DNA VIRUSES

1. DNA VIRUSES Level 8 LECTURE 9

2. 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

3. 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

4. A poxvirus Figure 24.1

5. 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

6. Smallpox lesions Figure 24.3

7. 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

8. 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

9. Lesions of molluscum contagiosum Figure 24.4

10. 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

11. 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

12. The various kinds of warts Figure 24.17

13. 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

14. Papillomaviridae and Polyomaviridae (canceled) • 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

15. Papillomaviridae and Polyomaviridae • Polyomavirus Infections (canceled) • 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

16. 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

17. Adenoviral conjuntivitis Figure 24.19

18. 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

19. The genome of hepadnavirus Figure 24.20

20. 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

21. 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

22. A case of erythema infectiosum Figure 24.24