Introduction into Parasitic Protozoa
Parasitic protozoans are protists—i.e., unicellular eukaryotes. Besides, they share the common features of being heterotrophic, motile in at least one of their stages, and dependent on a host for survival. Protists are a highly diverse evolutionary unrelated grouping that is at present taxonomically divided into at least five supergroups or eukaryotic kingdoms: SAR, Excavata, Amoebozoa, Archaeplastida, and Ophistokonta. The protozoan parasites that infect farm animals and pets, and are the subject of this book, belong to the first three supergroups. These organisms can cause significant morbidity and mortality in domestic animals, thus provoking substantial economic losses associated with livestock production or major concern for pet owners. Additionally, some are zoonotic and of public health relevance. Human domestication has led to a huge world population of a few selected farm and pet animals, usually raised in close proximity. This has provided an ideal and spacious ecological niche for parasitic protozoans that invade and thrive in these hosts. In addition, international travel has promoted global distribution of most parasitic protozoa. A long history of coadaptation has existed between parasites and their wild ancestor hosts, whereas adaptation to domestic animals has been much shorter from an evolutionary perspective. While the first scenario resulted in unapparent infections that ensured parasite perpetuation, the second represents an unbalanced situation resulting in clinical signs and mortality. This calls for continuous efforts in the development and application of control measures.
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