Epidemiology of Small pox and Chicken pox

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

16. Distribution

18. 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

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