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Question 15 Marks
Describe the ways in which communicable diseases are transmitted through various indirect methods.
Answer
Indirect methods of transmission of communicable diseases :
$1.$Using items used by the infected persons : The healthy persons may be infected by using the articles like towel, hankey, utensils, bedding used by the patient infected by the communicable diseases. Diseases like tuberculosis, ring worm; common cold, influenza are transmitted by this method.
$2.$Contaminated food and water : Diseases like dysentery, cholera spread through the contaminated food and water. Flies sitting on the food, if taken by a healthy person may be infected by the germs which may cause vomiting and loose motions. Similarly water and food infected by entamoeba may cause dysentery to persons who may take contaminated food.
$3.$Vectors or carriers : Organisms like mosquitoes and house flies, ticks carry germs from the source of infection and pass on the germs to the normal persons and thus they are infected by diseases like malaria, cholera, plague. These organisms which carry the disease are called vectors and are not infected themselves.
Mosquitoes suck blood and carry the disease causing protozoans from infected persons to healthy persons.
Similarly houseflies carry the germs from garbage and sewage to the food. If this food is taken by the persons they become prey to typhoid and other diseases.
$4.$Air : One sneeze from a person infected by cold may give billions of germs which are carried by air and may infect the healthy person. Tuberculosis passes from one person to other by coughing or sneezing of the infected person.
These germs remain suspended in the air and persons may be infected by these spores or germs. Common cold, measles, diptheria, chicken pox.
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Question 25 Marks
What is vaccination? Mention the four ways in which vaccine’s are prepared, giving the name of one disease for which each type of vaccine is used.
Answer
For developing resistance in the body we introduce germs or germ substances in the body to develop resistance in the body against a particular disease. The material introduced into the body is called vaccine, this practice is called prophylaxis.
The germ or the germ substance is put into the body orally as polio drops or it is introduced by injection as $\text{TAB}$ vaccine. Vaccine or vaccination was attached with small pox, but it is now used in a general sense.
$1.$Preparation :
Killed germs are introduced into the body These act as vaccine for $\text{TAB}$, vaccine for typhoid, Salk’s vaccine for poliomyelitis. Rabies vaccine for dog bite.
$2.$Living weakened germs : The living germs are treated in such a way that they become very weak and as such, they cannot cause the disease. They can induce antibody formation such as the vaccine for measles and the freezed dried $\text{BCG}$ vaccine for tuberculosis.
$3.$Living fully virulent germs : These virulent germs in small doses are introduced into the body as vaccine and these produce antibodies in the body and these do not allow the germs of particular type to cause that disease: In this vaccination the person is inoculated with cowpox virus. It is very similar to small pox virus.
$4.$Toxoids : Toxoids are prepared from the extracts., of toxins secreted by bacteria. These toxins are poisons and these are made harmless by adding formalin into them. They retain their capacity and as a result when introduced into the body they produce antibodies into the body and do not allow the germs to grow in the body as vaccines for diphtheria and tetanus.
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[5 Mark Question Answer] - BIOLOGY STD 8 Questions - Vidyadip