Protozoa

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Chapter: Pharmaceutical Microbiology : Protozoa

Parasitism is a specific type of interaction between two organisms that has many features in common with other infectious processes, but host–parasite interactions often operate over a longer timescale than those seen with other pathogens.


PROTOZOA

 

Introduction

Parasitism

 

Parasitism is a specific type of interaction between two organisms that has many features in common with other infectious processes, but host–parasite interactions often operate over a longer timescale than those seen with other pathogens. This extended process results in significant host– parasite interaction at the cellular and organismal level. It is known, for example, that some parasites alter the behaviour of the host, while others, such as Giardia lamblia, induce biochemical change in the host cells at the site of infection (the duodenal epithelium).

 

Most parasites have a life cycle that often involves several hosts; this means that survival and transmission between different hosts requires the parasite to exhibit more than one physiologically distinct form.

 

Habitats

 

Parasites inhabit a wide range of habitats within their hosts. Some parasites will inhabit only one site throughout their life cycle, but many move to various sites within the body. Such movement may require the formation of motile cellular forms, and it will produce a significant change in the physiology and morphology of the parasite as a result of environmental change. Parasites moving from the gut to other tissues, for example, will encounter  higher levels of oxygen, changes in pH and significant exposure to the host immune response. When life cycles involve more than one host organism these changes are greater. The reasons why parasites move to various sites in with the host is driven by evasion of host immune attack and to aid transmission.

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