Chapter 24: Introduction to Viruses that Infect Humans: The DNA Viruses

Viruses in Human Infections and diseases

smallest parasites with the simplest biological structure

How do viruses infect someone?

DNA or RNA molecules are surrounded by a protein coat; obligate parasites that enter a cell, instruct its genetic and molecular machinery to produce and release new viruses

DNA viruses

• are double-stranded except for parvoviruses, which have ssDNA

• most are budded off the nucleus

RNA viruses

• are single stranded except for dsRNA reoviruses

• most multiply and released from the cytoplasm

Viruses are limited to..

a particular host or cell type

Viral infections

range from asymptomatic to mild to life-threatening

Virus origins

many viruses are strictly human in origin, others are zoonoses transmitted by vectors

Course of viral disease

invasion at portal of entry and primary infection; some viruses replicate locally, others enter the circulation and infect other tissues

Common manifestations of viral infections

rashes, fever, muscle aches, respiratory involvement, swollen lymph nodes

Body defenses to viral infections

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

Lytic cycle

rapid course of many viral infections

2 types of persistent infections

• Chronic infections

• Latent 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

Persistent infections

• long term

• last many years or a lifetime

some persistent viruses

are oncogenic

Teratogenic

developmental disturbances and permanent defects cause by several viruses crossing the placenta

Diagnosis of viral diseases

symptoms, isolation in cell or animal culture, serological tests for antibodies; some tests for antigens

How are animal viruses categorized?

according to nucleic acid (DNA/RNA) , capsid, and presence or absence of envelope

DNA viruses causing human diseases

• Enveloped DNA viruses

• Nonenveloped DNA viruses

• Nonenveloped ssDNA viruses

Enveloped DNA viruses

• poxviruses

Poxviruses

• Larges and most complex animal viruses

• have the largest genome of all viruses

• dsDNA

what do poxviruses produce?

eruptive skin pustules (pocks or pox) that leave scars

where do poxviruses multiply?

in cytoplasm in factory areas

Poxviruses specificity

for cytoplasm of epidermal cells and subcutaneous connective tissues

Smallpox

First disease to be eliminated by vaccination

How can you be exposed to smallpox?

through inhalation or skin contact

smallpox infection

associated with fever, malaise, prostration, and a rash

• Variola major

• Variola minor

Variola major

highly virulent, caused toxemia, shock, and intravascular coagulation

Variola minor

less virulent

Smallpox Vaccination

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

When did the routine vaccination of smallpox end in the U.S?

in 1972

When was the smallpox vaccine reintroduced?

in 2002 for military and medical personnel

Molluscipoxvirus

much more common poxvirus

What skin disease does Molluscipoxvirus cause?

molluscum contagiosum

where is Molluscipoxvirus distributed?

throughout the world, with highest incidence occurring in certain Pacific islands

How is Molluscipoxvirus transmitted?

by direct contact and fomites

Molluscipoxvirus in endemic areas

it is primarily an infection of children

Molluscipoxvirus in the U.S

most commonly an STD

Molluscipoxvirus effects

lesions are small, smooth mascules in genital area and thighs

Molluscipoxvirus in AIDS patients

suffer an atypical form which attacks the skin of the face and forms tumor-like growths

Treatment of poxviruses diseases

freezing, electric cautery, chemical agents

Poxviruses in mammalian groups

• cowpox

• rabbitpox

• mousepox

• elephantpox

What type of poxviruses in mammalian groups are humans susceptible to?

• monkeypox

• cowpox

Monkeypox in humans

skin pocks, fever, swollen lymph nodes

Cowpox in humans

rare, usually confined to hands; other cutaneous sites can be involved

Enveloped DNA Viruses

• Herpesviruses

Herpesviruses

All members show latency and cause recurrent infection; viral DNA forms epistome

Common and serious opportunists among AIDS patients

How does herpesviruses become more severe?

Clinical complications of latency and recurrent infections become more severe with advancing age, cancer chemotherapy, or other conditions that compromise the immune defenses

Herpesviruses structure

large enveloped icosahedral dsDNA

Herpesviruses Classification

• Herpes simplex 1 and 2 (HSV)

• Herpesvirus 3

• Herpesvirus 4

• Herpesvirus 5

• Human herpesvirus 6 and 7

• Herpesvirus 8

Herpes simplex 1 (HSV)

usually lesions on the oropharynx, cold sores, fever blisters

• Occurs in early childhood

Herpes simplex 2 (HSV)

lesions on genitalia, possibly oral

• occurs in ages 14-29

• Can be spread without visible lesions

Herpesvirus 3

varicella-zoster virus (VZV), chickenpox and shingles

Herpesvirus 4

Epstein-Barr virus (EBV), associated with infection of the lymphoid tissue

Herpesvirus 5

cytomegalovirus (CMV), infects the salivary glands and other viscera

Human herpesviruses 6 and 7 (HHVs)

roseola

Herpesvirus 8 (KSHV)

implicated in Kaposi sarcoma

How is Herpes Simplex (HSV) transmitted?

direct exposure to secretions containing the virus; active lesions most significant source; genital herpes can be transmitted in the absence of lesions

how does HSV multiply?

sensory neurons, moves to ganglia

• HSV-1 enters 5th cranial nerve

• HSV-2 enters lumbosacral spinal nerve trunk ganglia

How is recurrent infection of Herpes Simplex triggered?

