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MICROBIOLOGY
WITH DISEASES BY TAXONOMY, THIRD EDITION
Chapter 24
Pathogenic DNA Viruses
Lecture prepared by Mindy Miller-Kittrell, University of Tennessee, Knoxville
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Virus Structure
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DNA Viruses
• Those causing human disease grouped into seven families based on:
– Type of DNA they contain
– dsDNA
– Poxviridae, Herpesviridae, Papillomaviridae,
Polyomaviridae, and Adenoviridae
– ssDNA
– Parvoviridae
– Hepadnaviridae contains dsDNA and ssDNA
– The presence or absence of an envelope
– Size
– The host cells they attack
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Poxviridae
• Double-stranded DNA viruses
• Have complex capsids and envelopes
• Second largest viruses
– Infect many mammals
• Most animal poxviruses are species specific
– Unable to infect humans because cannot attach to human cells
• Infection occurs primarily through the inhalation of viruses
• Close contact is necessary for infection by poxviruses
• Smallpox and molluscum contagiosum the main diseases of humans
• Some diseases of animals can be transmitted to humans
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A poxvirus
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Figure 24.1
The stages of lesions in poxvirus infections
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Figure 24.2
Poxviridae
• Smallpox
– In the genus Orthopoxvirus
– Commonly known as variola
– Exists in two forms
– Variola major
– Variola minor
– The virus moves via the blood to the skin, where it produces pox
– Scars result on the skin, especially on the face
– Smallpox is the first human disease to be eradicated
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Smallpox lesions
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Figure 24.3
Poxviridae
• Smallpox
– Factors that enabled the eradication of smallpox:
– Inexpensive, stable, and effective vaccine
– No animal reservoirs
– Obvious symptoms allow for quick diagnosis and quarantine
– Lack of asymptomatic cases
– Virus is only spread via close contact
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Poxviridae
• Molluscum Contagiosum
– Caused by Molluscipoxvirus
– Spread by contact among infected individuals
– Children
– Sexually active individuals
– AIDS patients
– Skin disease characterized by smooth, waxy papules
– Typically on face, trunk, and external genitalia
– People with normal immunity heal without treatment
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Lesions of molluscum contagiosum
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Figure 24.4
Poxviridae
• Other Poxvirus Infections
– Poxvirus infections also occur in animals
– Transmission to humans requires contact with infected animals
– Infections of humans are usually mild
– Can result in pox and scars but little other damage
– Edward Jenner used cowpox to immunize individuals against
smallpox
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Herpesviridae
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Viruses have enveloped polyhedral capsids and linear dsDNA
Viruses attach to a host cell’s receptor
Viral envelope fuses with the cell membrane to facilitate entry into cell
Most prevalent DNA viruses
Often latent
– Remain inactive inside infected cells
– Reactivation causes recurrence of the disease manifestations
• Assigned species names combining “HHV” and a number indicating
order in which they were discovered
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Herpesviridae
• Infections of Human Herpesviruses 1 and 2
– Often result in slow-spreading skin lesions
– also known as herpes simplex virus or HSV
– Two species
– Human herpesvirus 1 (HHV-1)
– Human herpesvirus 2 (HHV-2)
• - By adulthood, about 80% of Americans have been infected HHV1
Approx. 20% of Americans have HHV-2
Most infections are asymptomatic
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Sites of events in herpesvirus infections
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Figure 24.5
Herpesviridae
• Infections of Human Herpesviruses 1 and 2
– Types of HHV-1 and HHV-2 infections
– Oral herpes
– Genital herpes
– Ocular herpes
– Whitlow
– Neonatal herpes
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Oral herpes lesions
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Figure 24.6
Two manifestations of herpesvirus infections
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Figure 24.8
Herpesviridae
• Infections of Human Herpesviruses 1 and 2
– Epidemiology and pathogenesis of HHV-1 and HHV-2 infections
– Active lesions are the usual source of infection
– Aysmptomatic carriers shed HHV-2 genitally
– Transmission occurs through close bodily contact
– Enter body through cracks or cuts in mucous membranes
– Virus spreads from cell to cell through syncytia formation
