viruses

Viruses

The word virus means “poison” in Latin.

Introduction

Influenza pandemic of 1918 Smallpox in the 18th and 19th century. AIDS statistics…

Viral Diseases

Common Cold Flu (influenza) Mumps Measles Smallpox Chicken Pox Hepatitis Warts

More Viral Diseases…

Cold Sores Polio AIDS Bronchitis Viral Pneumonia Mononucleosis West Nile Virus Rabies

How are viral illnesses treated?

Some have a vaccine to protect you. Rest, plenty of fluids and time… Sometimes an antibiotic is given to

prevent a secondary infection.

Germs are everywhere. How can you avoid being infected?

Wash your hands!!! The 3 most common places to get germs:

#3 Door knob #2 Computer mouse #1 Shopping cart handles http://www.youtube.com/watch?v=MWQ86R-aT-I

http://www.youtube.com/watch?v=RHqNk8_rOHk&feature=related

History of Vaccines

1796 – Edward Jenner (England) Took infected matter from a sore on the

hand of local milkmaid who had cowpox. He rubbed it into small incisions on the

arm of an 8 year old boy named Edward Phipps.

The boy developed a cowpox sore on his arm.

6 weeks later:

Jenner took some infected matter from a victim of smallpox and rubbed it into incisions made in Phipp’s arm again.

The boy remained healthy! Jenner produced a vaccine for

smallpox.

Louis Pasteur - 1884

Produced a weakened infective material from rabid dogs that was used as a rabies vaccine.

First used on a young boy who had been bitten by a rabid dog.

Rabies symptoms

After a symptom-free incubation period that ranges from 10 days to a year or longer (the average is 30 to 50 days), the patient complains of malaise, loss of appetite, fatigue, headache, and fever. Over half of all patients have pain (sometimes itching) or numbness at the site of exposure. They may complain of insomnia or depression.

Two to 10 days later, signs of nervous system damage appear, hyperactivity and hypersensitivity, disorientation, hallucinations, seizures, and paralysis. Death may be sudden, due to cardiac or respiratory arrest, or follow a period of coma that can last for months with the aid of life-support

measures.

Jonas Salk - 1953

Created a polio vaccine. He actually killed the active form of the

virus and used it as a vaccine. 1952 – 57,000 cases of polio. 1957 – virtually no cases.

Albert Sabin - 1960

Treated the polio virus to weaken it. Produced a longer lasting immunity

to polio than the Salk vaccine.

Vaccinations: artificial immunity

1. Inject a dead or weakened form of the virus (called an antigen.)

2. Your body produces antibodies. 3. The antibodies recognize the protein coat

of the virus and hold it as it enters the body. 4. Macrophage (a type of white blood cell)

surround and digest the virus. 5. You are now immune to this virus.

macrophage engulfs antigen by phagocytosis.

Definitions:

Antigen – A substance that stimulates the production of antibodies.

Antibodies – A substance produced by plasma cells (in the blood) in response to specific antigens. They “hold” the antigen until white blood cells (phagocytes) surround and destroy it.

Definitions cont…..

Vaccines – a commercially produced antigen of a particular disease.

It is not as “strong” as the actual disease itself.

Passive immunity – Babies receive antibodies from their mother.

It is temporary: it usually lasts for only 6-12 months.

More definitions…

Pathogen – an agent that causes disease.

Discovery of a Virus - 1933

Read pages 455-456 in textbook.

Size of a virus

Much smaller than any cell. Smallest is 17 nm (.000000017 meter) or

17 billionth of a meter! (nm = 10-9 meter) The largest is 100 nm (.0000001 nm) or

1 ten millionth of a meter. Barely visible in an electron

microscope. http://www.cellsalive.com/howbig.htm

Composition of a Virus

A strand of nucleic acid (DNA or RNA) surrounded by a protein coat known as a capsid.

It may also have an outer “envelope” that it has taken from a host cell.

It is the shape of the capsid or outer envelope that our immune system recognizes.

Is a virus a living organism?

Living things vs. Virus Made of cells Not a cell Metabolism No metabolism Use energy No cell respiration Grow/develop No growth or development

Definite life span Life span? Reproduce Need host cell to reproduce Respond to stimuli “Inert” (inactive)

Bacteriophage - “bacteria eater”

See page 457 in textbook.

Lytic Cycle – 5 steps

Step 1 – Attachment – Virus attaches to a specific receptor site on a cell.

Step 2 – Penetration – Virus enters the host cell Step 3 – Replication – Viral DNA and protein is copied. Step 4 – Assembly - DNA and protein is assembled into a

virus. Step 5 – Release – Viruses rupture the cell membrane and

are released to infect other cells. http://biology.about.com/gi/dynamic/

offsite.htm?site=http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit3/viruses/adlyt.html

Lysogenic Cycle

Same as the lytic cycle but the viral DNA becomes incorporated into the host cell’s DNA.

It lies “dormant” until a later date. http://student.ccbcmd.edu/courses/

bio141/lecguide/unit3/viruses/lysolc.html#si

Viral Subunit Reassortment

Two strains of a virus infect a cell at the same time.

The nucleic acid (DNA or RNA) mix to create new combinations.

New viruses are produced. *It is believed this happens with cold and flu

viruses commonly. http://www.hhmi.org/biointeractive/

animations/subunit/sub_middle_frames.htm

Gene Therapy – A useful purpose of a virus

The harmful DNA is removed from a virus. A “helpful” strand of DNA is inserted in its

place. Allow virus to deliver the genes to their

target cells. http://www.edu365.cat/aulanet/comsoc/

Lab_bio/simulacions/GeneTherapy/GeneTherapy.htm

Problems with gene therapy:

Locating the correct cells. Genes accidentally spliced in the wrong

place. May trigger a nearby oncogene (cancer

causing gene.) May cause too much of something to be

produced. May cause a severe immune response.

Current Research with gene therapy:

What diseases could be treated with gene therapy? (From AMA website.)

About 4,000 diseases have been traced to gene disorders. Current and possible candidates for gene therapy include cancer, AIDS, cystic fibrosis, Parkinson’s and Alzheimer’s diseases, amyotrophic lateral sclerosis (Lou Gehrig's disease), cardiovascular disease and arthritis.