Chapter 24/25 DNA & RNA Viruses

What do parvoviruses have instead of double-stranded DNA?

ssDNA

All RNA viruses are single-stranded except ___?

dsRNA reoviruses

Variola Virus Diseases

• Small pox

• Viriema

Herpes Simplex Virus 1/2 Skeletal Diseases

1. Oral Herpes

2. Whitlows

3. Keratitis

Herpes Simplex 1/2 Nervous/Urogenital Diseases

1. Encephalitis

2. Genital Herpes

HSV-1 Diseases

• usually lesions on the oropharynx, cold sores, fever blisters

  • Early childhood

Type 1 Herpes Specific Diseases

Herpes labialis - cold sores/blisters

Herpetic gingivostomatitis - inflammation of oral mucosa (young children)

Herpetic keratitis - Ocular herpes, inflammation of eye

HSV 2 Diseases

• lesions on the genitalia, possibly oral

  • Occurs in ages 14-29

  • Can be spread without visible lesions

Type 2 Herpes Infections

Genital herpes - Initially fever and swollen groin, then painful genital vesicles that ulcerate. Recurs with stress, menstruation, or bacterial infection

Herpes (1&2) is potentially fatal in ___?

• Neonate and fetus

  • Contaminated by mother at birth

  • C-section if necessary

Herpes Simplex Diagnosis

• Vesicles and discharge are the main clinical signs

• Scraping the base of a lesion reveals giant cells under microscope

• For severe or widespread cases — culture or direct fluorescent antibody tests confirm HSV

Herpes Simplex Treatment

acyclovir, famciclovir, valacyclovir; topical medications

HSV 1 Vs. HSV 2: Trasmission

HSV1: Close face contact

HSV2: Sexual contact

HSV 1 Vs. HSV 2: Latency

HSV1: Occurs in trigeminal ganglion

HSV2: Occurs in sacral ganglia

HSV 1 Vs. HSV 2: Skin lesions

HSV1: Face, mouth

HSV2: genitalia, thighs, buttocks

HSV 1 Vs. HSV 2: Nerve Interventions

HSV1: 5th Cranial Nerve

HSV2: lumbosacral ganglia

Recurrent Infection Stimulis

fever, UV radiation, stress, mechanical injury

Varicella-Zoster Diseases

Chicken Pox (primary)

Shingles/Zoster (reactivation)

Varicella-Zoster Host

• Only humans

  • Respiratory droplets/contact

Varicella-Zoster Diagnosis

• Cutaneous Manifestations

• Shingles seen from multinucleate giants cells

Hepatitis B Diseases

Jaundice

Hepatitis

Hepatitis DNA vs RNA Viruses

• DNA

  • Hepatitis B

• RNA

  • Hepatitis A (food)

  • Hepatitis C (Blood)

  • Hepatitis E (fecal contaminated food)

  • Hepatitis D (defective RNA)

Hepatitis B Growth

• Enters through skin, mucous membrane, or injection

• Multiplies exclusively in the liver, which continuously seeds blood with viruses

  • 107 virions/mL blood

T/F Hepatitis B is typically asymptomatic

True

Hepatitis B Incubation Time

Average 7 weeks

Hepatitis B Groups at risk

homosexuals, drugs addicts

What does hepatitis B increase risk of?

liver cancer - hepatocellular carcinoma

Adenovirus Diseases

Conjuctivitis

Colds

Where does Adenovirus usually infect?

• Lymph tissue

• Respiratory and intestinal epithelia

• Conjuctiva

Adenovirus Structure

Nonenveloped, dsDNA

Adenovirus treatment

• Inactivated polyvalent vaccine

• Severe cases treated with interferon

Parvovirus B19 Diseases

Erythema infectiosum (fifth disease)

RBC damage

How does Erythema infectiosum manifest?

rash of childhood; children have fever and rash on cheeks

Parovirus Structure

• Nonenveloped, ssDNA

• Small size

What animals can Paroviruses harm?

Causes distemper in cats, enteric disease in dogs, fatal cardiac infection in puppies

What is Adeno-associated virus (AAV)

a defective virus; it cannot replicate in host cell without adenovirus

Viruses are limited to ___?

