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VetBooks.ir Chapter 1

Concepts in Veterinary Toxicology

Roger O. McClellan

effects, if they occur, may be manifest in a nonspecific
INTRODUCTION
manner as an increase in the incidence of common dis-
Toxicology, from the Greek words toxicon for poison and eases, such as cancer," in a population.
logos for scientific study, is the study of poisons. Wide ranges of materials are capable of producing
Veterinary medicine is that branch of medical science toxic effects when exposure occurs at sufficiently high
concerned with the diagnosis, treatment, and prevention levels. Indeed, with extreme levels of exposure most
of diseases of animals. The adjective veterinary is derived agents can produce adverse effects. For example, while
from Latin: veterinae, beasts of burden. Obviously, the both water and oxygen are required to sustain life they
modern field of veterinary medicine extends beyond the are toxic when the level of intake is excessive. The
“beasts of burden” to include all the domesticated animal nature of the toxic responses depends not only on the tox-
species, both livestock and companion animals, as well as icant but also the route of exposure, the duration and
nondomesticated species. Indeed, it has expanded to intensity of the exposure, and the characteristics of the
include nonmammalian species. The focus of toxicology exposed individual, i.e., species, gender, age, preexisting
is on chemicals, including chemicals in plants. However, disease states, nutritional status, and prior exposure to the
it is generally acknowledged that the study of effects of agent or related compounds. The exposure may be brief
ionizing radiation is a part of the field or is at least a or prolonged. The response may appear to be acute or
closely related specialty. Pharmacology, from the Greek chronic and occur soon after exposure or much later and
words pharma for drugs and logos for scientific study, is only after prolonged exposure. The response may be rela-
a closely related field concerned with the science of tively unique to the toxicant, i.e., a specific toxicosis, or
drugs: their preparation, properties, effects and uses in the distinguishable from common diseases caused by natural
diagnosis, treatment, and prevention of disease. processes or exposure to other agents. In many cases,
The field of toxicology is very broad and includes the sophisticated statistical methods are required to associate
identification and characterization of poisons, their physi- some excess health risk, such as cancer, over and above
cal and chemical properties, their fate in the body and that caused by other factors, with a particular toxicant
their biological effects. In addition, toxicology is con- exposure. This is especially true today after much prog-
cerned with the treatment of disease conditions caused by ress has been made in controlling exposure to toxic
poisons. The terms toxicant and poison are used inter- materials.
changeably. A toxicant is a material that, when it contacts In this chapter, I first provide a brief historical per-
or enters the body in sufficient quantity via ingestion, spective on the development of veterinary toxicology as a
inhalation, dermal contact, or injection, interferes with the subspecialty of the veterinary medical profession and as a
normal biological processes and causes adverse health specialized area within the general field of toxicology.
effects. The term toxin is used to describe poisons origi- This is followed by a section on the evolution of veteri-
nating from biological processes. The term toxic is used nary toxicology from an observation-based profession to
to describe the effects of a poison on biological systems. one that places increasing reliance on science developed
Toxicosis is the term used to describe the syndrome of through experimentation. This includes a discussion of
adverse health effects that result from exposure to a toxi- the risk paradigm that has become an integral part of
cant. During the last several decades, increased concern toxicology in recent decades. In the next section, I offer
has developed for the effects of long-term low-level expo- several related paradigms for acquiring, organizing, and
sures to toxicants. With these exposures, adverse health using knowledge in veterinary toxicology so as to

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