DNA Viruses of Medical Importance
HSV
Lecture 23 Introduction
Enveloped DNA Viruses
Poxviruses
Naked DNA Viruses
Adenoviruses
Variola Virus
Molloscum Contagiosum
Herpesviruses
HSV 1 & 2
Varicella-Zoster Virus
Epstein-Barr Virus
Cytomegalovirus
HHV 6 & 7
HHV-8 (Kaposi s sarcoma)
Serotypes 1-7
Serotypes 40-42
Papillomaviruses
HPV
Parvoviruses
Parvovirus B19
Viral Hepatitis
DNA
Hepatitis B Virus (HBV)
RNA
HAV, HCV, HDV, HEV
Viruses & Viral Diseases
A virus is a small, acellular, infectious particle.
A virus is also an obligate intracellular parasite.
Viruses are limited to a particular host or cell type.
Viral infections range from very mild to life-threatening.
Many viruses are strictly human in origin, others require transmission
by zoonotic vectors.
Most DNA and a few RNA viruses can become permanent residents
of the host cell.
- Latent infections
- Chronic infections
- Oncogenic
Several viruses can cross the placenta and cause congenital defects.
Certain viruses are also considered teratogens agents that cause
birth defects or kill the embryo outright.
DNA Viruses
Poxviruses
Largest and most complex animal virus family
Enveloped with a large, brick-shaped appearance
Possess dsDNA and have the largest genome of
all viruses
They multiply in the cytoplasm in well-defined sites
called factory areas (carry own polymerases)
Produce eruptive skin pustules called pocks or
pox, which leave small, depressed scars
(pockmarks) upon healing.
Important members of the Poxvirus family include:
Variola virus
causes Smallpox
Vaccinia virus
used to make Variola vaccine
Cowpox virus
used in Jenner s ork
Monkeypox virus
can infect humans
Variola virus & Smallpox
At one time, smallpox was ranked as one of the
deadliest infectious diseases, leaving no civilization
untouched.
Through the efforts of the World Health
Organization, it became the first disease to be
eliminated by vaccination. The last case of
smallpox was seen in 1977.
Strictly a human pathogen
Transmission was through inhalation or direct skin
contact.
Infection associated with fever, malaise, severe
headache, & a vesicular rash throughout the body
Variola major highly virulent, caused
toxemia, shock, and intravascular coagulation
Variola minor
less virulent
Molluscum Contagiosum
Caused by the Molluscum Contagiosum Virus (MCV)
which forms clusters of benign, pink, waxy, tumorlike growths on skin
Transmitted by direct contact and fomites
In the U.S., it is most common in children 1-10 years
of age and is considered an STD in adults
DNA Viruses
Herpesviruses
Large, enveloped, icosahedral dsDNA virus
Named for the tendency of some herpes infections to produce a rash
that spreads (creeps).
All members show latency and cause recurrent infections.
Infections become more severe with age, cancer chemotherapy,
immunosuppression, etc.
Comprises a large family with 8 known to infect humans:
- HHV 1 & 2: Herpes Simplex Virus 1 & 2 (HSV 1 & 2)
- HHV-3: Varicella-Zoster Virus (VZV)
- HHV-4: Epstein-Barr Virus (EBV)
- HHV-5: Cytomegalovirus (CMV)
- HHV-6 & HHV-7
- HHV-8: Kaposi s Sarcoma-associated Herpes Virus (KSHV)
HSV 1 & 2
Varicella-Zoster Virus (VZV)
Etiological agent of Varicella (commonly known
as Chickenpox) and a recurrent infection called
Herpes Zoster (Shingles).
Extremely communicable and transmitted
mainly via respiratory droplets but also skin
contact.
The virus replicates in the respiratory mucosa
(incubation of 10-20 days) and then travels
through the bloodstream and spreads throughout
the body.
Primary Infection
Chickenpox
- Fever and a vesicular itchy rash
- Virus enters neurons (dorsal root ganglia)
and remains latent
A live, attenuated Varicella vaccine is available.
Varicella-Zoster Virus (VZV)
Secondary infection
Shingles
Reactivation of the virus results in
Herpes Zoster (Shingles) with vesicles
localized to distinctive areas
Reactivation by such stimuli as X-Ray
treatments, immunosuppresive and other
drug therapy, surgery, stress
Very painful and tender
Can cause Chicken Pox in newly
infected individuals
Epstein-Barr Virus (EBV)
Causes the disease known as Infectious Mononucleosis ( the kissing
disease )
Transmission: direct oral contact and contamination with saliva
Infects lymphoid tissue and salivary glands
Very ubiquitous in people. By mid-life, 90-95% of all people have been
infected.
In some people, the entire course of infection and latency is
asymptomatic
In children and young adults
mononucleosis causes sore
throat, high fever, and cervical
lymphadenopathy
Epstein-Barr Virus and Cancer
EBV has been implicated in B rki s
lymphoma, a B-cell cancer that usually
develops in the jaw and grossly swells the
cheek.
The prevalence in Africa may be
associated with chronic coinfections with
other diseases, such as malaria.
