Section 2

Viral Diseases

• Vectors of viral diseases include humans, animals, and insects.

• Viruses cause many human diseases, including the common cold, flu, hepatitis, rabies, chickenpox, certain types of cancer, and AIDS.

• Some viruses contain oncogenes that can cause cancer, while other viruses convert proto-oncogenes to oncogenes.

• The human immunodeficiency virus (HIV) is an RNA virus spread by sexual contact, by contact with infected body fluids, and from mother to fetus. HIV targets macrophages and thus damages the body's immune system in the disease called acquired immunodeficiency syndrome (AIDS).

• Emerging viruses usually infect animals isolated in nature but can jump to humans when contact occurs in the environment.

• Vaccines have helped to greatly reduce certain viral diseases. Control efforts, including killing mosquitoes and other vectors and quarantining ill patients, have helped reduce the spread of certain viral diseases.

• Antibiotics are ineffective against viral diseases. Viral drugs, such as acyclovir, block specific steps in viral replication.

• Viroids are short, circular, single strands of RNA lacking a capsid that infect plant cells.

• Prions are infectious particles containing protein but no nucleic acids. Prions cause mad cow disease and similar

Vocabulary vector (p. 489) protease inhibitor (p. 491) oncogene (p. 491)

proto-oncogene (p. 491) emerging disease (p. 491)

inactivated virus (p. 492) attenuated virus (p. 492)

viroid (p. 494) prion (p. 494)

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