Chapter Overview

RNA viruses are responsible for a large number of human infections, and are especially prominent causes of emerging diseases.
RNA viruses may be enveloped or not; most contain single-stranded RNA, but one group has double-stranded.
The influenza viruses are highly variable viruses that cause influenza, an epidemic respiratory disease.
Miscellaneous respiratory infections caused by enveloped RNA viruses are parainfluenza, mumps, measles, and croup.
Zoonotic RNA viruses are spread by animal vectors:

Bunyaviruses (hantaviruses) are spread by rodents and are involved in serious respiratory infections.
Arenaviruses are carried by rodents and can cause hemorrhagic fevers.
The arthropod-borne arboviruses are the agents of yellow and dengue fever.

Lyssavirus (rabies virus) is a fatal brain infection acquired from contact with mammals.
Retroviruses are unusual viruses that can use single-stranded RNA to synthesize double-stranded DNA using a reverse transcriptase enzyme.
One prominent example is the human immunodeficiency virus (HIV), the cause of acquired immunodeficiency syndrome (AIDS), a devastating infection of the white blood cells.

AIDS is spread through sexual intercourse and contact with blood.
The destruction of specific immune function by HIV leads to opportunistic infections, cancers, and metabolic dysfunction.

Picornaviruses are very small nonenveloped RNA viruses that may be spread through close contact and orofecally in food and water.
Examples of picornaviruses are:

enteric viruses, including poliovirus, an infection of the central nervous system that can cause paralysis, and hepatitis A, an acute form of liver infection;
rhinoviruses and coxsackieviruses, which are major agents of the common cold syndrome.

Rotavirus is the only double-stranded RNA virus and a common cause of viral gastroenteritis.
Prions are very unusual infectious proteins transmitted by infectious tissues and secretions. They cause slow, progressive neurological diseases called spongiform encephalopathies (Creutzfeldt-Jakob disease).

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