Infectious and Non-infectious Diseases

(i) Infectious Diseases: The diseases which spread due to infection by micro-organisms are called
infectious diseases.
→ It is communicated from diseased person to healthy person, caused by some biological
agents/pathogens like viruses, bacteria, fungi, protozoans, fungi worms.

(ii) Non-infectious Diseases: The disease which does not spread by contact between infected and
healthy person through air and water, is called non-infectious disease.
Example: Arthritis, heart disease.

Different Micro-organisms
SARS Viruses

→ SARS viruses are coming out of the surface of an infected cell (see the arrows for example).
→ 500 nanometer = 0.5 micrometer = 0.001 millimeter.
→ Trypanosoma is a protozoan organism.
→ It causes sleeping sickness.
→ The saucer-shaped substance lying next tothe protozoa, is a red blood cell.
Staphylococcus bacteria
→ The Staphylococcus bacteria causes acne.
→ The scale is indicated at the line at the top left of the picture. It is 5 micrometers long.
Adult roundworm
→ Adult roundworm is found in the small intestine.
→ Its technical name is Ascaris Lumbricoides.
→ The ruler next to it shows 4 centimeter to give an idea of the scale.
→ Leishmania, the protozoan organism causes kala-azar.
→ The organisms are oval-shaped, and each has one long whip-like structure.
→ The immune cell is about ten micrometres in diameter.


→ Antibiotics blocks biochemical pathways important for bacteria. Hence, they are effective against
them. Example: Penicillin, tetracycline.
→ Many bacteria make a cell wall to protect themselves, the antibiotics (Penicillin) blocks the
bacterial process that builds cell wall.
→ Antibiotics works only against the bacteria and not against the viruses.

Means of Spread of Infectious Diseases


→ Infectious diseases spread from an infected person to a healthy person through air, water, food,
vectors, physical contact and sexual contact.
• Through air: By sneezing and coughing, the microbes spread into air and enter into the body of
healthy person, like common cold, tuberculosis, pneumonia etc.
• Through water : The microbes enter into our body by drinking/eating polluted and contaminate
water/food, like cholera, amoebic dysentery etc.
• Vectors: Some organisms like female anopheles mosquito also work as a vector of disease, like
malaria, dengue, yellow fever etc.
• Through sexual contact: Syphilus, AIDS spread by sexual contact with infected person. AIDS virus
can also spread through blood transfusion and from the mother to her child during pregnancy an
through breast feeding.