MEANS OF DISEASE TRANSMISSION (MODE OF TRANSMISSION)
a. Physical (Direct) Contact. Certain diseases are spread by physical contact
with an infected person. Examples are syphilis, gonorrhea, and scabies.
b. Indirect Contact.
(1) Droplets, air, and dust. Droplets are vehicles by which a disease may
be transmitted from an infected person to susceptible persons. When an infected
person coughs, sneezes, or even talks, he spreads droplets containing disease germs.
If other persons are close to the infected person, they may inhale some of these
droplets. Furthermore, some germs expelled from the respiratory tract are extremely
small and light in weight and may remain suspended in the air for hours or may be
resuspended in dust. Inhalation of these germs by susceptible persons may also result
in disease. Many of the respiratory diseases are transmitted in these ways.
(2) Fomites. Articles contaminated with disease germs from an infected
person may become vehicles of disease transmission if a susceptible person uses
them. Examples of fomites are contaminated clothing, bed linen, and eating utensils.
c. Arthropods or Other Vectors. Flies, fleas, mosquitoes, ticks, mites, and lice
are among the arthropods that spread disease from person to person or from animal to
person. Insects are involved in both the direct and the indirect transmission of disease.
A mosquito, for example, can pick up disease germs when it bites a person sick with a
disease such as malaria. Later, when the mosquito bites another person, it injects the
disease germs. The mosquito is, therefore, the vector by which the disease is
transmitted from one person directly to another person. The fly, on the other hand,
transmits disease germs indirectly. It can pick up disease germs on its body when it
comes in contact with filth and may deposit these germs on food. If a person eats this
food, he may become ill.
d. Water and Food. Certain disease germs are transmitted through the
consumption of foods such as raw fish and improperly cooked meat and poultry.
However, most of the diseases that are transmitted by food and water are the result of
contamination of the food or water with feces or other infectious material from a person
or animal. If water or food so contaminated is not properly treated, the germs therein
may infect the consumer. Outbreaks of disease will occur when personal hygiene and
proper sanitation practices applicable to food handling, water purification, water
disposal, and the control of flies and other vermin are not properly observed and
enforced. Among the diseases usually transmitted by contaminated food or water are
typhoid fever, infectious hepatitis, cholera, dysentery, and food poisoning (due to
staphylococci, Clostridium perfringens, and other organisms.)
SUSCEPTIBLE PERSON (HOST)
A susceptible or non-immune person is one who has little resistance against a
particular organism and who, if exposed to this organism, is likely to contract disease.
By contrast, an immune person is one who has a high degree of resistance to the
organism and who, when exposed, does not develop the disease. Immunity to many
diseases is relative and can be overcome by sufficient exposure to the diseases. The
term host is used to connote the living body upon which or in which a disease agent or
parasite lives--the final recipient of an infectious agent. The susceptibility of a host to
invasion by infectious agents is dependent upon a number of factors.