Glossary of Terms
aerosolization
carrier: A person or animal, in which an infectious
agent lives, which may not itself have any observable disease (at least
at some point, and in the case of some infectious agents, not at all)
caused by carrying the agent. The carrier is the potential source of infectiondirectly
or indirectly, it is involved in transmitting the disease to humans or
animals.
cotton rat (Sigmodon hispidus)
deer mouse (Peromyscus maniculatus)
hantaviruses
infection: The entry and development of an infectious
agent in the body of a person or animal. An infection may be either apparent
(called manifest)the infected person appears to be sick, or inapparentthere
is no outward sign that an infectious agent has entered that person at
all.
Navajo Medical Traditions and HPS
Oryzomys palustris: see rice rat
Peromyscus leucopus: see white-footed mouse
Peromyscus maniculatus: see deer mouse
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 department.
reservoir: A reservoir of an infectious agent, such as
a virus, is any animal, person, plant, soil, substanceor combination
of any of these in which the infectious agent normally lives. In
addition, the infectious agent must primarily depend on the reservoir
for its survival, and must be able to multiply there. It is from the reservoir
that the infectious substance is transmitted to a human or other susceptible
host.
rice rat (Oryzomys palustris)
risk: A) The chance of being exposed
to an infectious agent by its specific transmission mechanism. B) The
chance of becoming infected if exposed to an infectious agent by its specific
transmission mechanism.
Sigmodon hispidus: see cotton rat
transmission of 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 ordinarily 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 get into 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 or the mucus membranes of the eye,
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.
Vehicle-borne transmission:
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.
Vector-borne transmission:
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, that
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 and dryness. 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 elsewhere.
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.
vector: any living creature that transmits an infectious
agent to humans.
virus
white-footed mouse (Peromyscus leucopus)
zoonotic disease or infection: An infection or infectious
disease that may be transmitted from vertebrate animals (Such as a rodent) to humans. |