Particular host or cell type

Acquired Defenses against Viruses

combined action of interferon, antibodies, and cytotoxic T cells; frequently results in lifelong immunity

2 types of persistent infections:

• Chronic infections – virus detectable in tissue samples, multiplying at a slow rate; symptoms mild or absent

• Latent infections – after a lytic cycle, virus enters a dormant phase; generally not detectable; can reactivate and result in recurrent infections

DNA viruses causing human disease:

• Enveloped DNA viruses

• Nonenveloped DNA viruses

• Nonenveloped ssDNA viruses

Poxviruses characteristics?

• eruptive skin pustules (pocks or pox) that leave scars

• Largest, most complex animal virus

Poxviruses Growth & Targets

• Multiply in cytoplasm in factory areas

• Target epidermal cells & Subcutaneous connective tissue

Smallpox characteristics

• Infection associated with fever, malaise, prostration (pain), and a rash

• First disease to be eliminated by vaccination

• Exposure through inhalation or skin contact

2 Types of Smallpox

• Variola major – highly virulent, causes toxemia, shock, and intravascular coagulation

• Variola minor – less virulent

Smallpox Vaccination

• vaccine uses a single drop of vaccinia virus punctured into the skin with a double-pronged needle

• Routine vaccination ended in 1972, reintroduced in 2002

Herpesviruses

show latency and cause recurrent infection; viral DNA forms episome (independent DNA)

Herpesviruses Opportunist in ___?

AIDS patients, geriatrics, cancers, etc.

Herpesviruses Structure

• Large enveloped icosahedral dsDNA

• Replicates within nucleus

How are RNA viruses assigned?

based on envelope, capsid, and nature of RNA genome

Influenza growth steps

• Virus attaches to, and multiplies in cells of the respiratory tract

• Segments of RNA genome enter the nucleus

• Finished viruses assembles and buds off

Influenza Glycoproteins Spikes: H

• Hemagglutinin (H) – 15 subtypes; most important virulence factor; binds to host cells

Influenza Glycoproteins Spikes: N

• Neuraminidase (N) – 9 subtypes – hydrolyzes mucus and assists viral budding and release

Antigenic drift

constant mutation; gradually changes the amino acid composition

Antigenic shift

when influenza viruses from different animal hosts swap RNA segments, creating a new virus strain that humans have no immunity to.

Influenza A characteristics

• Most virulent

• Top 10 causes of death in U.S.

Influenza A Growth

• Binds to ciliated cells of respiratory mucosa

• Causes rapid shedding of cells; inflammation

• Can dispose patents to pneumonia

Influenza A history

• After 2003, strains of influenza A viruses that usually infect birds underwent an antigenic shift and began to infect humans

Enveloped Nonsegmented ssRNA Viruses

Rhabdoviruses

Coronaviruses

Flaviviruses

Filoviruses

Rabies growth

1. Virus enters through a bite →

2. replicates at the wound site →

3. travels up nerve endings to the spinal cord and brain →

4. completes its cycle by replicating in the salivary glands for transmission.

Clinical phases of rabies:

• Prodromal phase – fever, nausea, vomiting, headache, fatigue; some experience burning at wound

• Furious phase – agitation, disorientation, seizures, twitching, hydrophobia

• Dumb phase – paralyzed, disoriented, stuporous

• Progress to coma phase, resulting in death

What is SARS?

Severe Acute Respiratory Syndrome

• Airborne transmission

• 9% of cases fatal

How is cornavirus transferred?

Transmitted through droplet or direct contact

Hepatitis C Cause and Acquisition

• Caused by a flavivirus (HCV)

• Acquired through blood contact – blood transfusions, needle

sharing by drug abusers

What does Hepatitis C damage?

liver, can cause chronic liver disease

• Can also increase risk of cancer

What does Hepatitis C Treatment?

interferon and ribavirin to lessen liver damage; no cure/vaccine

2 Hemorrhagic Fevers

1. Yellow Fever

2. Dengue fever

Yellow fever 2 patterns of transmission

• Urban cycle – humans and mosquitoes, Aedes aegypti

• Sylvan cycle – forest monkeys and mosquitoes; South America

Dengue fever carrier

flavivirus carried by Aedes mosquito; not in U.S.; usually mild infection

Dengue Fever Severe Cases

Dengue hemorrhagic shock syndrome (breakbone fever) – extreme muscle and joint pain

Human immunodeficiency virus (HIV)

• Acquired immunodeficiency syndrome

• Causes AIDS

HIV reverse transcriptase (RT)

• enzyme which makes a double stranded DNA from the single-stranded RNA genome

• Genes permanently integrated into host DNA

Early historical signs of HIV

• Severe pneumonia caused by Pneumocystis jirovecii (ordinarily a harmless fungus)

• A rare vascular cancer called Kaposi sarcoma

HIV Causative Agent

• HIV-1 and HIV-2

• T-cell lymphotropic viruses I and II – leukemia and lymphoma

• HIV can only infect host cells that have the required CD4 marker plus a co-receptor

Who accounts for most of HIV infections?

