This document summarizes key epidemiological factors related to smallpox, chickenpox, and measles. For smallpox, it notes factors that enabled its eradication like lack of animal reservoirs, effective vaccination, and distinctive rash allowing easy detection. For chickenpox, it outlines agent, host, environmental transmission factors and clinical features. For measles, it provides global burden, India statistics, epidemiological determinants like transmission via droplets, and prevention through vaccination or immunoglobulin administration.

1. Epidemiology of
Communicable Diseases
Dr Raghuram V

2. Respiratory Infections
Smallpox Eradication- Epidemiological basis
-No known animal reservoir
-No long term carrier of the virus
-Life-long immunity ,after recovery from the disease
-Case detection was easy because of characteristic
rash which occurred in visible parts of the body
-Persons with sub clinical infection did not transmit
the disease.

3. Contd..
Vaccine highly effective, easily
administered ,heat stable and conferred
long-term protection
International co-operation
Accidental infection/infection with other
pox viruses

4. Chickenpox
EPIDEMIOLOGICAL DETERMINANTS
-AGENT FACTORS
-Agent-V-Z Virus (Human Herpes Virus 3)
-Source of infection-case of chickenpox
-Period of communicability-1-2 days before
and 4-5 days after the appearance of the
rash
-SAR-90% among household contacts

5. Host Factors
Age –children <10 years of age
Immunity –one attack gives durable
immunity
- no age is exempt in the absence of
immunity
Pregnancy-risk for foetus and neonate

6. Environmental Factors
Occurs mostly during the first six months of
the year in India
Little evidence of seasonal trend in
temperate climates

7. Transmission
Droplet infection
Droplet nuclei
Contact infection can occur when an
individual with herpes zoster is the index
case
- Incubation period-14-16 days(7-21days)

8. Clinical Features
Pre-eruptive stage
Eruptive stage
-Distribution
-Rapid evolution
-Pleomorphism
-Fever

9. Complications
Haemorrhages
Pneumonia
Encephalitis
Acute Cerebellar Ataxia
Reye’s Syndrome
Foetal Wastage
Birth Defects
Oncogenicity

10. Diagnosis
Essentially clinical
Examination of vesicle fluid under the
electronic microscope
Serology for epidemiological surveys

11. Prevention
Varicella zoster immunoglobulin(VZIG)
Vaccine

12. Measles
History
-Earliest description given by noted Arab
physician Abu Bacr(865-925 AD)
-Panum-classical epidemiological studies on
measles-1846
-Enders and his colleagues isolated the virus -
1954
-Live measles vaccine licensed for use-1963

13. Problem Statement
Global
-30 million cases, 1 million deaths in a year
- Case fatality rate-2-15% in developing countries
as compared to 0.2% in developed countries.
-Control, Outbreak Prevention, Elimination
-WHO’s Measles Elimination Strategy-Catch-
up,Keep-up, Follow-up

14. Contd…
India
-1987-2.45 lakh cases
-Following implementation of UIP no.of cases
reduced to 52,454 with 55 deaths in 2005
-Underreporting of cases

15. EPIDEMIOLOGICAL DETERMINANTS
-AGENT FACTORS
-RNA Paramyxo virus
-Source of infection-case of measles
-Period of communicability-4 days before
and 5 days after the appearance of the rash
-SAR-90% among household contacts

16. Host Factors
Age –6 months-3 years
- Following the use of vaccine now affects
older age groups
- Immunity-one attack confers life-long
immunity
- Nutrition-follows a severe course in
malnourished children

17. Environmental Factors
Can spread in any season
In temperate climates measles is a winter
disease
India- epidemics occur during Jan-April

18. Transmission
Droplet infection
Droplet nuclei
Incubation period-10 days from exposure
to onset of fever, 14 days to appearance of
rash

19. Clinical Features
Prodromal stage
-Fever,coryza,nasal discharge, redness of eyes
-Vomiting or diarrhoea
- Koplik’s spots-small bluish white spots on a
red base smaller than a pin head on the
buccal mucosa opposite first and second
molars

20. Contd..
Eruptive phase
- Dusky red ,macular or maculo-papular rash
which begins behind the ears and spreads
rapidly to face and neck and extends down
- Diagnosis –based on typical rash and
Koplik’s spots
- Specific IgM antibodies can be used for
diagnosis where the disease is uncommon.

21. Contd..
Post –measles stage
-Failure to recover
-Gradual deterioration into chronic illness
-Increased susceptibility to other bacterial and viral
infections
-Growth retardation
-Diarrhoea
-Reactivation of pulmonary tuberculosis

22. Prevention
1.Measles vaccination –tissue culture vaccine
Age
Administration
Reactions
Immunity
Contacts
Contraindications

23. Contd..
Adverse effects
Combined vaccine
2.Immunoglobulin-0.25ml per kg body
weight given within 3-4 days of exposure
followed by live measles vaccine 8-12
weeks later.