M. Taylor – Veterinary Parasitology (4th edition, 2016)

Описание

Part 1 contains expanded individual parasite descriptions and
taxonomic status within three new chapters on Veterinary helminthology
(Chapter 1), Veterinary protozoology (Chapter 2) and
Veterinary entomology (Chapter 3). As with previous editions of
Veterinary Parasitology, further updated chapters include Laboratory
diagnosis of parasitism (Chapter 4), Antiparasitics (Chapter 5),
The epidemiology of parasitic diseases (Chapter 6) and Host resistance
to parasitic diseases (Chapter 7). Host species chapters have
been retained and updated and are now in Part 2 of the edition.
Additional information on non-obligate ectoparasites that may be
found on several hosts are grouped in a separate chapter, Facultative
parasites and arthropod vectors (Chapter 17). In keeping with
the third edition of Veterinary Parasitology, extensive indexing and
cross-referencing are provided throughout this edition.
There are several slightly different definitions of parasitism and
parasites. In the context of this book parasites are considered as
organisms which live for a considerable portion of their lives in
(endoparasites) or on (ectoparasites) another different kind of
organism, the host. Ectoparasites are also frequently vectors of
pathogens that may cause disease. Parasites are dependent on that
host and benefit from the association, at the host’s expense. They
derive nutrition from the host and may also gain other benefits
such as a protected habitat in which to grow and reproduce. Parasites
are generally harmful to their host, although this is not always
easy to demonstrate as an individual parasite may cause no recognisable
damage. Disease is frequently a population phenomenon,
with small numbers of parasites having no discernible impact but
large numbers causing effects ranging from subclinical damage to
debilitating fatal disease. Damage to the host may also results from
the host’s defence mechanisms reacting to the presence of parasites.
Many parasites are entirely dependent upon a specific host or hosts
in order to complete their life cycle and survive and these organisms
are known as an obligate parasite of that particular host. Where
an organism can either survive or complete its life cycle independently
from a host, or can have a parasitic existence, then it is called
a facultative
parasite. There are instances where for various reasons
parasites become established in hosts other than their definitive host
and in which they cannot complete their normal life cycle. These
hosts are termed accidental hosts and in the case of some zoonotic
parasites of veterinary importance, humans are an example.
Every parasite must have at least one host in its life cycle and
many species have several hosts. The host in which the parasite
is best adapted and in which it develops to an adult or sexually
mature stage and reproduces is known as the definitive, primary
or final host. If there is only a single host in the life cycle, then
transmission is said to be direct and the parasite to have a direct
life cycle. Many parasites have more complex life cycles with additional
hosts in which essential development to a new parasite stage
occurs. These stages either do not reproduce or if they do then it is
by asexual multiplication. These hosts are known as intermediate
or transitional hosts. Some of these hosts can also be vectors (such
as ticks, mosquitoes), which carry and spread disease-causing parasites
from one host to another. These life cycles with more than
one host are known as indirect or complex life cycles. There are
some parasites that use additional hosts to overcome adverse environmental
conditions or to increase the likelihood that the parasite
will be transmitted to the definitive host. There is no further development
of the parasite in these hosts. They are known as paratenic
or transport hosts.