Chapter 24: DNA Viruses

What all do viruses infect?

Every living cell

Are viruses living? Why?

No, there is no kingdom or domain

How are viruses measured?

Determines concentration of viruses in a sample.

Measure infectious particle, plaque assays or total particles using qPCR for nucleic acids, Hemagglutination (HA), and electron microscopy.

What is the capsid made up of?

Protein coats that enclose and protect their nucleic acid.

What macromolecule is a capsid made from?

Capsomers

What is the function of the capsid?

Protect the nucleic acid

What determines the “shape” of a capsid?

The specific arrangement and interactions of its protein subunits.

What is inside the capsid?

Nucleic acid

What are the 5 steps of viral multiplication?

1. Adsorption: Binding of the virus to specific molecules on the host cell.

2. Penetration/Uncoating: Genome enters host cell, viral nucleic acid released from capsid.

3. Replication: Viral nucleic acid is replicated.

4. Synthesis: Viral protein parts are produced

5. Assembly: New viral particles are constructed.

6. Release: Assembled viruses are released by budding (exocytosis) or cell lysis.

What ways are virions released from the cell?

1. Budding: Nucleocapsid pushes through the plasma membrane, nuclear membrane, or endosomal membrane, acquiring a portion of the membrane as its envelope.

2. Cell Lysis: Virus disrupts the host cell membrane and wall, causing the cell to burst and die to release the progeny.

3. Exocytosis: Viral particles are packaged into vesicles within the cell, then move to the plasma membrane and fuse with it to release viruses outside the cell.

4. Extracellular Vesicles (EVs): Unconventional methods like hijacking exosomal pathways or autophagy for release.

Lytic Phase?

Lytic Phase:

1. Attachment: Phage binds to specific receptors on surface of host bacterial cell.

2. Penetration: Phage injects genetic material (DNA or RNA) into host cell leaving its capsid outside.

3. Biosynthesis: Virus hijacks cell’s machinery to degrade host DNA and replicate its own genome, producing viral components (protein).

4. Maturation: New virions (virus particles) assembled from synthesized genetic material and proteins.

5. Lysis (Release): Virus releases enzymes, break down cell wall, causing it to burst and release numerous new viruses to infect other cells.

Lysogeny Phase

1. Attachment: Phage attaches to the bacterial surface

2. Entry: Phage injects its DNA into the host cell cytoplasm.

3. Integration: Viral DNA integrates into host chromosome, becoming a dormant ”prophage” (or provirus).

4. Replication (Latency): Host cell replicates its DNA, along with incorporated prophage, passing it to daughter cells, often many generations without causing harm.

Difference between lytic and lysogenic?

Lysogenic allows the virus to exist dormant within host cells for generations.

What are the 4 combinations of nucleic acids seen in viruses?

1. Double-stranded DNA

2. Single-stranded DNA

3. Double-Stranded RNA

4. Single-stranded RNA

Are viral infections general or specific?

Highly specific, host-specific.

Cell tropism binds to specific receptors.

What are persistent infections?

Infections that can last years or a lifetime.

What are the 2 types of persistent infections?

Chronic - Virus detached in tissue samples, multiplies at a slow rate; symptoms are mild or absent.

Latent - After lytic cycle virus enters dormant phase; not detachable can reactive and result in recurrent infections.

Can viruses create oncogenic cells?

Some persistent viruses are oncogenic

What does “teratogenic” mean?

Viruses that can cross the placenta, causing developmental disturbances and permanent defects. Malformation of embryo.

What do poxviruses produce?

Eruptive skin pustules called pocks or pox, leaves scars.

How large are poxviruses relative to other viruses?

Largest and most complex animal virus.

Why is smallpox not a current problem in the world?

eliminated by vaccines

What is another name for smallpox?

Variola

What is the difference between variola major and minor?

Major: Highly virulent, caused toxemia, shock, and intravascular coagulation.

Minor: Less virulent.

Of the other mammalian poxviruses, which are human susceptible to?

Monkeypox: Skin pocks, fever, swollen lymph nodes.

Cowpox: Rare, usually confined to hands; other cutaneous sites can be involved.

How many herpesviruses are there?

8 human herpes Viruses:

HSV-1: Herpes simplex 1

HSV-2: Herpes simplex 2

VZV: Varicella Zoster Virus

CMV: Cytomegalovirus

EBV: Epstein-Barr virus

HHV-6: Herpesvirus 6 - roseola

HHV-7: Herpesvirus 6 - roseola

HHV-8: Herpesvirus 8

What behavior is common in Herpesviruses?

recurrent outbreaks of fluid-filled vesicles or blisters.

Know what diseases are caused by HHV-6.

1. Roseola Infantum

2. Alzheimer’s

3. Multiple Sclerosis

4. Hodgkin’s lymphoma

5. Oral carcinoma

6. T-Cell leukemias

What does HSV1 cause?

