Coupon Accepted Successfully!


DNA Viruses

1. 1.Smallpox, vaccinia and other poxviruses
a. Poxviruses :
Characterized by brick shaped morphology, visible by light microscope
  1. Double stranded DNA genome
  2. Only DNA viruses that replicate in cytoplasm where viral particles accumulate to form eosinophilic inclusions, or Guarnieri bodies, visible by light microscope 

b. Small Pox : Last case reported in 1977 in Somalia

WHO officially declared in 1980 that small pox has been eradicated completely


c. Factors contributing to this accomplishment :

  1. Universal interest in eliminating this costly disease with high mortality and morbidity
  2. Infection's long incubation and low communicability
  3. Ease of diagnosis of skin lesions by histology or antigen detection
  4. Human - sole reservoir of infection
  5. No carrier state
  6. Availability of live virus vaccine: which was resistant to temperature changes & drying
  7. Only known remaining repositories of small pox virus are in research labs in USA & Russia 

d. Variola Virus : Existed in 2 strains      

  1. Variola Major (Small pox) [ Case mortality - 20 -50%]
  2. Variola Minor (Alastrim) [ Milder form of smallpox case mortality less than 1% ] 

e. Smallpox : Transmission requires close contact

  1. IP : 12 days
  2. C/F : Fever, single crop, macular rash - progressing to typical vesicular and pustular lesion over 1 -2weeks 

f. Vaccinia :   Virus used for vaccination against small pox

  1. Probably derived from cowpox, variola virus or hybrid of the two
  2. Now a laboratory virus, no natural host
  3. Per cutaneous administration of vaccinia virus vaccine results in protective cellular and humoral immune response in more than 95% of primary vaccinee
  4. Formation of pustule and scab at the site of inoculation is indicative of immunity
  5. Immunity wanes after 10 - 20yrs; Revaccination after 10yrs - recommended
  6. Routine vaccination for small pox discontinued in 1971
  7. Now recommended for health care employees and lab employees who work directly with vaccinia virus vectors and selected groups exposed to pox viruses (eg Military personnel and individual who work with animals) 

g. Complications :

  1. Generalized vaccinia - in otherwise healthy individual, generally self limited
  2. Eczema vaccinatum - Disseminated cutanoeus lesions in highly susceptible patients with eczema or other chronic skin diseases and is occasionally fatal
  3. Progressive vaccinia (vaccinia necrosum) - severe, potentially fatal illness in individuals with immunodeficiency - acquired / congenital, iatrogenic (glucocorticoid therapy), HIV individuals
  4. Post infectious encephalitis - Rare (3 cases in 1million) - Fatal in 15 - 25% cases with 25% patients with permanent neurological sequelae
  5. Vaccinia can be transmitted to susceptible individuals by vaccinee thus vaccination is C/I in those whose household contacts who have eczema, are immunocompromised or pregnant 

h. Molluscum Contagiosum : Benign disease characterized by

  1. Pearly, flesh coloured umblicated skin lesions 2 - 5mm in diameter
  2. Infection transmitted by close contact including sexual intercourse
  3. Can occur anywhere, but mainly genital region; palms and soles spared
  4. Disease self limited, no systemic complication
  5. Associated with advanced stages of HIV infection. Disease more generalized, severe and persistent in    AIDS patients. Involves face and upper body
  6. Diagnosis: By histological demonstration of cytoplasmic eosinophilic inclusions (molluscum bodies/Henderson Peterson bodies)
  7. The virus has not been cultured so far *Virus identification by electron microscopy & molecular methods

T/t : - No specific systemic treatment

  • Only physical ablation techniques used 

i. Monkey pox viruses :

  1. Infect non human primates
  2. Humans infected if come in direct contact with infected animal
  3. C/F :   * Human disease is rare
  4. Vesicular rash, similar to small pox
  5. Occasionally fatal in children and adults who have not received small pox vaccine 

j. Other pox viruses: Cause localized vesicular lesion when human come in direct contact with infected animal (zoonotic infection)

  1. Cowpox virus
  2. Pseudocow pox virus (Milker's nodule)
  3. Buffalopox   
  4. Bovine papular stomatitis virus
  5. Orf virus (contagious pustular dermatitis)

Test Your Skills Now!
Take a Quiz now
Reviewer Name