388
The Biology of Sea Turtles, Vol. II
Implicit in the health assessment process is the establishment or availability
of normative data, i.e., determining the range of conditions to be found in
apparently healthy animals within a population, so that deviations can be recognized. This can include normal ranges for quantitative physical, physiologic, and
biochemical parameters as well as background frequencies (prevalence) for infections or exposures — i.e., to what agents the population is exposed. Making an
assessment requires familiarity both with disease and with what is normal. Some
parameters such as blood biochemical values can be quantitated and can be
statistically treated to define “reference ranges.” Health assessment also has
subjective aspects that are dependent on the experience of the person performing
the assessment. Health assessment also is confined to a specific time point at
which an animal is evaluated. Drawing inferences from these data about the future
health of animals or populations also requires some knowledge about the risks
associated with specific conditions.
There is no single currency for assessing health status, and therefore, assessment
of health is circumscribed by how thoroughly the patient is examined, what parameters are evaluated, and which tests are conducted for specific conditions or diseases.
Consequently, health assessments should be characterized in the most specific objective terms possible. Characterizations such as “healthy,” “sick,” or “stressed” are too
vague and impossible to interpret or compare without knowing the parameters that
were measured to define them. Furthermore, although the parameters that are
selected will provide some useful information about health status, one must remember that much information relevant to this assessment will remain unknown.
In contrast to health assessment, disease investigations have very specific goals
to further characterize disease processes and identify the cause(s), source, and contributory factors that are responsible for certain abnormal findings and diseases that
are recognized in individuals and populations. Whereas health assessment may identify problems, disease investigation seeks to understand the basis for these problems.
15.2.2 I NDIVIDUAL VS . P OPULATION H EALTH
There is a distinction between health assessments of individuals versus health assessments of populations. When discussing health assessment, one usually is referring to
individual health. Population health ultimately is dependent upon the health of individuals, but evaluating all individuals in a population is impossible. A population of
turtles at any given time will include individuals that have never been exposed to a
particular pathogen, toxin, or other disease-causing agent; individuals that have been
exposed but were resistant to infection or toxicity; individuals that were infected or
intoxicated but have fully cleared the infection or toxin and are no longer exposed;
and individuals that are currently colonized, infected, or exposed to the toxin. In the
last group of exposed individuals, some may not develop any pathology, others may
develop a disease process or have tissue damage that remains subclinical, whereas
others develop overt clinical disease, and some of these animals die. Understanding
health at the population level requires being able to detect individuals in each of these
categories, to describe their distribution over various age/stage classes at any given
time, and to detect changes in their frequency distribution over time.
1123 book.book Page 388 Monday, November 11, 2002 11:11 AM
The Biology of Sea Turtles, Vol. II
Implicit in the health assessment process is the establishment or availability
of normative data, i.e., determining the range of conditions to be found in
apparently healthy animals within a population, so that deviations can be recognized. This can include normal ranges for quantitative physical, physiologic, and
biochemical parameters as well as background frequencies (prevalence) for infections or exposures — i.e., to what agents the population is exposed. Making an
assessment requires familiarity both with disease and with what is normal. Some
parameters such as blood biochemical values can be quantitated and can be
statistically treated to define “reference ranges.” Health assessment also has
subjective aspects that are dependent on the experience of the person performing
the assessment. Health assessment also is confined to a specific time point at
which an animal is evaluated. Drawing inferences from these data about the future
health of animals or populations also requires some knowledge about the risks
associated with specific conditions.
There is no single currency for assessing health status, and therefore, assessment
of health is circumscribed by how thoroughly the patient is examined, what parameters are evaluated, and which tests are conducted for specific conditions or diseases.
Consequently, health assessments should be characterized in the most specific objective terms possible. Characterizations such as “healthy,” “sick,” or “stressed” are too
vague and impossible to interpret or compare without knowing the parameters that
were measured to define them. Furthermore, although the parameters that are
selected will provide some useful information about health status, one must remember that much information relevant to this assessment will remain unknown.
In contrast to health assessment, disease investigations have very specific goals
to further characterize disease processes and identify the cause(s), source, and contributory factors that are responsible for certain abnormal findings and diseases that
are recognized in individuals and populations. Whereas health assessment may identify problems, disease investigation seeks to understand the basis for these problems.
15.2.2 I NDIVIDUAL VS . P OPULATION H EALTH
There is a distinction between health assessments of individuals versus health assessments of populations. When discussing health assessment, one usually is referring to
individual health. Population health ultimately is dependent upon the health of individuals, but evaluating all individuals in a population is impossible. A population of
turtles at any given time will include individuals that have never been exposed to a
particular pathogen, toxin, or other disease-causing agent; individuals that have been
exposed but were resistant to infection or toxicity; individuals that were infected or
intoxicated but have fully cleared the infection or toxin and are no longer exposed;
and individuals that are currently colonized, infected, or exposed to the toxin. In the
last group of exposed individuals, some may not develop any pathology, others may
develop a disease process or have tissue damage that remains subclinical, whereas
others develop overt clinical disease, and some of these animals die. Understanding
health at the population level requires being able to detect individuals in each of these
categories, to describe their distribution over various age/stage classes at any given
time, and to detect changes in their frequency distribution over time.
1123 book.book Page 388 Monday, November 11, 2002 11:11 AM