BSC 310 Lecture Notes - Lecture 33: Prodrome, Arthropod, Fomite
Knowing How Infectious Disease Spreads
Infectious diseases are those caused by microorganisms. In order to relate a particular
organism to a particular disease, Koch's postulates must be fulfilled. First devised by
Robert Koch in the 1870s, Koch's postulates are a series of procedures for identifying
the cause of a particular disease. They are described in the first chapter of this book.
Symptoms and signs. Infectious diseases are usually characterized by changes in body
function known as symptoms. Symptoms are subjective changes not always apparent to the
observer. The patient may also exhibit signs, which are objective changes that can be
measured. Fever and a skin rash are examples of signs. When a specific group of symptoms
or signs accompanies a disease, the group is called asyndrome.
Transmission and incidence. Infectious diseases may be classified according to
theirtransmissibility. A disease that spreads from one host to another is a communicable
disease. Those communicable diseases transmitted with particular ease are said to
becontagious. Diseases not spread between hosts are noncommunicable.Staphylococcal food
poisoning is an example.
The incidence of a disease refers to the percent of a population that contracts it over a
particular period. The prevalence of a disease, by contrast, is the percentage of a population
having the disease at a particular time.
When a disease occurs only occasionally, it is called a sporadic disease. A disease present in
a population at all times is an endemic disease. A disease that breaks out in a population in a
short period is an epidemic disease, and an epidemic disease occurring throughout the world
is a pandemic disease.
Types of disease. Diseases can be defined in terms of their severity and duration. Anacute
disease occurs rapidly and lasts a short time, while a chronic disease develops slowly and
lasts a long time. Influenza is an acute disease, while tuberculosis is a chronic disease.
A subacute disease is a disease that has vague symptoms and lasts a relatively long time.
A latent disease remains inactive in a host for a time and then becomes active.
Infections can be described as local infections if they are restricted to a small area of the
body and systemic infections if they spread throughout the body systems. The presence of
multiplying microorganisms in the blood is septicemia. Toxins present in the blood
constitute toxemia.
Infectious diseases may also be described as primary diseases or secondary diseases.
Aprimary disease is the first illness that occurs, and a secondary disease is due to an
opportunistic microorganism, often a normal resident, after the body's defenses have
weakened.
Modes of disease transmission. When a disease remains in a population, a source of
pathogens called a reservoir of infection exists within the population. The reservoir can be
human, animal, or nonliving, such as the soil. A human reservoir who has had the disease
and recovered but continues to shed infectious organisms is called acarrier. Animal diseases
spread to humans are called zoonoses.
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Document Summary
In order to relate a particular organism to a particular disease, koch"s postulates must be fulfilled. Robert koch in the 1870s, koch"s postulates are a series of procedures for identifying the cause of a particular disease. They are described in the first chapter of this book. Infectious diseases are usually characterized by changes in body function known as symptoms. Symptoms are subjective changes not always apparent to the observer. The patient may also exhibit signs, which are objective changes that can be measured. Fever and a skin rash are examples of signs. When a specific group of symptoms or signs accompanies a disease, the group is called asyndrome. Infectious diseases may be classified according to theirtransmissibility. A disease that spreads from one host to another is a communicable disease. Those communicable diseases transmitted with particular ease are said to becontagious. Diseases not spread between hosts are noncommunicable. staphylococcal food poisoning is an example.
