Chapter 24-DNA viruses

Exam 3

Poxviridae

• dsDNA virus- infects many mammals

• Most animal poxviruses are species specific

• Unable to infect humans because it cannot attach to human cells

• Infection occurs primarily through inhalation of viruses

• Smallpox is main disease

Smallpox process

1. Attachment- starts in respiratory system but moves quickly to other tissues.

2. Entry- endocytosis

3. Synthesis- Carries its own DNA polymerase and RNA polymerase. Codes for several anti-immune system proteins that compose the virus itself. NO DRIFT

4. Assembly- self assembly

5. Release: budding. Membranes act as holding place for the surface viral proteins that are also removed and remain in envelope of virus as it is released from cell. It cell eventually lyses, some smallpox are released without envelope.

• Commonly known as variola (variola major and minor)

• Scars result on skin

Smallpox proteins

• Enters through respiratory tract but spreads to other cells via blood as respiratory cells are loosely packed to is has access to bloodstream. Once in cell, “core” proteins released along with DNA. Genes on DNA code for proteins:

1. SPICE (smallpox inhibitor of complement enzymes)

   • These enzymes cleave C4b and C3b so that an effective C5 convertase can not form. Opsonization effects of C3b are inhibited. No C5 convertase= highly reduced MAC complex

2. CKBP-II (chemokine binding protein type II)

   • These proteins bind to interferons and interleukin-1. As a result, our immune systems antiviral proteins and inflammatory proteins are compromised a great deal.

Factors enabling eradication of smallpox

• Inexpensive, stable, effective vaccine- cowpox

• Aided by lack of antigenic drift

• Obvious symptoms allow for quick diagnosis and quarantine.

Herpesviridae

• Viruses have enveloped polyhedral capsids and linear dsDNA.

• Often latent- have good latent phase

  • Remain inactive inside infected cells

  • Reactivation causes recurrence of disease manifestations

Life cycle of Herpesviridae

1. HV’s are highly restricted to humans

2. Each HV prefers different cell types

3. DNA genome enters nucleus for mRNA transcription

4. Viral gene expression occurs in immediate early, early, and late phases

5. Genome replication is by viral polymerase and accessory factors

6. Egress by exocytosis

Types of Herpesviridae

Human herpesviruses 1 and 2. (HHV 1and HHV2):

• Oten result in slow spreading skin lesions

Types of herpesviruses

• Oral herpes

• Genital herpes

• Ocular herpes

• Whitlow

• Neonatal herpes

Human herpesvirus 3

• Varicella zoster virus

• Chicken pox is highly infectious disease.

• Enters skin through respiratory tract or eyes

• Skin lesions appear 2-3 weeks after infection

• Mild in children and harsh in adults

• Latent virus can reactivate producing a rash known as shingles.

Hepadnaviridae

Hepatitis B infections

• Causes hepatitis (inflammation of liver)

• Jaundice, liver enlargement, abdominal distress, bleeding into skin and abdominal organs

Hepadnaviridae process

1. Attachment to hepatocytes via heparin sulfate proteoglycans on host cell

2. Entry and uncoating or capsid degration

3. Repair here is that the double stranded DNA is acted on by our repair enzymes, modified slightly and converted to a “mini-chromosome”. The DNA can sometimes be incorporated into our chromosomes and this can lead to disruption of our genes and occasionally cancer formation.

4. Synthesis and assembly. Virus assembled in ER and Golgi

5. Release via exocytosis.

Hepatitis B infections

• Virions are shed into saliva, semen, and vaginal secretions

• Transmitted when infected body fluids contact breaks in 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

• Best treatment is prevention.