The DNA Viruses
Chapter 24
1
General Features of Viruses
•
•
•
•
•
•
Obligate Intracellular Parasites
Very small (ultramicroscopic)
Non-cellular
Not Alive
Protein Coat (capsid)
Some have envelopes
2
3
Viruses
• obligate intracellular parasites
• infect animals, plants, & other microbes, etc.
- all forms of life have viruses that infect them
• All DNA viruses are double-stranded except for
parvoviruses, which have ssDNA.
• All RNA viruses are single-stranded except for
dsRNA reoviruses.
• Viruses are limited to a particular host or cell type.
(Host Range)
4
Viruses
• Viral infections range from very mild and
self-limiting to life-threatening.
• Many viruses are strictly human in origin,
others are zoonoses, some transmitted by
vectors.
• Most DNA & a few RNA viruses can become
permanent resident of the host cell.
• Several viruses can cross the placenta &
cause developmental problems.
5
6
Poxviruses
• produce eruptive skin pustules called pocks or pox,
that leave scars
• largest & most complex animal viruses
• have the largest genome of all viruses
• dsDNA….enveloped
• examples
– Variola – cause of smallpox
– Vaccinia – closely related virus used in vaccines
– Monkeypox
– Cowpox
7
Smallpox
• first disease to be eliminated by vaccination
• exposure through inhalation or skin contact
• infection associated with fever, malaise,
prostration, & a rash
– Variola major – highly virulent, caused toxemia, shock,
& intravascular coagulation
– Variola minor –less virulent
• routine vaccination ended in US in 1972
• vaccine reintroduced in 2002 (bioterrorism threat)
8
Smallpox
9
Statue of Edward Jenner
Showing Jenner transferring pus
from the hands of someone
infected with cowpox into
Edward Jenner
scratches in skin of a young boy
• COWPOX
• People can catch cowpox by direct contact with an infected animal and
they then go on to develop pustules, on their hands.
• These are quite painful and there is a general feeling of being unwell.
The incubation period is about 1 week and the illness lasts about 4-6
weeks. There is a full recovery.
• It had always been noticed in rural communities that dairy maids who
caught cowpox would never get smallpox- they were immune.
• Jenner rubbed cowpox pus into scratches of a rural farmboy (James
Phipps) who then got cowpox. Jenner challenged with smallpox , but
the boy did not get smallpox
10
Molluscum
contagiosum
•
•
•
•
•
caused by an unclassified poxvirus
in endemic areas it is primarily an infection of children
transmitted by direct contact & fomites
in US, most commonly an STD
AIDS patients suffer an atypical form which attacks
the skin of the face & forms tumorlike growths
• treatment: freezing, electric cautery, chemical agents
11
Herpesviridae
• Large, enveloped, icosahedral (20-sided polyhedron),
dsDNA
• large family of viruses; 8 infect humans
–
–
–
–
–
–
–
–
HSV-1
HSV-2
VZV
CMV
EBV
HHV-6
HHV-7
HHV-8
12
Herpesviruses
13
Herpesviridae
• latency & recurrent infections
• “Herpes is Forever”
• complications of latency & recurrent
infections become more severe with age,
cancer chemotherapy, etc
• Among the most common & serious
opportunists among AIDS patients
14
Herpes Simplex viruses
• HSV-1- lesions on the
oropharynx, cold sores, fever
blisters
– occurs in early childhood
• HSV-2 lesions on the genitalia
– can be spread without visible
lesions
• humans only reservoir
• treatment: acyclovir, famciclovir,
valacyclovir
15
Herpes Simplex Virus-1
Latency in trigeminal nerve
ganglion
16
HSV-1
gingivostomatitis
17
HSV-2
18
Varicella-Zoster Virus (VZV)
•
•
•
•
•
causes chickenpox & shingles
transmitted by respiratory droplets & contact
primary infection – chickenpox – vesicles
virus enters neurons & remains latent
later, reactivation of the virus results in shingles
with vesicles localized to distinctive areas,
dermatomes
• treatment : acyclovir, famciclovir, interferon
• live attenuated vaccine
19
Early
symptoms
are acute
pain and
redness of
dermatome
followed
by rash
Chickenpox
Shingles
20
VZV Latency and Reactivation
VZV Latency and Reactivation
VZV Latency and Reactivation
Cytomegalovirus (CMV)
• produce giant cells
• transmitted in saliva, respiratory
mucus, milk, urine, semen,
cervical secretions & feces
• commonly latent in various
tissues
• most infections are asymptomatic
• Almost all people have been
exposed to CMV by the time
they reach adulthood.
• 3 groups develop a more virulent
form of disease: fetuses,
newborns, immunodeficient
adults
Giant cell
24
CMV
• newborns may exhibit enlarged liver & spleen,
jaundice, capillary bleeding, microcephaly, &
ocular inflammation, may be fatal
– Babies who survive develop neurological
sequelae; hearing, visual disturbances &
mental retardation
• perinatal CMV infection – mostly asymptomatic,
or pneumonitis, & a mononucleosis-like
syndrome
• AIDS patients – CMV mononucleosis,
disseminated CMV, retinitis,
• transplant patients - pneumonitis, hepatitis,
myocarditis, meningoencephalitis
25
Epstein-Barr Virus (EBV)
• infects lymphoid tissue & salivary glands
• transmission – direct oral contact & contamination with
saliva
• by mid-life 90-95% of all people are infected.
