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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 Copyright © 2011 Pearson Education Inc. Virus Structure Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. A poxvirus Copyright © 2011 Pearson Education Inc. Figure 24.1 The stages of lesions in poxvirus infections Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. Smallpox lesions Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. Lesions of molluscum contagiosum Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. Herpesviridae • • • • • 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 Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. Sites of events in herpesvirus infections Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. Oral herpes lesions Copyright © 2011 Pearson Education Inc. Figure 24.6 Two manifestations of herpesvirus infections Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. Characteristic chicken pox lesions Copyright © 2011 Pearson Education Inc. Figure 24.9 Latency and reactivation of varicella-zoster virus Copyright © 2011 Pearson Education Inc. Figure 24.10 Shingles Copyright © 2011 Pearson Education Inc. Figure 24.11 Dermatomes Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. Herpesviridae • Human Herpesvirus 4 (Epstein-Barr Virus) Infections – Also referred to as EBV – Can cause a number of different diseases Copyright © 2011 Pearson Education Inc. Diseases associated with Epstein-Barr virus Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. An owl’s eye cell diagnostic for cytomegalovirus infection Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. The various kinds of warts Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. Adenoviridae • • • • 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 Copyright © 2011 Pearson Education Inc. Adenovirus Copyright © 2011 Pearson Education Inc. Figure 24.18 Adenoviral conjuntivitis Copyright © 2011 Pearson Education Inc. Figure 24.19 Hepadnaviridae • • • • 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 Copyright © 2011 Pearson Education Inc. The genome of hepadnavirus Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. Hepatitis Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. Estimated incidence of acute hepatitis B in the U.S. Copyright © 2011 Pearson Education Inc. 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 Copyright © 2011 Pearson Education Inc. Three types of viral particles produced by hepatitis B virus Copyright © 2011 Pearson Education Inc. Figure 24.23 Parvoviridae • • • • • 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 Copyright © 2011 Pearson Education Inc. A case of erythema infectiosum Copyright © 2011 Pearson Education Inc. Figure 24.24