Passive smoking can be equally dangerous because it exposes the persons to the same harmful effect of smoke.

Passive or second hand smoking means being in the same room or place, where some one is smoking and getting exposed to smoke in the surrounding air.

Once inhaled, the smoke can trigger release of mucus in the bronchioles that blocks the airways. This induces coughing. But prolonged exposures can lead to bronchitis emphysema, respiratory tract infections and eventually lung cancer.

Prevention is always better than cures because some diseases cause extensive damage to the body tissues or organs and have a

(i) Negative effect on their capacity to function.

(ii) Permanent or long term debilitating effect.

(iii) Negative mental and psychological effect.

(iv) Financial burden.

Prevention, therefore is easier and effective, than cure of a disease.

Preventive measures to control microbial infection include

(i) Maintenance of personal and public hygiene by

(a) Proper cleanliness standards and practices.

(b) Proper disposal of waste.

(c) Periodic cleaning of water reservoirs, etc.

(ii) Control or elimination of vectors that transmit diseases by

(a) Checking water stagnation and garbage accumulation.

(b) Using disinfectants or biological methods to check their breeding and spread.

(iii) Proper immunisation by vaccination, wherever available to control or completely eradicate infectious diseases.

(b) The virus is called retro virus because it does not follow the central dogma of biology (DNA $\rightarrow$ RNA $\rightarrow$ Proteins).

Its genetic material is RNA that is transcribed to DNA using enzyme reverse transcriptase.

(c) Yes, the infected cell can survive, while viruses are being replicated and released.

Diseases which are easily transmitted from one person to another, are called infectious diseases.

For prevention and control of such diseases, maintenance of personal and public hygiene is necessary, for this purpose, some common preventive measurer should be taken as follows

(i) Education People should be educated about communicable disease to protect themselves from such diseases.

(ii) Isolation The infected person should be kept isolated to minimise the spread of infection.

(iii) Vaccination People should get vaccination on time to avoid infection.

(iv) Sanitation The sanitation should be improved to avoid infection from polluted water, contaminated food, etc.

(v) Eradication of Vectors The breeding places of vectors must be destroyed and adult vectors should be killed by suitable methods.

(vi) Sterilisation The patient's surroundings and articles of use should be completely sterilised to reduce the chances of infection.