Chapters 18 (pp. 334-46)

Viruses - What are they?


Nucleic acid (double or single stranded DNA or RNA)

Protein coat (capsid)

Viral envelope

Help virus attack host


Virus Reproduction

Generalized (cd: Activity)

Can only infect cells in its host range

Protein coat recognition (lock and key fit)

Insert nucleic acid in cell

Reprogram cell to produce virus particles

Emerge from cell

Phage reproduction (virus of bacteria)

Lytic cycle (cd: Activity)

Lysogenic cycle (cd: Activity)


Types of viruses

Bacterial virus

Plant virus

Animal virus


Transmission in Plants

Horizontal Transmission




Vertical Transmission




West Nile Encephalitis

Inflammation of the brain

Commonly found in Africa, E. Europe, W. Asia, Middle East

New to W. Hemisphere in 1999

83 cases reported in 1999, 2000 - all in New York City metro area

9 deaths in 1999, 2000

2001- first cases outside NYC area



Will you contract West Nile virus?



Human Immunodeficiency Virus (HIV)




Reproductive cycle of HIV (cd: Activity)




What about Bird Flu (Avian Influenza)?


Avian Influenza


Does Bird Flu Spread Easily to Humans?



Countries with human cases

East Asia and Pacific (Cambodia, China Indonesia, Thailand Vietnam)

Europe and Eurasia (Turkey)

Near East (Iraq)

Why the Concern?!

Potential for pandemic

Conditions for start of pandemic:



Viral Changes Enhancing Human-Human Transmission


“Adaptive Mutation”


Emerging viruses

Not really “new,” result from:

Mutations of existing viruses

Spread from one host type to another (expanded host range)

Hanta virus: mouse - human from dust/feces

Dissemination of virus from isolated populations to others:

Habitat destruction

World travel, etc.

CDC - Centers for Disease Control

In Atlanta, clearinghouse for disease info.


That's It For Viruses!!!!