– HHV-1 infections typically occur via casual contact in children
– HHV-2 infections occur between ages of 15 and 29 from sexual
activity
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Herpesviridae
• Infections of Human Herpesviruses 1 and 2
– Diagnosis, treatment, and prevention
– Diagnosis
– Characteristic lesions are often diagnostic
– Treatment
– HHV-1 and HHV-2 controlled with chemotherapeutic agents
– Limit duration of the lesions and reduce viral shedding
– Don’t cure the disease or eliminate latent virus
– Prevention
– Health care workers should wear gloves to reduce
exposure
– Sexual abstinence and sex between uninfected partners
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Herpesviridae
• Human Herpesvirus 3 (Varicella-Zoster Virus) Infections
– Causes two diseases
– Varicella
– Often called chicken pox
– Typically occurs in children
– Herpes zoster
– Also called shingles
– Usually occurs in adults
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Herpesviridae
• Human Herpesvirus 3 (Varicella-Zoster Virus) Infections
– Epidemiology and pathogenesis of VZV infections
– Chicken pox is highly infectious disease
– Virus enters skin through the respiratory tract or eyes
– Virus travels via the blood from infection site throughout body
– Characteristic skin lesions appear 2–3 weeks after infection
– The disease is usually mild in children
– Chicken pox in adults is typically more severe
– Latent virus can reactivate producing a rash known as shingles
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Characteristic chicken pox lesions
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Figure 24.9
Latency and reactivation of varicella-zoster virus
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Figure 24.10
Shingles
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Figure 24.11
Dermatomes
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Figure 24.12
Herpesviridae
• Human Herpesvirus 3 (Varicella-Zoster Virus) Infections
– Diagnosis, treatment, and prevention
– Diagnosis
– Chicken pox is diagnosed from the characteristic lesions
– Shingles lesions can be more difficult to diagnose
– Treatment
– Chicken pox is usually self-limiting
– Shingles treatment involves management of symptoms
– Prevention
– Difficult because virus is shed before obvious signs
appear
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Herpesviridae
• Human Herpesvirus 4 (Epstein-Barr Virus) Infections
– Also referred to as EBV
– Can cause a number of different diseases
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Diseases associated with Epstein-Barr virus
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Figure 24.13
Herpesviridae
• Human Herpesvirus 4 (Epstein-Barr Virus) Infections
– Epidemiology and pathogenesis of HHV-4 infections
– Transmission usually occurs via saliva
– Initially infect epithelium of pharynx and parotid salivary glands
– Virus enters the bloodstream and invades B lymphocytes
– Become latent and suppress apoptosis of B cells
– Immune response causes infectious mononucleosis symptoms
– Cytotoxic T cells kill virus-infected B lymphocytes
– Cancer development appears to depend on various cofactors
– Extreme diseases arise in individuals with T cell deficiency
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Herpesviridae
• Human Herpesvirus 4 (Epstein-Barr Virus) Infections
– Diagnosis, treatment, and prevention
– Diagnosis
– Some diseases diagnosed by their characteristic signs
– Treatment
– Burkitt’s lymphoma responds well to chemotherapy
– Mono patients are treated to relieve the symptoms
– Other conditions have no effective treatment
– Prevention
– Hard because virus is widespread and transmitted by saliva
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Herpesviridae
• Human Herpesvirus 5 (Cytomegalovirus) Infections
– Infected cells become enlarged
– One of the more common infections of humans
– Transmission occurs through bodily secretions
– Requires close contact and a large exchange of secretion
– Usually occurs via sexual intercourse
– Also transmitted by in utero exposure, vaginal birth, blood
transfusions, and organ transplants
– Most CMV infections are asymptomatic
– Complications in fetuses, newborns, and immunodeficient patients
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Herpesviridae
• Human Herpesvirus 5 (Cytomegalovirus) Infections
– Diagnosis, treatment, and prevention of HHV-5 infections
– Diagnosis
– Detection of enlarged cells and cellular inclusions
– Treatment
– Treatment of fetuses and newborns is difficult
– Damage usually occurs before infection is discovered
– Fomiversen is used to treat CMV eye infections
– Prevention
– Abstinence and safe sex can reduce chance of infection
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An owl’s eye cell diagnostic for cytomegalovirus infection
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Figure 24.14
Papillomaviridae and Polyomaviridae
