Below you will find
an alphabetical listing of common terms used in articles in the Special
Pathogen Branch web site. These terms occur frequently in epidemiological
and health prevention literature.
B C D E
F G H I J K L M N
O P Q R S
T U V W X Y Z
List of Terms
A fine mist or spray which contains
Proteins produced by an organism's immune system to recognize foreign
Any substance that stimulates an immune response by the body. The immune
system recognizes such substances as being foreign, and produces cellular
antibodies to fight them. Antigen/antibody response is an important part
of a person's immunity to disease.
A quantitative or qualitative evaluation, or test, of a substance.
Frequently used to describe tests of the presence or concentration of
infectious agents, antibodies, etc.
Specific combinations of work practices, safety equipment, and facilities,
which are designed to minimize the exposure of workers and the environment
to infectious agents. Biosafety level 1 applies to agents that do
not ordinarily cause human disease. Biosafety level 2 is appropriate for
agents that can cause human disease, but whose potential for transmission
is limited. Biosafety level 3 applies to agents that may be transmitted
by the respiratory route which can cause serious infection. Biosafety
level 4 is used for the diagnosis of exotic agents that pose a high risk
of life-threatening disease, which may be transmitted by the aerosol route
and for which there is no vaccine or therapy.
A person or animal that harbors a specific infectious agent without visible
symptoms of the disease. A carrier acts as a potential source of
The number of cases of a disease ending in death compared to the number
of cases of the disease. Usually expressed as a percentage. While deaths
from other diseases are often expressed as mortality rates, SPB normally
uses case-fatality proportions. This is due to the fact that rates include
a time determinant - for example, 100 deaths per 1000 cases per year.
However, the diseases SPB works with break out sporadically, and occur
as brief epidemics.
ratio or proportion:
The number of cases of a disease (in humans) compared to the number of
infections with the agent that causes the disease (in humans).
rat (Sigmodon hispidus)
mouse (Peromyscus maniculatus)
Formally speaking, a disease is the condition in which the functioning
of the body or a part of the body is interfered with or damaged. In a
person with an infectious disease, the infectious agent that has entered
the body causes it to function abnormally in some way or ways. The type
of abnormal functioning that occurs is the disease. Usually the body will
show some signs and symptoms of the problems it is having with functioning.
Disease should not be confused with infection.
A technique that relies on an enzymatic conversion reaction. It is
used to detect the presence of specific substances, such as enzymes, viruses,
antibodies or bacteria.
Disease that is widespread in a given population.
A disease which is constantly present in the animal community, but only
occurs in a small number of cases.
The occurrence of cases of an illness in a community or region which is
in excess of the number of cases normally expected for that disease in
that area at that time.
An outbreak or epidemic of disease in animal populations.
An organism in which a parasite lives and by which it is nourished.
One of many antibodies present in blood serum which is usually indicative
of a recent or remote infection. IgG is most prevalent about 3 weeks
after an infection begins.
One of many antibodies present in blood serum which is usually indicative
of an acute infection.
A type of assay in which specific antigens are made visible by the use
of fluorescent dye or enzyme markers.
The entry and development of an infectious agent in the body of a person
or animal. In an apparent "manifest" infection, the infected
person outwardly appears to be sick. In an inapparent infection, there
is no outward sign that an infectious agent has entered that person at
all. For example, although humans have become infected with Ebola-Reston,
a species of Ebola virus, they have not shown any sign of illness. By
contrast, in recorded outbreaks of Ebola hemorrhagic fever caused by Ebola-Zaire,
another species of Ebola virus, severe illness followed infection with
the virus, and a great proportion of the case-patients died. Infection
should not be confused with
rat (M. erythroleucus or M. huberti)
An infection occurring in a patient which is acquired at a hospital or
other healthcare facility. Commonly called a cross infection.
report of a disease:
An official report that notifies an appropriate health authority of the
occurrence of a disease in a human or in an animal. Human diseases usually
are reported first to the local health authority, such as a county health
Any person, animal, arthropod, plant, soil or substance in which an infective
agent normally lives and multiplies. The infectious agent primarily depends
on the reservoir for its survival.
rat (Oryzomys palustris)
A) The chance of being exposed to an infectious agent by its specific
B) The chance of becoming infected if exposed to an infectious agent
by its specific transmission mechanism.
transcriptase polymerase chain reaction):
Powerful technique for producing millions of copies of specific parts
of the genetic code of an organism so that it may be readily analyzed.
More specifically, RT-PCR produces copies of a specific region of complementary
DNA that has been converted from RNA. The technique is often used
to help in the identification of an infectious agent.
