Page 27 - parasitology for medical and clinical laboratoryprofessionals

Background of Parasitology 7

distinction between parasitology and tropical medicine, parasites might have specialized for an existence in either
the latter of which includes chiefly bacteria and viruses. man or lower animals from a common obscure origin.
Often one will find that all of these studies are conve-
niently researched by the same organization, such as the
World Health Organization, at the same time and in the Impact on Human Health
same location. There will be other references to these by Parasites
practices in this book.
Parasites occupy an important position in the history
of humans, and are an important part of morbidity and
HISTORY OF PARASITES mortality, particularly in the less developed parts of the
AFFECTING HUMANS world. Concurrently with other diseases, medical prac-
titioners are becoming more aware of the possibility of
Intestinal parasites most likely have inhabited the gas- parasitic infections that occur along with, or as a result
trointestinal tract of humans since the early beginnings of, other disease states because a number of parasite
of human habitation of the planet earth. Although it is a species are opportunistic. Anyone who has travelled to
rhetorical question, was there a reservoir for the parasites a foreign country with poor sanitary conditions for food
before they infected man? Did they originate early in the and human wastes should be evaluated for a parasitic in-
history of mankind as part of the normal intestinal organ- fection, particularly if abdominal bloating or other signs
isms that aid in digestion? Or did they possibly function and symptoms arise (Figure 1-5). In addition, migration
as an aid for stimulating immunity against pathogenic from those countries where parasites are endemic have
organisms such as some normal bacterial flora now do? brought to the shores of the United States and the en-
A plausible explanation is the possibility that parasites tire Western world a growing number of heretofore for-
adapted to life in humans after they originated in other eign pathogens which have found friendly reservoirs and
animals, with the animal being the reservoir from which hosts. Many persons are aware that a health history now
humans contracted the organism by eating the meat of almost always questions the patient as to travel within a
the animals or living in close proximity to them. And be- period of time which might yield clues as to certain in-
cause intestinal parasites that are similar to those found fections endemic in some areas of the world. Prior to the
as pathogens in humans are also found in domesticated United States becoming more advanced and prosperous,
dogs and cats as well as in other wild animals, these do- humans lived in close proximity with, and had daily con-
mesticated animals may have been the original source of tact with, farm animals, so the impact of parasitic infec-
parasitic infection (Figure 1-4). And although they dif- tions was much greater in the early history of the United
fer only slightly for the most part in speciation, these States than it is today.

Source: Centers for Disease Control and Prevention (CDC) Source: Centers for Disease Control and Prevention (CDC)

FIGURE 1-4 Dogs may have been a source for original FIGURE 1-5 Human wastes and unsanitary conditions
parasite infection in man lead to infections