EBV also has oncogenic
implications in nasopharyngeal
carcinoma in older Chinese
and African men.
Cytomegalovirus (CMV)
Produces giant cells with nuclear & cytoplasmic inclusions called
o ls e e
Very ubiquitous human pathogen
Transmitted in saliva, respiratory mucus, breast
milk, urine, semen, cervical secretions & feces.
Can cross the placenta and is the most common
cause of congenital infection in the U.S (causing
mental retardation and hearing loss).
CMV is commonly carried in a latent state in
various tissues.
Most infections are asymptomatic but can cause
cytomegalovirus mononucleosis similar to EBV.
Groups that may develop a more virulent form of
the disease include newborns and AIDS patients
who can develop fever, severe diarrhea, hepatitis,
pneumonia, blindness and death.
Human Herpes Virus 6 & 7
The most common herpesvirus, with up to 95%
prevalence in tested human populations.
Transmitted by close contact with saliva and
other secretions and targets T cells.
Etiological agent of Roseola, an acute febrile
disease in babies between 2 and 12 months of
age.
Illness begins with fever followed by a faint rose
pink rash over the neck, trunk, and buttocks. The
disease is self-limited and children recover in 2-4
days.
Adults may get mono-like symptoms,
lymphadenopathy and hepatitis
Linked to Multiple Sclerosis, encephalitis, and
cancer
Kaposi s Sarcoma-associated
Herpes Virus (HHV-8)
An STD that infects B cells
Has been isolated from Kaposi s sarcoma, a common
tumor in AIDS patients.
DNA Viruses
Adenoviruses
Non-enveloped (naked) virus
icosahedral capsid, dsDNA
30 types are associated with human disease
Infect lymphoid tissue, respiratory & intestinal
epithelia and conjunctiva of the eye
2 major serotype groups:
Serotypes 1-7 (Respiratory)
Serotypes 40-42 (Gastroenteritis)
- Spread by respiratory droplets
and ocular secretions
- Spread through fecal-oral route
- Cause colds, pharyngitis, viral
conjunctivitis
- Causes acute watery diarrhea
Papillomaviruses
Non-enveloped, icosahedral capsid, dsDNA
Cause Papillomas (Warts)
epithelial growth
benign squamous
Over 100 different strains of the Human
Papillomavirus (HPV)
Transmissible through direct contact,
contaminated fomites, or autoinoculation
Incubation: 2 weeks to more than a year
Plantar Warts
Common Warts
Periungual Warts
HPV and Genital Warts
Most common STD in the U.S.
In excess of 30 million carriers of 35 types of
HPV associated with genital warts (most
common types are 6, 11, 16, and 18)
HPV 16 and 18 cause an estimated 70% of
cervical cancer and most HPV-caused anal,
vulval, vaginal and penile cancer.
Treatment of Warts:
- Most common warts regress over time
- Physical removal via topical medication,
cauterization, freezing, or laser surgery
Two effective subunit HPV vaccines are
available Cervarix (16, 18) and
Gardasil 9
Parvoviruses
Very small, non-enveloped, icosahedral virus
The only single stranded DNA virus
Cause distemper in cats, enteric disease in
dogs, fatal cardiac infection in puppies
Parvovirus B19 causes infection in human
- Disease is called erythema infectiosum or
Fifth Disease
- Common childhood infection spread by
respiratory droplets
- Infection may go unnoticed, though the child
may have a low-grade fever, a characteristic
Slapped Cheek Rash , along ith bod rash.
- Severe fatal anemia can result if pregnant
woman transmits virus to fetus (hydrops fetalis)
DNA Viruses
Viral Hepatitis
Hepatitis an inflammatory disease of liver cells that may
result from several viruses
Interferes ith liver s e cretion of bile pigments such as
bilirubin into the intestines. Bilirubin accumulates in blood &
tissues causing jaundice, a yellowing of the skin and eyes.
Caused by several unrelated viruses
Hepatitis Viruses
Now Includes Hepatitis D (HDV) and Hepatitis E (HEV)
Major Hepatitis Viruses
HAV
HBV
HCV
HDV
HEV
Nucleic Acid
RNA
DNA
RNA
RNA
RNA
Naked or
Enveloped
Naked
Enveloped
Enveloped
Enveloped
Naked
Transmission
FecalOral
Bodily
Fluids
Bodily
Fluids
Bodily
Fluids
FecalOral
Symptoms
Fever,
Diarrhea
Fever,
Rash,
Arthritis
Fever,
Rash,
Arthritis
Infectious
only with
HBV
Fever,
Diarrhea
Chronicity
No
Yes
Yes
Yes
No
Vaccine
Yes
Yes
No
No
No
Hepatitis B Virus (HBV)
Enveloped, icosahedral, dsDNA
Tropism for Liver
A minute amount of blood can transmit infection
and also spread through sex, semen, saliva, IV
drug use, childbirth and breast-feeding
Can become a chronic infection
Increases risk of cirrhosis and hepatocellular
carcinoma