Topic outline

    • Communicable Diseases

      You must have noticed that sometimes your mother does not allow you to go out to play or to meet your friends when you are sick. Neither, she allows others to meet you. Do you wonder why?

      This is why because there are some diseases which are infectious and spread when a person comes in contact with sick person. Disease caused by microorganisms when an infected person comes in contact with another person is called communicable disease. Example: influenza, measles, malaria etc.  Communicable diseases are also known as infectious diseases or transmissible diseases.

      Diseases caused due to inadequate intake of an essential nutrient in the diet are called deficiency diseases. These are non-infectious or non-transmissible i.e. these are not passed on from one person to another. Example: scurvy (lack of vitamin C), rickets (lack of vitamin D), and anemia (iron-deficiency).

      Unhealthy habits and behaviors such as smoking, chewing tobacco or drinking alcohol can lead to diseases. Such do not spread from person to person. Example: hypertension, diabetes and cancer etc.


      Non-infectious or non-transmissible diseases are called non communicable diseases. These include deficiency diseases and diseases caused by unhealthy habits.

      Causes of Communicable diseases

      These diseases are caused by different kinds of germs. The chances of a person getting ill depend upon the number of germs entering his body and the body’s immune system i.e. resisting power of the body against the disease causing germs.

      The mere entry of germs into the body does not cause disease. Germs need appropriate conditions such as warmth, moisture, and body’s low resisting power to multiply rapidly.

      Diseases, like influenza, diphtheria, cholera, typhoid, malaria, etc. are communicable diseases. The germs of these diseases are transferred from a sick person to a healthy person by air, water and food or through an insect, like houseflies and mosquitoes or by physical contact with an infected person.


      Vectors or Disease Carriers

      Organisms such as insects, mites, and ticks that transmit germs to human being and animal are called vectors. They spread diseases like malaria, dysentery, cholera, typhoid etc.

      The insects feed on human foodstuffs, wastes and garbage lying in the open or around the drain or dirty water bodies. They sit on these dirty areas from where they pick up and transport various disease agents.


      Diseases spread by mosquitoes

      Mosquito has three basic body parts: head, thorax, and abdomen. The head consists of a pair of eyes, antennae to sense chemicals and the mouth parts called the palpus and the proboscis- an elongated sucking mouthpart that is typically tubular and flexible (only in females).Thorax includes two wings and 3 pair of legs. When it flies, the wing produces a humming sound. Abdomen contains the digestive and excretory organs.

      The average mosquito lifespan is less than two months. Males usually live for 10 days or less, and females can live around six to eight weeks, under ideal conditions.


      Some mosquitoes are vectors for diseases. Some of the diseases transmitted by mosquitoes include: malaria, dengue, chikungunya, yellow fever etc. These diseases are caused by bacteria, virus or parasites transmitted. These germs do not harm the mosquito but they reproduces inside the mosquito. Later, the mosquito passes the germs to other humans when biting them.


      Malaria is typically transmitted through the bite of an infected Anopheles mosquito. When a mosquito bites a person with malaria, it sucks up germs along with the blood. These germs grow in the body of mosquito in 7 to 10 days. This period is known as incubation period. Infected mosquitoes carry the Plasmodium parasite. When these mosquitoes bite the person, the parasite enters into the bloodstream of the person. This is how malaria spreads. The Plasmodium parasite (protozoa) that causes malaria is a single-celled parasite that multiplies in red blood cells of humans as well as in the mosquito intestine.

      Control of Malaria

      Water should not be allowed to collect near the house. Stagnant water serves as a breeding ground for mosquitoes.

      Using a mosquito net in areas with stagnant water sources such as lakes or non-running streams as these places are especially prone to mosquitoes.

      By wearing long pants and sleeves we can reduce the chance of getting infected.

      Spraying insecticides like DDT (dichloro diphenyl trichloroethane) in and around the house.

      Using anti malaria drugs like chloroquinine.

      Infected person should be kept in isolation.

