Question

Often it is found that individuals who come in contact with an infected individual do not acquire the disease later. Give two explanations for this observation.

Answer 1

Infection is due to the dominance of the pathogen over the host immune system resulting in suppression of defense system by microbial invasion. This leads to the manifestation of the infection with signs and symptoms of particular disease

But not all the individuals who contacted with the infection or pathogen develops the disease which may be attributed to:

i. The resistance and immune power of the host which will overule the pathogen effects leading to inactivation of the pathogens. Body has three lines of defense namely first line of defense consisting of Skin, mucous membranes and their secretions, normal microbiota of the body, second line of defense comprising of Phagocytes, inflammation, fever and antimicrobial substances of the body, finally 3rd line of defense consisting of T cells, B cells and antibodies. When the immune system of the host is strong enough the pathogens are attenuated by these lines of defenses producing no infection in the body even after exposure to infection

Ex. Human polio virus, Opportunistic flora like Candida, E.coli

The other reason would be sometimes even the pathogens contact the body, the person serves as carrier where the person do not show any signs of infection but can serve as a potential carrier of the infection.

ii. Pathogens need certain concentration to mainfest in the body and produce viable population that can take control of the body. Even though there is exposure, the pathogens should reach this limit to show the signs of disease. Anything less than this concentration, the host do not acquire the infection

Ex. S. aureus, and enterococci

iii. Body has immune memory cells which would read the virulence factors of pathogens and remember them and provides protection upon second exposure to the infection. Individuals who are at this stage do not develop infection even when exposed to pathogen

Ex. Chicken pox virus

iv. Vaccination would also result in same effect and the individual do not acquire the disease

Ex. Tuberculosis, Diphtheria, Measles, Mumps etc