Iceberg concept of disease occurrence

The presentation describes the Iceberg Concept in Disease Epidemiology, Determinants of it shape-size and uses

1. EPIDEMIOLOGIST 1/10 9/10 Clinician Disease Iceberg Represents Burden of the Disease in a population Latent, subclinical, undiagnosed & carrier states in the community/ population By: Dr. Bhoj R Singh Epidemiology, IVRI, Izatnagar

2. Iceberg concept of disease occurrence Methods to measure Severity & Prevalence of Disease in a population The analogy of an iceberg is used to describe the disease pattern in the community or the population. The study of the "iceberg phenomenon of a disease“ tells of the progress (pathogenesis and spread) of a disease from its sub-clinical stages to apparent disease state. The tip of the iceberg represents what the clinicians see and submerged is the part explored and made visible by the epidemiologists.  The large hidden part of the iceberg is what constitutes the mass of unrecognized disease in the population and determines the fate of any disease control program.

3. Disease free group Diseases like hypertension, diabetes,  anemia,  malnutrition, parasitic infestation, cancers and infectious diseases like Johne’s disease with little known morbidity are presented by large submerged portion of iceberg. Similar is the case with detection and control undiagnosed reservoir of disease and are real challenge to modern technique for elucidation of the iceberg under cover.

4. 1 2 3 4 5 Diagnosed and controlled Diagnosed but not controlled Misdiagnosed cases Population at risk Risk free group

5. Size & shape of Iceberg of a disease depends upon Agent-host-environment relationship Natural history of disease(pathological condition to complete recovery) Virulence Pathogenisity Resisatnce succeptibility Temperature Moisture etc.

6. Factors determining the size of a disease iceberg in a population Agent Factors Virulence, genetic drifts & shifts, adaptability, host range, survivability Environmental factors Indoor environment Outdoor environment Host Factors: Genetic make up Early life events Immunological status (vaccination, innate, acquired) Occupation/ use Companions Other concurrent diseases/ infections etc.

7. Infectious diseases Diseases with vast base - Bovine tuberculosis, Human tuberculosis, Bovine lukemia virus, Mastitis (sub-clinical cases) Jhones disease, prion disease, rabies (long ip ) Rickettsiosis (low specific and sensitive diagnostic tests). Parasitic infestations Diseases with visible tip- 1. Tetanus , Anthrax , Rabies (less sub-clinical cases) 2. Staphylococcal food poisoning, pasteurellosis , influenza (short ip )

8. Non- infectious diseases Mostly metabolic diseases/ disorders. Cardiac problems, Diabetes mellitus, hypothyroidism, hypertension etc. (mostly in dog) , milk fever (in cattle). Production problems. Nutritional deficiency disorders.

9. How to determine in-apparent cases Screening surveys: It is the search for unrecognized disease/sub-clinical disease in a population by means of rapid test. Early detection of disease ( prescriptive screening ) Whole population ( mass screening ) Target population ( strategic screening ) Rapid and reliable test ( high specificity and sensitivity )

10. Giving importance to ill animals only. No clinical signs no disease. Only a single agent is cause of infection. False interpretation of clinical intervention. Dependency on clinical records. Mistakes made by epidemiologist while making an iceberg model

11. Uses For detection of sub-clinical and in-apparent cases Treatment of in-apparent cases Control of diseases with more number of sub-clinical cases To have a detailed knowledge regarding natural history of diseases

12. Uses of Iceberg Concepts in Disease Control Primary Prevention Secondary Prevention Tertiary Prevention Before Occurrence/ entry of disease -Population strategy -High Risk strategy e.g. Tran-boundary measures, Import prohibitions, Vaccination, iradication At incipient stage of disease -Screening case finding, treatment isolation. Less effective, painful e.g. Glanders and Avian Flu, FMD & Brucella vaccination When disease is in outbreak form. Sanitation, education, social measures (movement restrictions.

13. Prevalence Prevalence is defined as number of instances of disease or related attributes in a known population, at a designated time, without distinction between old and new cases Probability of getting infected

14. Types Point prevalence Amount of disease in a population at a particular point of time Cross sectional/snap shot of the disease Number of individuals having a disease at a particular point of time Population at risk at that point in time To study of chronic disease in a population

15. Period prevalence Specified period of time(beginning + number of new cases during that period) Period prevalence = Number of cases that occurred in a given period(old + new) Number of people in the population during this period Longitudinal study Suitable for acute diseases Life time prevalence Number of individuals having diseases at least part of their life

16. Reference Concepts of Epidemiology: An integrated introduction to the ideas, theories, principles and methods of epidemiology by Raj S. Bhopal http://www.vetmed.wsu.edu/courses-jmgay/EpiMod2.htm Veterinary Epidemiology by Michael Thrushfield Veterinary medicine and human health By CW Schwabe https://en.wikipedia.org/wiki/Prevalence

17. Quiz Define iceberg model of disease occurrence. Give ice-berg model for Infertility in cattle, PPR in Goats & Blue Tongue in Sheep. How will you use iceberg model for control of Brucellosis in pigs. Give ice-berg strategy to control FMD. How ice-berg strategy differs from conventional disease control methods? List the important diseases of animals and birds with inverted iceberg model.