      Diseases spread by houseflies

      Houseflies do not bite but are carrier of germs such as bacteria, virus, protozoa, and worms. They sit on garbage, feces and other dirty places. Germs sticks to their body parts and when they sit on the food item, they transfer those germs to the food. A person when eat that contaminated food falls ill.

      Housefly’s body is mainly divided into three parts (head, thorax, and abdomen), a hard exoskeleton, and six jointed legs. They have a pair of transparent wings and can taste using its feet and with its mouthparts. Houseflies usually eat liquids, but they can liquefy many solid foods with their saliva.

      Some of the diseases transmitted by mosquitoes include: hepatitis, cholera, typhoid, dysentery etc.

      Dysentery especially in the children needs the immediate attention of doctor. In this disease patient typically experience mild to severe abdominal pain or stomach cramps and passing of stool, which sometimes show mucus and blood. Untreated dysentery can be dangerous, especially if the infected person cannot replace lost fluids fast enough.

      It is most important to replace the fluids lost from diarrhea. To make up for this loss of water, ORS (Oral Rehydration Solution) is given at regular interval of time.

      It can be easily prepared at home. Ingredients includes: 6 teaspoons of Sugar, half (1/2) teaspoon of salt and one liter of clean drinking or boiled water and then cooled. Mix the dry ingredients and then and one liter of clean drinking water. Stir well and give to the patient at short intervals. Patient may be then taken to consult a doctor.

      Diseases caused by micro organisms

      Many diseases are caused by various kinds of germs which include bacteria, fungi, protozoa and viruses. These germs are too small to be seen by the naked eye. These are called microorganism or microbes.


      The study of microorganisms is called microbiology. They are present in air, water, soil, in hot spring and even in our body. Some microbes cause diseases that are transmitted from one person or animal to other.

      Diseases caused by virus: flu (influenza), common cold, measles, mumps, german measles (Rubella), smallpox, cowpox, chicken pox, HIV (can lead to AIDS), rabies etc.

      Diseases caused by bacteria: cholera, tuberculosis (TB), septicaemia ("blood poisoning"), anthrax etc.

      Diseases caused by protozoa/protoctista: Malaria, sleeping sickness, dysentery etc.

      Diseases caused by fungi: Athlete's foot, ringworm etc.


      Diseases and Prevention

      Many diseases are transmitted through direct contact with infected person such as measles, conjunctivitis, chickenpox etc. These diseases can be prevented by avoiding contact with infected person by touching or using anything used by the person such as towel, brush etc.

      Diseases like tuberculosis, common cold, whooping cough etc. are spread through air. Air borne disease can be prevented if a person suffering from disease  cover his mouth when he cough or sneeze and avoids spitting in public places.

      There are certain diseases which are caused through infected food and water. They are diarrhea, jaundice, cholera, typhoid etc. These diseases can be prevented if we adopt healthy habits such as washing hand before and after eating, washing hand with soap after the use of toilet, drinking boiled or filtered water.

      Insects like mosquito causes diseases like malaria, dengue etc. and can be prevented by keeping the surrounding clean, by spraying insecticides etc.

      How to keep good health?

      1. Avoid eating food kept open for long time as germs start growing on it and make food unfit for consumption.

      2. Do not dispose-off or litter garbage around water source as they become breeding ground for insects like mosquitoes and houseflies. These insects transmit disease to people and animals.

      3. Trim your nails as dirt under the nails may contain germs which may get transferred while eating or cooking or serving food. Maintain personal hygiene.

      4. Spray insecticides in stagnant water source.

      5. Avoid using personal items of infected person such as bed sheet, towel, cloths etc.

      6. Exercise on regular basis makes our body strong and healthy.


      7. Take adequate sleep as it refresh the body.

      8. Eat balanced diet. Balanced diet keeps the body healthy and healthy body is the best prevention against disease.

      9. Vaccination is an effective method of preventing communicable disease. Vaccines reduce the risk of infection by working with the body's natural defense system to help it safely develop immunity to disease.


    • Download to practice offline.