1. The DNA Viruses
Chapter 24

2. General Features of Viruses
Obligate Intracellular Parasites
Very small (ultramicroscopic)
Non-cellular
Not Alive
Protein Coat (capsid)
Some have envelopes

3. Figure: Figure 09-03
Caption:
Comparison of naked and enveloped virus, two basic types of virus particles.

4. 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)

5. 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.

7. 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

8. 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)

9. Smallpox

10. Statue of Edward Jenner
Showing Jenner transferring pus from the hands of someone infected with cowpox into scratches in skin of a young boy
Edward Jenner
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

11. 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

12. 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

13. Herpesviruses

14. 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

15. 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

16. Herpes Simplex Virus-1
Latency in trigeminal nerve ganglion

17. HSV-1
gingivostomatitis

18. HSV-2

19. 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

20. Early symptoms are acute pain and redness of dermatome followed by rash
Chickenpox
Shingles

21. VZV Latency and Reactivation

22. VZV Latency and Reactivation

23. VZV Latency and Reactivation

24. 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

25. 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

26. 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

27. Infectious mononucleosis (EBV)
Swollen tonsils and gray-white exudate

28. Burkitt lymphoma
B-lymphocyte tumor associated with chronic EBV infection

29. Diagnosis: leukocytosis with large odd lymphoctes

30. 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

31. Roseola

32. HHV-7 is closely related to HHV-6 causes similar diseases
Kaposi’s sarcoma-associated virus or HHV-8 is linked with common tumor of AIDS patients, also may be involved in multiple myeloma

33. 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

34. Unusual genome
Circular, with part ds DNA and part ss DNA

35. 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

37. 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

38. HBV (clinical features)

40. 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
Adenovirus is only one of many viruses that can cause “the common cold”!
vaccine available
Adenoviral pinkeye

41. Papovaviruses This term/grouping of viruses is becoming less often used
Papillomavirus
Polyomavirus
Simian vacuolating virus
small nonenveloped icosahedra (20-sided polyhedron) with dsDNA

42. 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

43. Papillomavirus
Plantar wart
Common wart
Genital wart

44. 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

45. 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

46. 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

47. 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

48. Parvoviruses
“slapped face” rash of fifth disease.