1. Natural Resistance Immunology and microbiology 2011

2. Natural and acquired resistance to a specific disease The immunity may be natural or acquired. Acquired immunity may be passive or active.

3. Types Natural Immunity Species immunity. Racial Basis of Immunity Individual resistance. Nutritional status. Differences Due to Age:

4. Natural Immunity not acquired through previous contact with the infectious agent (or with a relative species) largely genetically determined. Little is known about the mechanism responsible for this form of resistance.

5. Species immunity A given pathogenic organism is often capable of producing disease in one animal species but not in another. Basic physiological characteristics of a species, such as its normal body temperature can determine weather or not a microorganism can be pathogenic. Examples: Mycobacterium laprae can produce disease in human but not in monkeys or apes. B. anthrax infects human but not chickens (perhaps because of the higher body temperature of fowl); gonococci infects humans and not chimpanze.

6. Racial Basis of Immunity Within animal species, there may be marked racial and genetic differences in the susceptibility. Some dark skinned human races have a 10 times greater chances of developing disseminated coccidio mycosis following primary infection than the light skinned races.

7. Individual resistance resistance to infection varies with different individuals of the same species and race. Individual having genetic defect in a. immunologic responsiveness b.antibody production c.phagocytic function make them unusually susceptible to infections.

8. Nutritional status protein deficiency may enhance susceptibility. microorganism may be pathogenic by competing for iron with the host. exposure to ionizing radiation or immunosuppressive drugs, and hormonal imbalance all greatly influence individual susceptibility.

9. Differences Due to Age: In general, the very young and elderly are susceptible to bacterial disease than in other age group. Age is important young individuals are susceptible to “children’s diseases” Ex. measles and chicken pox prior to the acquisition of immunity. Conversely, the aged are susceptible to diseases such as pneumonia, presumably as a result of a decline on immune functions with age.

10. Certain individuals have genetic defect which result in selective or general immuno-deficiencies which greatly increases the susceptibility to disease. Other factors : i.include nutrition and personal hygiene. ii. nature of the workplace and its hazards iii. the opportunity for contacts with infected individuals iv. the individual’s hormonal and endocrine balance all affect the selectivity and frequency of certain diseases.