Page 16 - parasitology for medical and clinical laboratoryprofessionals

xiv PREFACE

life in societies throughout the world. This book is also ORGANIZATION OF THE
intended to alert the laboratory worker, regardless of TEXTBOOK
professional level, as to the possibility of endemic areas
developing within the more developed countries, due A topical overview is presented in the early portions of
to the prevalence of world travel. It can also be used as this book to acquaint the student of laboratory medicine
a resource for any medical professional for consultation to the background and history of the early knowledge of
when familiarizing oneself with or exploring topics of parasites and the growing body of knowledge in diagnos-
human parasitology. Modes of transmission due to con- ing and handling of parasitic infections. An emphasis is
taminated soil, water, and food sources require that the placed on the morphological characteristics of the most
health care professional be familiar with conditions that common parasites encountered in the clinical laboratory
contribute to contraction of parasitic infections. today. The epidemiology of parasitic infections and con-
The common perception is that only certain areas ditions that give rise to these medical diseases is stressed
of the world suffer from large-scale parasitic infections, early in the textbook.
and that there are only a limited number of the various Microorganisms as causative intestinal parasites
species that are capable of infecting humans. This is far are classified as five different groups, those of flagellates,
from the truth, as more than 300 species of helminths ciliates, amoebae, coccidia, and microsporidia. Tissue
have been recorded as the causative organism for these protozoa are numerous and include blood and other
infections. Parasitologists and pathologists have knowl- tissues. These protozoa are mostly intracellular but may
edge of the most common parasites that inhabit the diges- border on being extracellular as some do not invade the
tive tract along with associated organs of digestion such cytoplasm. Several chapters are devoted to the “worms”
as the liver. However, the laboratory professional is the of the intestinal tract, and include nematodes (round-
medical worker who would most likely come into routine worms), cestodes (tapeworms), and trematodes (flukes).
contact with specimens such as blood and feces or spu- Tissue parasites, which invade muscle and nerve
tum that may contain eggs of parasites or the actual or- tissues, are also important causative agents in diseases
ganism. Therefore, it is mandatory that when performing of humans. Mites and lice are also scourges of mankind,
parasitological procedures, the health care professional infecting the skin and hair of those infected. Life cycles,
become familiar with the most common organisms that identification, and treatment of these various infestations
affect humans. No less important than this knowledge is are systematically covered in this book.
the fact that proper collection, transport, and treatment It is not sufficient to only be able to identify para-
of specimens in order to find evidence that a parasitic sites from their basic structures. In order to control po-
infection is present are mandatory to effectively provide tential epidemics of parasitic infections, it is necessary to
accurate results. be knowledgeable of the hosts and intermediate hosts for
The numbers of parasitic organisms found in nature, stages of these organisms. Vectors are necessary for some
and those that may become parasitic, are staggering. Even of the parasitic organisms to be transmitted to humans.
algae, though non-parasitic, has been found to produce These stages are important to be able to identify, in order
epidemic diarrhea. Exotic parasites enter this country on to properly prepare specimens and to determine the pres-
a daily basis, and cause little or no signs or symptoms in ence of an infection by parasites. In addition, it is often
their hosts, but become a problem when spread in this necessary to gather as much information as possible con-
country. Zoonotic infections, or those that result from cerning a patient’s recent travel history, food preferences
transmission by a vector, such as nematode parasites of or routine diet, outdoor activities that may expose the per-
animals, accidentally infect humans around the world. son to infection, and to unusual environmental exposure.
Fortunately, many of these show few signs in their hu-
man hosts, and eventually die in the tissues of the infected Procedures for Identifying
persons. But it is possible that some of these will adapt Parasitic Organisms
and will become “new” sources of infections in the years
ahead. And to further complicate the situation, nonpara- Direct identification involves direct visual observation
sitic entities also morphologically resemble parasites and of a parasite from a properly prepared and frequently
are confused with parasites. stained preparation. The eggs of the more common