• by various stimuli - fever, UV radiation, stress, mechanical injury

• Newly formed viruses migrate to body surface, producing a local skin or membrane lesion

Type 1 Herpes Simplex in Children and Adults

• Herpes labialis

• Herpetic keratitis

Herpes labialis (fever blisters or cold sores)

• most common recurrent HSV-1 infection

• Herpetic gingivostomatitis especially in young children

Herpetic gingivostomatitis

Inflammation of the oral mucosa (gums, tongue, soft palate, and lips )

Herpetic keratitis (ocular herpes)

Inflammation of the eye, latent virus travels into the ophthalmic rather than the mandibular branch of trigeminal nerve

• Gritty feeling in the eye, conjunctivitis, sharp pain, and sensitivity to light

Type 2 Herpes infection

• Genital herpes

Genital herpes

herpes genitalia- starts with malaise, anorexia, fever, and bilateral swelling and tenderness in the groin; clusters of sensitive vesicles on the genitalia, perineum, and buttocks; urethritis, painful urination, cervicitis, itching; vesicles ulcerate

Recurrent Genital herpes

Recurrent bouts usually less severe, triggered by menstruation, stress, and concurrent bacterial infection

Herpes of the Newborn

HSV-1 and HSV-2 infections potentially fatal in the neonate and fetus

How are newborns contaminated with herpes?

by mother before or during birth; hand transmission by mother or infant

Herpes infection in newborns

infection of mouth, skin, eyes, CNS

How can you prevent herpes of a newborn?

preventative screening of pregnant woman; delivery by C-section if outbreak at the time of birth

Herpetic whitlow

HSV-1 or HSV-2 can penetrate a break in the skin and cause a localized infection; usually on one finger; extremely painful and itchy

Who are more at greater risk of Herpetic whitlow

Workers in the fields of obstetrics, gynecology, dentistry, and respiratory therapy

HSV-1 encephalitis

rare complication but most common sporadic form of viral encephalitis in the U.S., life-threatening

Who are more prone to severe disseminated herpes HSV-1 encephalitis

Those with underlying immunodeficiency

Diagnosis of Herpes Simplex

• Vesicles and exudate are typical diagnostic symptoms

• Scrapings from base of lesions showing giant cells

• Culture and specific tests for diagnosing severe or disseminated HSV; direct fluorescent antibody test

Treatment of Herpes Simplex

acyclovir, famciclovir, valacyclovir; topical medications

Varicella-Zoster Virus (VZV)

Humans only natural host. Infection transmitted by respiratory droplets and contact

• Varicella (chickenpox)

• Herpes zoster (shingles)

Varicella (chickenpox)

primary infection of Varicella- Zoster Virus (VZV)

How does chickenpox enter the body?

Characteristic vesicles. Virus enters neurons and remains latent

Herpes zoster (shingles)

• reactivation of chickenpox

• more common in older patients

what in the body does shingles affect?

Dermatomes

Diagnosis of Varicella-Zoster Virus (VZV)

Cutaneous manifestations of varicella and shingles are sufficiently characteristic for ready clinical recognition

How can shingles be confirmed?

from multinucleate giant cells in stained smears prepared from vesicle scrapings

How can unequivocal shingles be identified?

with fluorescent antibody detection of viral antigen in skin lesions, DNA typing, or culture

Treatment of Varicella-Zoster Virus (VZV)

• treat symptoms in uncomplicated infections; acyclovir, famciclovir, interferon for systemic disease

• Live attenuated vaccine (Varivax) for chickenpox and shingles

The Cytomegalovirus (CMV) Group

Produce giant cells with nuclear and cytoplasmic inclusions

How is Cytomegalovirus (CMV) group transmitted?

in saliva, respiratory mucus, milk, urine, semen, cervical secretions

Infections of Cytomegalovirus (CMV) Group

• Most infections are asymptomatic

• commonly latent in various tissues

What are the three groups that develop a more virulent form of Cytomegalovirus (CMV) Group disease?

• fetuses

• newborns

• immunodeficient adults

Cytomegalovirus (CMV) Infections in newborns

may exhibit enlarged liver and spleen, jaundice, capillary bleeding, microcephaly, and ocular inflammation; may be fatal

What happens when babies survive CMV infections?

Babies who survive develop neurological sequelae, hearing, visual disturbances and mental retardation

Perinatal CMV infection

mostly asymptomatic, or pneumonitis, and a mononucleosis-like syndrome

AIDS patient CMV infection

CMV mononucleosis, disseminated CMV, retinitis

Epstein-Barr Virus (EBV)

Ubiquitous virus; infects lymphoid tissue and salivary glands

Transmission of Epstein-Barr Virus (EBV)

direct, oral contact and contamination with saliva

Epstein-Barr Virus (EBV) in industrialized countries

college-age population is vulnerable to infectious mononucleosis (mono or kissing disease)

by mid-life, 90-95% of all people are infected

Who is highly susceptible to EBV?

Anyone with an immune deficiency

Disease of EBV

• Infectious mononucleosis