Document Type : Review Paper
Author
Faculty of Biology, Belarusian State University, Minsk, Republic of Belarus
Abstract
Parasites can have a wide range of adverse effects on the health and fitness of their hosts, including a decrease in host individuals (impaired host fitness) through acute or chronic disease, a decrease in the number of offspring produced by a host individual (impaired host fecundity) by affecting egg production or infant survival, and a change in the behavior of a host individual through alterations in interactions with their immediate environment or other hosts. These four parasite effects have all been conclusively demonstrated in multiple wild vertebrate populations. In addition to their effects on host individuals, parasites can influence host populations in varying ways. Extensive case studies have demonstrated that parasitism could likely account for a considerable proportion of the regulation exerted on host populations and that nature itself has evolved to rely on infection as a major player in maintaining species diversity and the structure of ecosystems. It can appear, therefore, that parasites routinely negatively affect their hosts in a rather stark relationship. However, as with nearly any natural process, host-parasite interactions can be seen as complex and is rarely a permanent state. This complexity arises from the various mechanisms via which hosts can resist or tolerate parasitic infections, or through which parasites can evade or prevent host defenses. Likewise, a multitude of factors in the environment, such as the aforementioned climate change but also habitat degradation, fragmentation or use, as well as the wildfires necessary in many ecosystems, can all new infectious diseases in wildlife.
Keywords
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