AIDS Worldwide

men men

children children women

New HIV Infections in 2005
30 000 – 40 000 180 000 – 280 000
North Africa & Middle East Western Europe Eastern Europe & Central Asia

women 70% HIV positive people live in Africa & 15% in Asia Deaths 2005: ca 3 million (600,000 children under 15). 8,500/day Since 1981 25 million deaths. Problem: rapid spread in population.
(updated 2004)

36 000 – 54 000 45 000 – 80 000

North America

43 000 – 67 000

South & South-East Asia

150 000 – 270 000

East Asia & Pacific

120 000 – 180 000

Latin America

Sub-Saharan Africa

610 000 – 1.1 million
Australia & New Zealand

3.0 – 3.4 million

700 – 1 000

2005 HIV infections: 6,000 people age 15-24 per day


total: 4 - 6 million

Lecture 35


2005 AIDS Statistics
More than 40 million people world wide have AIDS. 20 million women. 3 million children. 3 million died.

2010 Projections:
Most seriously affected countries:
Ethiopia 20% of adult population Nigeria Russia – 8 million China – 10 to 15 million India – 25 million

What happens when a country denies it has a problem?

Treating HIV with Drugs
In 2002 in U.S. 25% of people with AIDS are unaware they have it. Drugs can’t prevent AIDS infection. Drugs for treatment target: Capsid Virus enzymes

HIV Treatment
Drug “cocktail” (multiple drugs) Very expensive & has side effects Virus mutates rapidly making vaccines difficult to make Best current solution: Best current solution: avoid risky behavior. avoid risky behavior.

Influenza (Flu)
Respiratory infection. Symptoms: Fever, coughing and muscle aches. Last a few days. Incubation 1 to 3 days (rapid spread). Fatal complication: viral or bacterial pneumonia.

Flu Pandemics (20th. Century)
Spanish Flu (H1N1), 1918: Deaths: 20-50 million world wide. Twice death toll of WWI. Asian Flu (H2N2)*, 1957-58. Hong Kong Flu (H3N3)*, 1968-69.
*Human flu virus + Avian flu virus transmission pathogenicity

Lecture 35


Swine Flu 1976
Virus similar to Spanish Flu of 1918. National immunization campaign. Attempted to immunize US population, but only achieved 25%. Pandemic did not materialize. Media sensationalize event. Highly politicized.

Wild birds catch the flu. H5N1 avian (“bird”) flu passes to humans. In 2004, 100 million chickens/poultry killed. In June 2004 renewed outbreaks in Indonesia, Malaysia, Vietnam & Thailand. In 2006 spread in Indonesia. H = 16 types N = 9 subtypes Chicken → Human Are we prepared?

Avian Flu

Historical Summary of Bird Flu
1997 (H5N1)………………First bird flu 1999 (H9N2)………………First report in humans 2002 (H7N2)……………….New human strain 2003(H5N1, H7N7, H7N2).New strains appear 2005 (H5N1)……………….Human-human spread 2006 (H5N1)………………Reported in China, USSR, Egypt, Iraq and Africa 200? (H5N1)…………………..Reported in US?

In which Kingdom do we classify viruses? Viruses are composed of _____ & _____. _____ are viruses that attack bacteria. HIV infection attacks the ______.

Which of the following is true of viruses outside the host cell? Which of the following human diseases is not caused by viruses? HIV stands for: The Spanish flu:

Lecture 35


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