Microsporidia, enigmatic parasites

Abstract

Microsporidia are widespread, obligate intracellular parasites of most phyla and are recognized as a cause of emerging infections in humans. Unusual among eukaryotes in certain characteristics, they have been regarded as primitive eukaryotes on the basis of morphological features and molecular phylogenies. However, recent phytogenies based on protein data,’ and similarities such as the presence of chitin, trehalose and characteristics of nuclear division, suggest an evolutionary relationship with fungi. Though the phylum is characterized by a great diversity of morphologies and life cycle strategies, the characteristic that unifies all members of the phylum is their unique and highly specialized infection strategy due to the production of spores containing a coiled structure known as the polar filament, or polar tube. There are three distinct phases in the development of microsporidia: the infective (environmental) phase represented by mature spores, the proliferative phase (merogony) responsible for the massive increase in number of the parasite, and the sporogonic phase (sporogony), in which sporonts produce sporoblasts that mature into spores. In this paper, the current views on the phylogenetic position, and the morphological features and development of some micro‐sporidian species, particularly those infecting humans, are reviewed.

Key words:

• Microsporidia
• Life cycle
• Infective phase
• Proliferative phase
• Sporogonic phase