Thailand – What are Microsporidians?
If you’re a shrimp farmer and have not yet read the Network of Aquaculture Centres in Asia-Pacific’s (NACA) report on Enterocytozoon hepatopenaei (EHP), a disease caused by a microsporidian parasite (http://www.enaca.org/), I recommend that you read it before you read this item. One farm manager told me that EHP might turn out to be more devastating than early mortality syndrome (EMS)! The Thai shrimp farming industry’s slow recovery from EMS is probably associated with the presence of EHP.
According to Wikipedia, microsporidia constitute a phylum of spore-forming unicellular parasites. They were once thought to be protists, but are now known to be fungi. Loosely 1,500 of the probably more than one million microsporidia have been named. They are restricted to animal hosts, and all major groups of animals host microsporidia. Most infect insects, but they are also responsible for common diseases of crustaceans and fish.
Microsporidia lack motile structures, such as flagella, and produce highly resistant spores capable of surviving outside their host for up to several years. Spore morphology is useful in distinguishing between different species. Spores of most species are oval or shaped like a flame or pear, but rod-shaped or spherical spores are not unusual.
Photomicrographs of Enterocytozoon hepatopenaei tubule epithelial cells of the hepatopancreas of Penaeus monodon. (A) H&E-stained smear of hepatopancreatic tissue showing numerous microsporidian spores (arrows). (B) Fresh preparation of microsporidian spores from a Percoll gradient. (C and D) Hepatopancreatic tissue sections showing acidophilic, granular inclusions in the cytoplasm of tubule epithelial cells (arrows). (E) Semi-thin section of hepatopancreatic tissue showing early and late plasmodia (inset a) and mature spores (inset b) in the cytoplasm of tubule epithelial cells. Some spores show unstained spots that represent their concave surfaces at one end (inset b). A, haematoxylin stain; C, Trichrome stain; D, H&E stain; E, Toluidine blue stain. ePm, early plasmodium; lPm, late plasmodium. (Somjintana Tourtip et al., 2009)
TEM of sporogonial stages of E. hepatopenaei development in hepatopancreatic tubule epithelial cells of P. monodon. (A) Early sporogonial plasmodium containing nuclei (asterisks), clear vesicles (inset a, arrowhead), and precursors of polar filaments (inset a, arrows; and inset b). (B) Sporogonial plasmodium with peripherally located sporoplasm (asterisk). (C) Sporogonial plasmodium with several peripherally located pre-sporoblasts (asterisks). (D) Plasmodial membrane showing a microvillus-like structure surrounded by host-cell cytoplasm (arrow) containing extensive RER (arrowhead). (E) Thickened plasmodial plasmalemma showing vesicular structures at the interface with host cytoplasm (arrowhead). (F) Late sporogonial plasmodium showing assembled pre-sporoblasts, polar filaments and a dense cap (arrowhead). (Somjintana Tourtip et al., 2009)
Sources: 1. Wikipedia. Microsporidia. Website visit on November 28, 2014. 2. Bob Rosenberry, Shrimp News International, November 29, 2014. – Somjintana Tourtip et al., 2009