• causes mononucleosis – sore throat, high fever,
cervical lymphadenopathy
• Because of great sanitation in U.S. 70% of college-age
Americans have never had the infection…so a very
vulnerable population for mono
• Long incubation period (30-50 day incubation)
• most cases of infection are asymptomatic
• Burkitt’s lymphoma associated with chronic
coinfections with malaria, etc
26
Infectious mononucleosis (EBV)
27
Swollen tonsils and gray-white exudate
Burkitt lymphoma
B-lymphocyte tumor
associated with chronic
EBV infection
28
Diagnosis:
leukocytosis
with large
odd
lymphoctes
29
Human Herpes Virus 6 (HHV-6)
•
•
•
•
•
•
•
•
•
Also known as human T-lymphotropic virus
transmitted by close contact with saliva, other secretions
very common –95% prevalent
causes roseola, an acute febrile disease in babies 2-12
months
begins with fever, followed by a faint rash
usually self-limited
adults may get mono-like symptoms, lymphadenopathy,
hepatitis
over 70% of Multiple Sclerosis patients show signs of
infection (Meaning of this linkage???)
can cause encephalitis, cancer
30
Roseola
31
• HHV-7 is closely related to HHV-6 causes
similar diseases
• Kaposi’s sarcoma-associated virus or HHV8 is linked with common tumor of AIDS
patients, also may be involved in multiple
myeloma
32
Hepadnaviruses
• enveloped DNA viruses
• never been grown in tissue culture
• unusual genome containing both double &
single stranded DNA
• tropism for liver
• Hepatitis B virus causes hepatitis & can be
a factor in liver cancer
33
Unusual genome
Circular, with
part ds DNA and
part ss DNA
34
Viral hepatitis
• hepatitis – an inflammatory disease of liver
cells that may result from several viruses
• interferes with liver’s excretion of bile
pigments, bilirubin accumulates in blood &
tissues causing jaundice, a yellow tinge in
skin & eyes
• caused by 3 principal viruses
35
36
Hepatitis B virus
• multiplies exclusively in the liver, which continuously
seeds blood with viruses
• 107 virions/mL blood (a lot)
• minute amounts of blood can transmit infection
• sexually transmitted
• high incidence among homosexuals & drug addicts
• can become a chronic infection
• increases risk of liver cancer
• chronic infection controlled with interferon
• HBV vaccine –given in 3 doses over 18 months
37
HBV (clinical features)
38
39
Adenoviruses
• nonenveloped, ds DNA
• 30 types associated with human disease
• infect lymphoid tissue, respiratory & intestinal
epithelia & conjunctiva
• oncogenic in animals, not in humans
• spread by respiratory & ocular secretions
• causes colds, pharyngitis, conjunctivitis,
keratoconjunctivitis, acute hemorrhagic cystitis
Adenoviral
pinkeye
– Adenovirus is only one of many viruses that can cause
“the common cold”!
• vaccine available
40
Papovaviruses
This term/grouping of viruses is becoming less often used
• Papillomavirus
• Polyomavirus
• Simian vacuolating virus
• small nonenveloped icosahedra (20-sided
polyhedron) with dsDNA
41
Papillomavirus
• papilloma – benign, squamous epithelial growth,
wart or verruca
• caused by 40 different strains of HPV
• Common warts (seed warts) – on fingers, etc
• plantar warts – on soles of feet
• genital warts – prevalent STD
• transmissible through direct contact or
contaminated fomites, autoinnoculation (self-spread)
• Incubation – 2 weeks – more than a year
42
Papillomavirus
Plantar wart
Common wart
Genital wart
43
Genital warts
• most common STD in US
• over 6 M new cases each year
• 30 M carriers of one of the 5 types of HPV
associated with genital warts
• CDC estimates sexually active people have a 50%
chance of catching HPV during a lifetime
• strong association with cervical & penile cancer
• Vaccine available
44
HPV Vaccine
• For girls and women 9-26 years of age
• Three doses
– Initial
– 2 month booster
– 6 month booster
• For prevention only…not a treatment
Polyomaviruses
• induce tumors
• JC & BK viruses (named after patients from which the viruses were
first isolated)
•
•
•
•
common throughout the world
majority of infections are asymptomatic or mild
not much is known
BK infection in renal transplants causes
complications in urinary function
• Progressive multifocal leukoencephalopathy
(PML) is an uncommon fatal infection by JC
46
Parvoviruses
• nonenveloped icosahedral virus, ssDNA
• very small diameter & genome size
• causes distemper in cats, enteric disease in dogs,
fatal cardiac infection in puppies
• B19 variety causes fifth disease, (erythema infectiosum),
rash of childhood
– Child may have fever & rash on cheeks
– Severe fatal anemia can result if pregnant woman
transmits virus to fetus
47
Parvoviruses
“slapped face” rash of fifth disease.
48