ICSE BoardEnglish MediumSTD 8BIOLOGYHealth and Hygiene4 Marks
Question
Explain the various ways by which communicable diseases spread.
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Answer
Communicable diseases are diseases that can be passed by an infected person to a healthy person either directly or indirectly. These diseases are also called infectious diseases. The communicable diseases spread from an infected person to a healthy person in the following ways. Airborne diseases $–$ Many diseases of respiratory tract are transmitted through the air. Bacteria and viruses that infect the nasal passage, throat, windpipe and lungs, are present in saliva and mucus. A sneeze or a cough sprays droplets with germs into the air.
Droplet infection is a serious health problem. When people cough and sneeze in public places, they spray droplets of saliva into the air for others. Common cold, influenza, measles, tuberculosis, diptheria, whooping cough and chickenpox are some respiratory diseases whose germs are transmitted through air.
Waterborne diseases $–$ Typhoid, dysentery, cholera and hepatitis are some infections that spread through water polluted with sewage. Drinking dirty water or using it to brush teeth or using ice made from unclean water leads to spread of waterborne diseases. Infections of ears, nasal passage and throat commonly spread through water in swimming pools.
Footborne diseases $–$ Although cooking destroys many bacteria and other germs, most of the intestinal infections are caused by food. Fresh vegetables and fruits if eaten raw without washing them thoroughly can lead to stomach infections causing vomiting and diarrhoea. Consuming of stale, rotten and unhygienically stored food also causes food poisoning.
Canned food also contains certain bacteria which cause severe intestinal infections and food poisoning. Botulism is a kind of food poisoning that results from consumption of canned food. The bacteria gain entry into the cans, multiply in the absence of air and release toxic substances which are harmful for the nervous system.
Milk can also be a source of infection if it is not boiled properly before drinking. These days pasteurized milk is available in the market. In this process, milk is boiled for thirty minutes and is chilled immediately to kill germs. Meat which is not properly cooked can also carry larvae of worms which cause diseases.
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