Infectious Disease

Infectious Disease

1. Causes of Disease

   • Health = a state of physical, mental and social well-being, including the absence of disease and infirmity.
   • A pathogen = an organism that can cause disease e.g. bacteria, fungi and viruses.
   • Parasite = an organism that lives in or on another organism and causes damage to the organism e.g. tapeworms, roundworms and fleas.
   • Diseases can also be caused by genetic defects, nutritional deficiencies and environmental factors e.g. toxicity.
   • Infectious disease = diseases that are passed between individuals e.g. malaria, HIV and TB.

2. Malaria

   • Caused by the parasite Plasmodium
     • Plasmodium is a eukaryotic, single-celled parasite.
   • It is transported by mosquitoes, which are vectors (they don't cause the disease but spread the infection by transferring it from one host to another.
     • Mosquitoes transfer the Plasmodium parasite into an animal's blood when they feed on them.
   • Plasmodium infects the liver and RBCs and disrupts the blood supply to the vital organs.

3. AIDS

   • Caused by HIV
     • HIV infects human white blood cells as it can only reproduce inside the cells of the organism it has infected because it cannot reproduce on its own.
       • After the virus has reproduced, it kills the WBC at it leaves.
     • HIV is spread by unprotected sex, infected bodily fluids e.g. blood by sharing needles, and from mother to foetus (through placenta/breast milk/during childbirth)
   • AIDS is a condition where the immune system deteriorates and eventually fails due to the loss of WBCs. The sufferer is more vulnerable to other infections e.g. pneumonia.

4. TB

   • Tuberculosis is a lung disease caused by the bacterium Mycobacterium tuberculosis.
   • It is spread through droplets in the air e.g. when a person sneezes and someone else breathes it in.
   • Many people with TB don't show symptoms but if they become weakened e.g. by malnutrition, then the infection can become active. Then they will show symptoms and pass it on.

5. Global Impact

   • Developing Countries
     • Limited access to good healthcare so people are less likely to be diagnosed and treated.
     • Limited health education so people do not learn about the transmission of diseases.
     • Limited equipment to reduce spread of infections.
     • Overcrowded conditions increases risk of droplet transmission.