Page 261 - Review of Medical Microbiology and Immunology ( PDFDrive )

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mebooksfree.com mebooksfree.com DNA VIRUSES ssDNA animal species are infected by papillomaviruses, but those mebooksfree.com
• Herpesvirus mebooksfree.com
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PART III Basic Virology
250
viruses are species-specific and do not infect humans.
dsDNA
Adenoviruses

Naked
Naked
Enveloped
with double-stranded linear DNA. They cause pharyngitis,
• Adenovirus
upper and lower respiratory tract disease, and a variety of
• Papillomavirus
other less common infections. There are at least 40 anti-
• Poxvirus*
• Polyomavirus • Hepadnavirus* • Parvovirus These are naked icosahedral viruses (75 nm in diameter)
genic types, some of which cause sarcomas in animals but
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*Viruses labeled with asterisk
Red = icosahedral symmetry
no tumors in humans.
have a polymerase in the virion
(Poxvirus has complex symmetry)
FIGURE 31–1
Classification scheme for DNA viruses.
anemia patients and erythema infectiosum (fifth disease,
These are double-shelled viruses (42 nm in diameter) with
slapped cheeks syndrome)—an innocuous childhood dis-
an icosahedral capsid covered by an envelope. The DNA is
ease characterized by an erythematous “slapped-cheeks”
a double-stranded circle that is unusual because the com-
rash.
plete strand is not a covalently closed circle and the other
strand is missing approximately 25% of its length. Hepatitis
Polyomaviruses
These are naked icosahedral viruses (45 nm in diameter)
with double-stranded circular supercoiled DNA. Two B virus is the human pathogen in this family.
Herpesviruses
human polyomaviruses are JC virus, isolated from patients
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These are enveloped viruses (100 nm in diameter) with an
with progressive multifocal leukoencephalopathy, and BK
icosahedral nucleocapsid and double-stranded linear DNA.
virus, isolated from the urine of immunosuppressed kidney
transplant patients. Polyomavirus and simian vacuolating
tant human pathogens are herpes simplex virus types 1 and
virus 40 (SV40 virus) are polyomaviruses of mice and mon-
2, varicella-zoster virus, cytomegalovirus, and Epstein–Barr
keys, respectively, which induce malignant tumors in a
virus (the cause of infectious mononucleosis).
variety of species.
Poxviruses
Papillomaviruses
Papillomaviruses are naked icosahedral viruses (55 nm in
diameter) with double-stranded supercoiled DNA. The
envelope with an unusual appearance, and a complex cap-
sid symmetry. They are named for the skin lesions, or
human pathogen in the family is human papillomavirus
(HPV). It causes papillomas (warts) of many body sites, These are the largest viruses, with a bricklike shape, an
“pocks,” that they cause. Smallpox virus and molluscum
and certain strains cause carcinoma of the cervix. Many
contagiosum virus are the two important members.
mebooksfree.com mebooksfree.com • Calicivirus mebooksfree.com • Arenavirus* mebooksfree.com mebooksfree.com mebooksfree.com
RNA VIRUSES
dsRNA
ssRNA
(–)
(+)
(+/–)
Enveloped
Naked
Naked
Enveloped
• Hepevirus • Coronavirus • Bunyavirus* • Reovirus*
• Flavivirus
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• Retrovirus*
• Picornavirus
• Filovirus*
• Togavirus
• Orthomyxovirus*
• Paramyxovirus*
• Rhabdovirus*
* Viruses labeled with asterisk
(All others have helical symmetry)
have a polymerase in the virion
FIGURE 31–2
Classification scheme for RNA viruses.
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