Viruses Small but deadly!

The Black Death

o Also known as the Black Plague, was a devastating pandemic that first struck Europe in the mid-late-14th century (1347–1351).

o It killed between a third and two-thirds of Europe's population.

“Spanish” Flu Pandemic of 1918

o The Influenza spread across the world, killing more than 25 million in six months.

o Some estimates put the total killed at over twice that number, possibly even 100 million.

o Caused by an unusually severe and deadly strain of the subtype H1N1.

Avian “Bird” and Swine Flu

o Strain H5N1 flu

o Possible pandemic threat if it mutates and is transmitted to humans.

o H1N1 – The new threat

A.I.D.S. Pandemico Aids – has killed

~25 million people worldwide.

o ~5 million new infections each year

o 40 million living with it currently.

o HIV leads to AIDSo In 2005 alone,

AIDS claimed an estimated 2.4–3.3 million lives, of which more than 570,000 were children.

SARSo Severe Acute

Respiratory Syndrome o SARS was first

reported in Asia in February 2003.

o Over the next few months, the illness spread to more than two dozen countries in Asia, North America, South America, and Europe before the SARS global outbreak of 2003 was contained.

o According to the World Health Organization (WHO), a total of 8098 people worldwide became sick with SARS during the 2003 outbreak; 774 of these died.

The Ebola Virus

o Causes Viral hemorrhagic fever

What Is A Virus?o Viruses do not fit in the six-

kingdom system because they do not display most of the characteristics of living cells.

o Viruses can only live as parasites.

o They occupy a position between non-living and living.

Virus Anatomyo Range in size from 20-400 nm (1

nm=10-9m)o Made up of nucleic acid and a

protein covering called a capsid.-Capsid is made up of hundreds

of protein molecules. Capsid accounts for 95% of total virus and gives virus its particular shape.

-Nucleic acid is a single-stranded RNA or double-stranded DNA

Virus Shapes

o Most viruses that infect plant and animal cells are:

-Rod-shaped viruses -Globular-shaped viruseso The largest and most complex viruses

are those that attack and infect bacteria – bacteriophages. (see P. 400)

Virus Specificityo Viruses must enter cells to

carry out life processes.o Not every virus is

considered to be disease-causing.

o Viruses are generally selective, and, in most cases, specific viruses enter only specific host cells.

Virus Specificityo Some animal viruses have a broad host

range Eg.

-Swine flu virus (hogs and humans)

-Rabies o Other animal viruses have a very

narrow host range Eg.

-Human cold virus usually infects only the cells of the upper respiratory tract.

-AIDS virus attaches only to a specific site on the surface of T4 white blood cells.

Reproductive Cycles of VirusesFOUR BASIC STEPS1. Attachment and entrance: Virus

chemically recognizes a host cell and attaches to it. Either the whole virus or only its DNA or RNA material enters the cell’s cytoplasm.

2. Synthesis of protein and nucleic acid units: molecular information contained in the viral DNA or RNA directs the host cell in replicating viral components (nucleic acids, enzymes, capsid proteins, and other viral proteins)

Reproductive Cycles of Viruses

3. Assembly of the units: The viral nucleic acids, enzymes, and proteins are brought together and assembled into new virus particles

4. Release of new virus particles: newly formed virus particles are released from the infected cell and the host cell dies.

Two Cycles – See handouto Depending on the type of

virus, virus reproduction can occur two ways:

1. Lytic Cycle – host cell bursts2. Lysogenic Cycle

See page 402