Infectious diseases and even certain contagious diseases spread through the following agencies. Their ways of spreading is also given along with these agencies.
1. Air-borne transmission
2. Contact transmission-direct and indirect
3. Vehicle transmission (Water, milk, food etc.)
5. Tran placental transmission
1. Air-borne Transmission:
Air is very important carrier of infectious disease. While a person breathes, coughs or sneezes, he sprays out certain infected droplets. The air carries these infected droplets away where they enter into the body of a healthy person.
Sometimes while breathing we inhale certain dust particles that are infected. These infected particles also cause certain diseases. Given below is a list of certain diseases that are spread by air:
(a) Cold and cough,
(c) Measles, Small-pox, Chicken-pox etc.
(d) Whooping cough,
2. Contact Transmission:
It is another cause, and a pertinent one for the spread of certain infectious diseases. Generally persons who look after certain patients suffer from these diseases. This contact may be of the following types:
(a) Personal contact i.e. coming in physical contact with patient. The disease agent is transmitted directly from an infected individual to a susceptible host, during physical contact. In classroom it is quite possible for a boy suffering from some infectious disease to come in contact with other boys, whom he may pass infection.
(b) Sometimes dirty hands are also responsible for carrying the germs of certain infectious diseases such as Polio Myelitis, dysentery, etc. These diseases are very common with some children and so they should be trained to keep their hands clean and free from dirt.
Given below is a list of the diseases that are contacted in this way:
(ii) Small pox,
(v) Scarlet fever,
3. Vehicle Transmission:
According to Park vehicle transmission implies transmission of the disease agent through the agency of water, ice, milk, food, serum, plasma or other biological products, of these, water is most important vehicle of transmission in many areas of the world because it is used by every one. Cholera, typhoid fever and viral hepatitis are outstanding examples of diseases transmitted by vehicle transmission.
Fly is the strongest carrier of the infection. If it sits on a food, it spoils it. At one hand it sits on the sputum of a patient and on the other hand it sits on the food. Generally it is the fly that makes the drinks infected. Sometimes dust particles also discharge this function. Given below is a list of the diseases that are caused by infected food and drinks: -
(c) Enteric fever,
(e) Scarlet fever,
(g) Tuberculosis etc.
4. Vector Transmission:
According to Park, Vectors are arthropods or other invertebrate hosts, which transmit infection by inoculation into the skin or mucosa by biting or by deposit of infective material on the skin or on food or other objects. Vectors transmit disease in two ways (a) Mechanical Transmission.
The disease agent is carried mechanically on the legs or body of the insect, e.g. diarrhea, dysentery and typhoid fever by the housefly, and (b) Biological Transmission. This may be of three types (i) Propagative. The disease agent multiplies and increases in the insect vector e.g; plague bacilli in rat fleas, (ii) Cyclo propagative the parasite undergoes a cycle of development in the body of insect host with multiplication e.g. malaria parasite in mosquito, but increase its progeny, (iii) Cycle development.
The parasite undergoes a cycle of development without multiplication e.g. filarial parasite in culex mosquito and guinea worm embryo in Cyclops.
5. Tran placental Transmission:
Some diseases have been known to be carried tran placentally from infected mother to foetus in uterus e.g., syphilis, rubella, measles, toxoplasmosis. It is not known why in some cases the foetus escapes and in others it gets infected.