• Papillomavirus Infections
– Cause papillomas, commonly known as warts
– Benign growths of the epithelium of skin or mucous membranes
– Papillomas form on many body surfaces
– Often painful and unsightly
– Genital warts associated with an increased risk of cancer
– Transmitted via direct contact and via fomites
– Autoinoculation spreads from one location to another on a person
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The various kinds of warts
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Figure 24.17
Papillomaviridae and Polyomaviridae
• Papillomavirus Infections
– Diagnosis usually based on observation of the papillomas
– Diagnose cancers by inspecting genitalia and by a PAP smear
– Some warts can be removed through various methods
– Prevention of most types of warts is difficult
– Genital warts prevented by abstinence or mutual monogamy
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Papillomaviridae and Polyomaviridae
• Polyomavirus Infections
– Capable of causing tumors in animals and humans
– Can cause other diseases
– BK and JC viruses are endemic worldwide
– Infection outcome depends on the individual’s immune system
– Normal immune systems tend to prevent latent infections
– Compromised immune systems allow latent infections to
become established in the kidneys
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Papillomaviridae and Polyomaviridae
• Polyomavirus Infections
– Reactivation events are different between the BK and JC viruses
– BK virus
– Potentially severe urinary tract infections can develop
– JC virus
– Can cause progressive multifocal leukoencephalopathy
– Viruses infect and kill the white matter of the CNS
– Paralysis and death eventually result
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Adenoviridae
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Contain single, linear dsDNA genome
One of many causative agents of the common cold
Spread via respiratory droplets
Respiratory infections
– Viruses taken into cells lining the respiratory tract via endocytosis
– Symptoms include sneezing, sore throat, cough, headache, and
malaise
• Infection of the intestinal tract can produce mild diarrhea
• Infection of the conjunctiva can result in pinkeye
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Adenovirus
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Figure 24.18
Adenoviral conjuntivitis
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Figure 24.19
Hepadnaviridae
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Enveloped DNA viruses
Genome is composed of both single’ and double-stranded DNA
Includes hepatitis B virus (HBV)
HBV replicates through an RNA intermediary
– Unique among DNA viruses
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The genome of hepadnavirus
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Figure 24.20
Hepadnaviridae
• Hepatitis B Infections
– Causes hepatitis
– Inflammation of the liver
– HBV is the only DNA virus that causes hepatitis
– Viral infection can cause severe liver damage
– Various symptoms
– Jaundice, liver enlargement, abdominal distress, and bleeding
into the skin and internal organs
– Coinfection with hepatitis D virus increases risk of permanent liver
damage
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Hepatitis
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Figure 24.21
Hepadnaviridae
• Hepatitis B Infections
– Virions are shed into saliva, semen, and vaginal secretions
– Transmitted when infected body fluids contact breaks in the skin or
mucous membranes
– Virus spread through infected needles, sexual intercourse, and
passage to babies during childbirth
– Many individuals are asymptomatic or have mild symptoms
– HBV has been shown to be associated with liver cancer
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Estimated incidence of acute hepatitis B in the U.S.
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Figure 24.22
Hepadnaviridae
• Hepatitis B Infections
– Body fluids contain three types of virus particles
– Diagnose by detecting presence of viral antigens
– No universally effective treatment
– The best treatment is prevention
– Hepatitis B cases have decreased
– Due to vaccination and safer sexual practices
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Three types of viral particles produced by hepatitis B virus
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Figure 24.23
Parvoviridae
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Only human pathogen with a ssDNA genome
Smallest of the DNA viruses
Causes a number of diseases in animals
B19 virus is the primary parvovirus of humans
Causes erythema infectiosum
– Also called fifth disease
• Infection results in a reddening of the skin
• Sunlight aggravates the condition
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A case of erythema infectiosum
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Figure 24.24