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Epidemiology of Small pox and Chicken pox

Epidemiology of Small pox and Chicken pox. Contents. Epidemiological basis of smallpox eradication. History of smallpox eradication. When was the last case reported in India? When was the world declared free of small pox? When was compulsory vaccination for small pox discontinued?.

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Epidemiology of Small pox and Chicken pox

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  1. Epidemiology of Small pox and Chicken pox

  2. Contents • Epidemiological basis of smallpox eradication

  3. History of smallpox eradication • When was the last case reported in India? • When was the world declared free of small pox? • When was compulsory vaccination for small pox discontinued?

  4. Small pox: Obituary • Acute infectious disease caused by Variola virus • Incubation Period 7-17 days • Prodromal symptoms are severe – sudden onset of fever, headache, backache, vomiting, convulsions • Rash appears on 3rd day, centrifugal in distribution

  5. Clinical presentation • Palms and soles frequently involved, axilla is usually free • Predominant on extensor surfaces & bony prominences • Deep seated, passes through stages of macule, papule, vesicle, pustule and scab with scarring • Blindness

  6. Small pox eradication Epidemiological basis • No known animal reservoir • No long term carrier of the disease • Life long immunity after recovery • Detection of cases simple • Persons with subclinical infection did not transmit the disease • Vaccine highly effective, easily administered, heat stable and confers long term protection • International cooperation

  7. After eradication of Small pox • Two potential sources of pox virus infection of humans still remain • Accidental infection with laboratory associated stocks • Infection with animal pox virus

  8. Chicken pox • Varicella-Zoster virus • World wide in distribution • Occurs in epidemic and endemic forms • More during first six months of year • Chicken pox and Herpes zoster - different host responses to the same etiological agent

  9. Agent factors • Human Alpha Herpes virus 3 (V-Z virus) • Latent infection in sensory ganglion • Source - oropharyngeal secretions, lesions of skin and mucosa • Period of communicability is 1-2 days before rash and 4-5 days after the appearance of the rash • SAR- 90 % among household contacts

  10. Host factors • Age - children <10yrs • Immunity - second attacks are rare, CMI is important in recovery and protection • Attack during pregnancy - risk for foetus as well as neonate • Mode of transmission – Droplet infection, Vertical transmission • Incubation period is 14-16 days (7-21 days)

  11. Clinical features • Pre eruptive - mild or moderate fever, malaise lasting for 24 hrs, 2-3 days in adults • Eruptive - Distribution is centripetal, rapid evolution, superficial, not umblicated, scabbing after 4-7 days of rashes, pleomorphism • Fever - shows exacerbation during each fresh crop

  12. Diagnosis • VZV DNA isolation using PCR • Isolation of VZV in vesicular fluid • Serologic screening of serum for IgG antibodies - HCWs

  13. Complications • Pneumonia • Encephalitis • Reye’s syndrome • Fetal wastage • Birth defects – cutaneous scars, atrophied limbs, microcephaly, LBW, cataract, microphthalmia, chorioretinitis, deafness

  14. Control & prevention • Notification • Isolation for 6 days • Antivirals • VZ Ig within 72 hrs of exposure • Vaccine - live attenuated

  15. Distribution

  16. Complications • Small pox Bronchitis to fatal pneumonia, Blindness, Permanent scarring • Chicken pox Self limiting. In immunocompromised and adults can cause haemorrhages, pneumonia, encephalitis, Reye’s syndrome

  17. Prevention • Small pox Live vaccinia virus • Chicken pox Live attenuated vaccine 2 doses 4-8 weeks apart

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