1. Vesicles occur mucocutaneous junction of lips or adjacent skin; itching and tingling prior to vesicle formation; lesion crust over 2-3 days and heals.

2. Oropharynx

3. Cold sores

4. fever blisters

What age group is the virus typically acquired?

Under age 5 years old

What does HSV2 cause?

lesions on the genitalia, possibly oral. 14-29 ages.

How does transmission of HSV occur?

HSV-1: Close contact, usually of face

HSV-2: Sexual or intimate contact

Where does the virus multiply? Where does it move?

Sensory Neurons moves to ganglia.

How does the site of multiplication differ between 1 & 2?

HSV-1: Enters 5th cranial nerve (trigeminal nerve)

HSV-2: Enters lumbosacral spinal nerve trunk ganglia.

What would be considered a stimuli for a recurrent infection?

1. Fever

2. UV radiation

3. Stress

4. Mechanical injury

Where are locations of infection most commonly seen in HSV1?

Mucocutaneous junction of lips or adjacent skin; itching and tingling before vesicle formation; lesion crusts over 2-3 days and heals.

Where are locations of infection most commonly seen in HSV2?

Clusters of sensitive vesicles on genitalia, perineum, and buttocks; urethritis, painful urination, cervicitis, itching; vesicles ulcerate.,

Can you have infections of HSV1&2 in alternative locations?

1. Hands

2. Buttocks

3. Eyes

4. Thighs

What effect does HSV1 or 2 have on a neonates?

• Fatal

• Infection of mouth, skin (30%), eyes, CNS (50-80%)

• Skin lesions

• Seizures

• Organ damage

What is a whitlow?

Localized infection; usually on one finger; extremely painful and itchy.

HHV3 causes?

1. Chickenpox (varicella)

2. Shingles (herpes zoster)

What does Varicella cause?

1. Itchy, blister-like rash

2. High fever

3. Tiredness

4. loss of appetite

5. headache

What are symptoms?

1. Fever

2. Skin lesions

3. raised red bump to itchy fluid-filled vesicles that crust over; occur in cro

What does zoster cause?

Shingles, painful skin rash with fluid-filled blisters that typically lasts 2-4 weeks.

Recurrent zoster infections occur along?

Associated dermatones, more common in older patients

Are shingles painful?

Yes they are tingling at site, painful vesicles erupt.

Are there vaccinations for varicella-zoster?

Yes

What kind of vaccine is the varicella vaccine? Can it cause an infection?

Varivax, may cause mild rash, rare cases “vaccine-strain” infection.

What age group is advised for Zostavax Shingrix?

50 and older

19+ with a weakened immune systems

What is EBV?

Inflammation of liver or spleen

What does EBV cause?

Infectious Mononucleosis “Kissing Disease”

How is EBV acquired?

Direct oral contact with infected person or contaminated saliva.

What complication associated with EBV is seen as gross swelling in the cheek and is associated with coinfections with malaria?

Inflammation of liver or spleen

What complication associated with EBV causes malignancy of epithelial cells?

Nasopharyngeal Carcinoma (NPC)

What effect does CMV have on a fetus?

Most normal/ Enlarged liver or spleen, microencephaly, ocular inflammation

What does HHV 6 or 7 cause?

Roseola Infantum (exanthem subitum), mild childhood illness marked by high fever followed by a rash.

Does HHV-6 or HHV-7 appear on the neck, trunk, or buttocks?

Both symptoms appear on neck, trunk, buttocks

What type of HHV is associated with Kaposi’s sarcoma?

HHV-8

What does HPV stand for? What does it cause?

Human Papilloma Viruses, caused by 100 different strains of HPV.

What types of warts are caused by HPV?

Common or Seed Wart: Mostly on the hands (HPV 2)

Plantar wart: Occur on soles of feet (HPV 1)

Genital warts: Most common STD, occurs on external and internal genitalia; most common vagina and head of penis (HPV 6 & 11)

Which is caused by HPV2? HPV1?

HPV 2: Common or Seed wart

HPV 1: Plantar Wart

Which strains can cause cervical cancer?

HPV 16 & 18

What is a condylomata acuminata?

How are warts removed?

What was the created of the HPV vaccine to prevent in females?

What do parvoviruses infect that can lead to fatal cardiac infections?

What does erythrovirus =b19 cause?

What kind of symptoms presents in children? What does it look like?

What is hepatitis?

What effect can a hep infection have visible on the body and sclera?

Which of the 3 hep viruses care caused by RNA and which are DNA?

Of the hep viruses, which is:

called serum hepatitis?

prevented with Havrax?

caused by contaminated water or food? what kind of food is high risk?

is more likely to cause a chronic infection?

is more likely to cause an acute infection?

Is transmitted by blood transfusions, sex, needles, infected mother?

Which does not have a vaccine?

Chronic infections from hepatitis can have what effect on the liver?