Men, IV drug abusers

HIV Growth Steps

1. Enters through skin/mucous membranes → infects dendritic cells → spreads

2. Macrophages amplify it throughout the body

3. Attaches to CD4 + co-receptor → fuses with cell → enters

4. Reverse transcriptase converts RNA → DNA → integrates into host chromosome

5. Can go lytic (destroy cell) or stay latent (dormant)

HIV pathology tied to which 2 factors?

1. The level of viruses

2. The level of T cells in the blood

Primary effects of HIV

• Leukopenia - destroys lymphocytes (immunity)

• Forms giant T cells/syncytia → virus spreads cell to cell

• Infected macrophages release virus into CNS → inflammation and toxicity

Secondary effects of HIV

• CD4 lymphocytes destruction – opportunistic infections and malignancies during full-blown AIDS

Hepatitis A strucutre

Cubical picornavirus relatively resistant to heat and acid

Is Hepatitis A a chronic infection?

No, not like B or C

Hepatitis A Fecal-oral Transmission

multiplies in small intestine and enters the blood and is carried to the liver

Hepatitis A Symptoms

Flu-like, jaundice seldom present

Hepatitis A Treatment

• No specific treatment once the symptoms begin

• Vaccination

  • Inactivated and attenuated viral vaccines

  • Pooled immune serum globulin for those entering into endemic areas

Which of the following is not caused by a poxvirus

a. molluscum contagiosum

b. smallpox

c. cowpox

d. chickenpox

d. chickenpox

In general, zoonotic viral diseases are ___ in humans

a. mild and asymptomatic

b. self- limited

c. severe and systemic

d. not contagious

c. severe and systemic

Which virus is used in smallpox vaccination?

a. Variola

b. vaccina

c. cowpox

d. varicella

b. vaccina

Herpes simplex 1 usually causes ___, and herpes simplex 2 usually causes ___.

a. cold sores, genital herpes

b. fever blisters, cold sores

c. canker sores, fever blisters

d. shingles, stomatitis

a. cold sores, genital herpes

Herpetic whitlows are ___ infections of the ___.

a. pox, oral cavity

b. CMV, lymph nodes

c. EBV, skin

d. herpes, fingers

d. herpes, fingers

Neonatal herpes simplex is usually acquired through

a. contaminated mother’s hands

b. other babies in the newborn nursery

c. crossing the placenta

d. an infected birth canal

d. an infected birth canal

is an effective treatment of herpes simplex lesions

a. Amantadine

b. Interferon

c. Acyclovir

d. Cortisone

c. Acyclovir

Which herpesvirus is most commonly associated with a dangerous fetal infection?

a. herpes simplex

b. herpes zoster

c. EBV

d. CMV

d. CMV

Varicella and zoster are caused by

a. the same virus

b. two different strains of VZV

c. herpes simplex and herpes zoster

d. CMV and VZV

a. the same virus

A common sign of hepatitis is

a. liver cancer

b. jaundice

c. anemia

d. bloodshot eyes

b. jaundice

A virus associated with chronic liver infection and cancer is

a. hepatitis C

b. hepatitis B

c. hepatitis A

d. both a and b

d. both a and b

Benign epithelial growth on the skin of fingers are called

a. polyomas

b. verrucas

c. whitlows

d. pox

b. verrucas

Paroviruses are unique because they contain

a. a double-stranded RNA genome

b. reverse transcriptase

c. a single-stranded DNA genome

d. an envelope without spikes

c. a single-stranded DNA genome

Adenoviruses are the agents of

a. hemorrhagic cystitis

b. keratoconjunctivitis

c. common cold

d. all of these

d. all of these

Which of the following viruses can be oncogenic in humans

a. papillomavirus

b. Epstein-Barr virus

c. adenovirus

d. both a and b

d. both a and b

Which of the following viruses causes chronic persistent infections?

a. hepatitis B

b. smallpox

c. parvovirus

d. varicella-zoster virus

a. hepatitis B