These men start with what appears to be flu-like symptoms, and when brought to the Hospital they very rapidly develop the most vicious type of pneumonia that has ever been seen. Two hours after admission they have the mahogany spots over the cheek bones, and a few hours later you can begin to see the cyanosis extending from their ears and spreading all over the face. It is only a matter of a few hours then until death comes, and it is simply a struggle for air until they suffocate. It is horrible. (Roy as cited in Quinn, 2008, p.128–129).

Source: http://www.pbs.org/wgbh/americanexperience/films/influenza/

Why is it so difficult to develop a vaccine for influenza and HIV?Why have we been able to eradicate some viruses (like polio) but not others?

Viruses

Viruses are pathogens that attack cells from the inside.  They hijack your own DNA and use it against you.  A virus cannot be treated with antibiotics, it can only run its course until your immune system kicks it out.

The influenza pandemic of 1918-1919 killed more people than World War I, at somewhere between 20 and 40 million people.

More people died of influenza in a single year than in four-years of the Black Death (1347).

Known as "Spanish Flu" or "La Grippe" the influenza of 1918-1919 was a global disaster.

Properties of viruses● no membranes, cytoplasm, ribosomes, or other cell

components● they cannot move or grow●they can only reproduce inside a host cell●they consist of 2 major parts - a protein coat, and hereditary

material (DNA or RNA)●they are extremely tiny, only visible with electron microscopes

Structure of DNA (review)

Shape of a DOUBLE HELIX

Each side held together by weak HYDROGEN BONDS

Repeating units of NUCLEOTIDES

Sides of "ladder" are deoxyribose and phosphates

Center is A, T, G, C

A -> TG -> C         *base pair rule

nucleotide

Virus Structure

This is a bacteriophage, a type of virus that attacks bacteria. It is recognizable because it looks like the lunar landing spaceship.

See animation http://www.youtube.com/watch?v=41aqxcxsX2w&feature=related

Virus Structure

Virus has a covering that has a capsid and sometimes an envelope

Inner core contains a nucleic acid molecule (DNA or RNA) and various proteins

Viruses are usually very specific to their host and to the cells they can infect.

Viral Reproduction 

Lytic cycle = reproduction occurs, cells burst

Lysogenic cycle = reproduction does not immediately occur (dormancy) 

1. Attachment (See McGraw Hill animation)2. Penetration - the virus is engulfed by the cell                    (Cell can enter Lysogenic or Lytic Cycle)3. Biosynthesis - viral components are made                        (protein coat, capsid, DNA/RNA)4. Maturation - assembly of viral components5. Release - viruses leave host cell to infect new cells                     (often destroys host)

Viruses cannot reproduce on their own, and must infect a host cell in order to create more viruses.

Lytic vs Lysogenic Pathways of viruses

Starring the phage named Lambda

See: http://highered.mcgraw-hill.com/sites/007352543x/student_view0/chapter20/lambda_phage_replication_cycle.html

Types of Viruses

Bacteriophages - infect bacteriaRetroviruses - have RNA instead of DNA

Check out this Gallery at Virusworld

More virus images at the end of this presentation!

Viruses may be named according to

● the associated diseases (poliovirus, rabies)● the type of disease caused (murine leukemia virus)● the sites in the body affected or from which the virus was first

isolated (rhinovirus, adenovirus)● where they were first isolated (Ebola virus, Hantavirus),● the animal that carries the virus (bird flu, swine flu)● for the way people imagined they were contracted (dengue = ‘evil

spirit’; influenza = ‘influence’ of bad air).

Focus on Human Immunodeficiency Virus (HIV)

(Link) HIV Animation - how virus infects cells

Video: HIV Life Cycle - drugs that affect reverse transcriptase, integrase, protease, CD4 receptors

See Also: HIV Coloring Assignment

What we know about HIV.....

Developing a vaccine for AIDS is difficult because it is a RETROVIRUS.  RNA mutates easily and each individual virus can be slightly different from the others.  In fact, different viruses can exist within the same person.

See:  HIV coloring

Related to Viruses 

Viroids - even smaller than viruses, consist of RNA strands that lack a protein coat

Prions - "rogue protein", believed to be the cause of Mad Cow Disease, also may cause Kuru in cannibal tribes

See:  http://highered.mcgraw-hill.com/sites/007352543x/student_view0/chapter20/how_prions_arise.html

How Do Vaccines Work?

1.  Once you have gotten a virus, such as chicken pox, your body develops the immunity to that virus.  

2. Vaccines are made by growing a weakened or killed form of the virus (often grown in eggs)

3.  This form of the virus is injected into a person's body, which causes an immune response, and immunity to the virus.

   - Remember Jenner's cowpox vaccine?

RV = rotovirus; DTaP = diptheria, tetanus, pertussis (whooping cough);  Hib = haemophilus influenza type B;  PCV = pneumococcal vaccine; IPV = inactivated polio virus;  MMR = measles, mumps, rubella,  

Some parents are opting out of immunizations due to fears about vaccine safety.  

In response, government agencies are producing commercials to encourage parents to get their child vaccinated.

Discuss:

1.  What are the risks of vaccines?  Are they safe?2.  Would you have your own child vaccinated?3.  Should the government force immunizations?

Anti- Viral Drugs

There are two FDA-approved antiviral drugs recommended by CDC. The brand names for these are Tamiflu® (generic name oseltamivir) and Relenza® (generic name zanamivir).

Tamiflu binds to the active site on neuraminidase which prevents the virus from leaving the cell and infecting other cells

Other antivirals block the viruses at various stages of their life cycle, such as blocking cell receptors, preventing attachment or preventing viral replication after the virus has entered the cell.

Various Images of Viruses for Your Viewing Pleasure

INFLUENZA

BACTERIOPHAGE

H1N1

SMALLPOX