Chapter 7 Solutions — Human Health and Disease

Water-borne diseases such as typhoid, amoebiasis and ascariasis spread through contaminated water. The following measures help prevent them:

1. Drinking only clean, purified water — boiling water before drinking kills most pathogens.

2. Proper disposal of sewage and excreta to prevent contamination of water sources.

3. Periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks.

4. Treatment of public water supplies (chlorination, filtration) before distribution.

5. Eating clean food, fruits and vegetables — washing produce thoroughly before consumption.

6. Maintaining personal hygiene, especially washing hands before eating and after using the toilet.

7. Observing standard hygienic practices in public catering establishments.

Primary lymphoid organs are those where immature lymphocytes differentiate into antigen-sensitive lymphocytes (i.e., where lymphocytes mature):

— Bone marrow (site of origin and maturation of B-lymphocytes; also origin of all blood cells)

— Thymus (site of maturation of T-lymphocytes; a lobed organ located near the heart and beneath the breastbone)

Secondary lymphoid organs are those where mature lymphocytes migrate to and interact with antigens, proliferating to become effector cells:

— Spleen

— Lymph nodes

— Tonsils

— Peyer's patches of the small intestine

— Appendix

— Mucosa-Associated Lymphoid Tissue (MALT) — located within the lining of major tracts (respiratory, digestive and urogenital tracts); constitutes about 50% of the lymphoid tissue in the human body

HIV (Human Immunodeficiency Virus) is transmitted only through body fluids. The main routes of transmission are:

1. Sexual contact: Unprotected sexual contact with an HIV-infected person. Individuals with multiple sexual partners are at particularly high risk.

2. Blood and blood products: Transfusion of HIV-contaminated blood or blood products. People who require repeated blood transfusions (e.g., haemophilia patients) are at high risk.

3. Sharing infected needles and syringes: Intravenous drug abusers who share needles and syringes are at very high risk of HIV transmission.

4. Mother to child (vertical transmission): An HIV-infected mother can transmit the virus to her child through the placenta during pregnancy.

Important note: HIV/AIDS is NOT spread by mere touch or physical contact; it spreads only through body fluids. HIV-infected persons should not be isolated from family and society.