|
|
Definitions
Disease
“Lack of ease.”
Departure from the state of health or normality. Disease is a process,
not a thing, and represents the responses of the body to injury or insult.
Although health and disease are concepts that do not easily lend themselves
to simple definition, diseases have certain characteristics that are definable,
for example:
- Chronic -
of long duration
- Acute -
of short duration. Often quick death is implied in insects.
- Contagious
- infectious diseases, result of pathogen invasion, reproduction, and
subsequent infection of other individuals.
- Deficiency -
lack of essential elements for growth and maturity.
-
-
The
number of infectious propagules administered per measure of body weight.
True doses are rarely used in insect pathology because adjustments
are seldom made to accommodate weight differences between individual
experimental animals.
-
-
The number of infectious propagules administered to each experimental animal.
Regardless of weight, each animal in a treatment receives the same number
of infective units. This is the method by which most experimental insects
are inoculated.
-
-
Organisms growing in or on the bodies of insects; usually connotes a parasitic or other intimate symbiotic relationship.
-
-
Insectivorous; the consumption of insects and their parts.
-
-
Associations
between insects and other organisms, e.g. plant microorganisms,
Protozoa, and nematodes.
Means "Insect loving."
-
-
The study of the dynamics of diseases in populations of animals.
-
-
Transmission of a pathogen
from infected individuals to conspecific individuals within a generation
or overlapping generations in a season.
-
-
The number
of new cases of a particular disease that occurs within a stated time
period. This measurement is very rare in entomology because dead individuals
cannot easily be found and counted as diseased. The term is often incorrectly
synonymized with prevalence.
-
-
The living
in or on a host by metazoan parasites, for example, an infestation
of flies by mites. Some authors limit the term "infestation" to
cases where the parasite is visible without the use of a microscope.
-
Invasion
is the entry of a microorganism into the host body (e.g. actual penetration
of the integument, gut epithelial cells, etc.). “Primary invasiveness” is
a property of pathogenic microorganisms.
Infection is also the
introduction or entry of a pathogenic microorganism into a susceptible
host, whether or not it causes pathological effects or disease, but
implies that the organism must enter the body of the host, usually the
cells, and be able to reproduce to form new infective units. Simply
ingesting a pathogen does not imply infection.
IC50/ID50
The median infective
concentration or dose produces infection in 50% of the treated
subjects.
The median lethal concentration or dose produces death in 50% of the subjects. Usually a time period is stated, e.g. number of days post inoculation.
The median lethal time
is the time required to produce death in 50% of the infected individuals
exposed to a specific dosage of pathogens.
Inapparent
infection; the pathogen is in a nonreproductive phase
and a pathogen-host equilibrium is established. This term
is reserved to qualify "infection",
not a pathogen- e.g. an infection is latent; a virus
is occult.
Pathogenicity and Virulence
- Pathogenicity
is the ability of an organism to invade
the host and cause disease. This term is applied to groups
or species
of microorganisms,
whereas virulence is used to compare
the degree of pathogenicity within the group or species. For
example, nuclear
polyhedrosis
viruses are highly pathogenic to their
lepidopteran hosts. The wild type isolate of Lymantria
dispar NPV is more
virulent than
the "few polyhedra" mutant found in laboratory
cultures.
-
- The percentage
of hosts in a population with a specific disease at a given time
(percentage of infected individuals in the total population at a
selected time.)
-
- Multiplication
of microorganisms in the blood. Septicemia is often secondary to wounds
or to the massive reproduction of another pathogen. Host tissues are
disrupted and entry of facultatively pathogenic bacteria into the hemocoel
is allowed.
-
Transovarial (or transovarian) transmission
- Transmission from one generation to the next via the egg. The pathogen is transmitted within the ovary of the infected female and usually is found in the cells of the embryo.
-
- Transmission from one generation to the next via the egg. The pathogen can be on the surface of the egg and ingested upon hatch of the neonate host, or can be within the host embryo (transovarial transmission). Transovarial transmission is a special case of transovum transmission.
-
- Transmission of a pathogen from one generation of host to the next.
|
