… And Now Microsporidiosis

This is the decade of emerging infectious diseases. It seems that a “new” disease or an infectious cause for old diseases is being announced at astounding rates. Microsporidiosis is one such infection. Microsporidian infection in humans, usually those with immune deficiencies, were infrequently reported before the acquired immunodeficiency syndrome (AIDS) epidemic [1, 2]. Microsporidia are now being increasingly recognized as important opportunistic pathogens in human immunodeficiency virus (HIV) infection. Microsporidiosis has also been described in immunocompetent hosts [3]. Diseases caused by the different microsporidia that infect humans include diarrhea, keratoconjunctivitis, disseminated disease, hepatitis, myositis, kidney and urogenital infection, ascites, cholangitis, and asymptomatic carriage [1, 2]. Knowledge of the epidemiology of microsporidiosis in humans is limited, but as with cryptosporidiosis, microsporidiosis is probably a common, self-limited or asymptomatic infection in immunocompetent hosts. The high prevalence of antibodies to microsporidia (such as Encephalitozoon) in many serosurveys supports this view [1, 2].

Microsporidia are obligate intracellular, spore-forming parasites infecting every major animal group, especially insects, fish, and mammals [1, 2, 4]. They are sufficiently unique to be classified in a separate phylum, Microspora [1, 2]. Within the phylum are dozens of genera and hundreds of species [4].

Microsporidia have a life cycle consisting of three phases: a proliferative phase, the spore production phase (sporogonial phase), and the spore or infective phase [1, 2]. The spore is characteristic for the phylum (Figure 1) in that it is unicellular, with a resistant spore wall, one nucleus or two abutted nuclei (diplokaryon), sporoplasm, an anchoring disk, and an extrusion apparatus consisting of a single polar tube with an anterior attachment complex [1, 2, 4]. Although spores are environmentally resistant, they may be killed by exposure for 30 minutes to 70% ethanol, 1% formaldehyde, or 1% hydrogen peroxide …