The ongoing systematic collection and analysis of data and the provision
of information which leads to action being taken to prevent and control
an infectious disease.
infectious agents (such as a virus):
Any mechanism through which an infectious agent, such as a virus, is spread
from a reservoir (or source) to a human being. Usually each type of infectious
agent is spread by only one or a few of the different mechanisms.
There are several
types of transmission mechanisms:
a) Direct transmission:
This type of transmission is, at base, immediate. The transfer of the
infectious agent is, as the name implies, directly into the body. Different
infectious agents may enter the body using different routes. Some routes
by which infectious diseases are spread directly include personal contact,
such as touching, biting, kissing or sexual intercourse. In these cases
the agent enters the body through the skin, mouth, an open cut or sore,
or sexual organs. Infectious agents may spread by tiny droplets of spray
directly into the conjunctiva (the mucus membranes of the eye), or the
nose or mouth during sneezing, coughing, spitting, singing or talking
(although usually this type of spread is limited to about within one meter's
distance.) This is called droplet spread.
b) Indirect transmission:
Indirect transmission may happen in any of several ways:
In this situation, a vehiclethat is, an inanimate object or material
called in scientific terms a "fomite"becomes contaminated
with the infectious agent. The agent, such as a virus, may or may not
have multiplied or developed in or on the vehicle. The vehicle contacts
the person's body. It may be ingested (eaten or drunk), touch the skin,
or be introduced internally during surgery or medical treatment. Examples
of vehicles that can transmit diseases include cooking or eating utensils,
bedding or clothing, toys, surgical or medical instruments (like catheters)
or dressings. Water, food, drinks (like milk) and biological products
like blood, serum, plasma, tissues or organs can also be vehicles.
When researchers talk about vectors, often they are talking about insects,
which as a group of invertebrate animals carry a host of different infectious
agents. (However, a vector can be any living creature that transmits
an infectious agent to humans.)
Vectors may mechanically
spread the infectious agent, such as a virus or parasite. In this scenario
the vectorfor instance a mosquito contaminates its feet
or proboscis ("nose") with the infectious agent, or the agent
passes through its gastrointestinal tract. The agent is transmitted
from the vector when it bites or touches a person. In the case of an
insect, the infectious agent may be injected with the insect's salivary
fluid when it bites. Or the insect may regurgitate material or deposit
feces on the skin, which then enter a person's body, typically through
a bite wound or skin that has been broken by scratching or rubbing.
In the case of
some infectious agents, vectors are only capable of transmitting the
disease during a certain time period. In these situations, vectors play
host to the agent. The agent needs the host to develop and mature or
to reproduce (multiply) or both (called cyclopropagative). Once the
agent is within the vector animal, an incubation period follows during
which the agent grows or reproduces, or both, depending on the type
of agent. Only after this phase is over does the vector become infective.
That is, only then can it transmit an agent that is capable of causing
disease in the person.
c) Airborne transmission:
In this type of transmission, infective agents are spread as aerosols,
and usually enter a person through the respiratory tract. Aerosols are
tiny particles, consisting in part or completely of the infectious agent
itself, which become suspended in the air. These particles may remain
suspended in the air for long periods of time, and some retain their ability
to cause disease, while others degenerate due to the effects of sunlight,
dryness or other conditions. When a person breathes in these particles,
they become infected with the agentespecially in the alveoli of
the lungs. (see also "aerosolization")
How do infectious
aerosols get into the air?
Small particles of many different sizes contaminated with the infective
agent may rise up from soil, clothes, bedding or floors when these are
moved, cleaned or blown by wind. These dust particles may be fungal sporesinfective
agents themselvestiny bits of infected feces, or tiny particles
of dirt or soil that have been contaminated with the agent.
Droplet nuclei can
remain in the air for a long time. Droplet nuclei are usually the small
residues that appear when fluid emitted from an infected host evaporates.
In the case of the virus causing hantavirus pulmonary syndrome, the rodent
carriers produce urine. The act of spraying the urine may create the aerosols
directly, or the virus particles may rise into the air as the urine evaporates.
In other situations, the droplets may occur as an unintended result of
mechanical or work processes or atomization by heating, cooling, or venting
systems in microbiology laboratories, autopsy rooms, slaughterhouses or
Both kinds of particles
are very tiny. Larger droplets or objects that may be sprayed or blown
but that immediately settle down on something rather than remaining suspended,
are not considered to belong to the airborne transmission mechanism. Such
sprays are considered direct transmission.
A carrier which transmits infective agent from one host to another.
hemorrhagic fever (also spelled as viral haemorrhagic fever and referred
to as VHF)
A minute infectious agent.
mouse (Peromyscus leucopus)
An infection or infectious disease that may be transmitted from vertebrate
animals (such as a rodent) to humans.