Zoonotic potential of the microsporidia - PubMed (original) (raw)

Review

Zoonotic potential of the microsporidia

Alexander Mathis et al. Clin Microbiol Rev. 2005 Jul.

Abstract

Microsporidia are long-known parasitic organisms of almost every animal group, including invertebrates and vertebrates. Microsporidia emerged as important opportunistic pathogens in humans when AIDS became pandemic and, more recently, have also increasingly been detected in otherwise immunocompromised patients, including organ transplant recipients, and in immunocompetent persons with corneal infection or diarrhea. Two species causing rare infections in humans, Encephalitozoon cuniculi and Brachiola vesicularum, had previously been described from animal hosts (vertebrates and insects, respectively). However, several new microsporidial species, including Enterocytozoon bieneusi, the most prevalent human microsporidian causing human immunodeficiency virus-associated diarrhea, have been discovered in humans, raising the question of their natural origin. Vertebrate hosts are now identified for all four major microsporidial species infecting humans (E. bieneusi and the three Encephalitozoon spp.), implying a zoonotic nature of these parasites. Molecular studies have identified phenotypic and/or genetic variability within these species, indicating that they are not uniform, and have allowed the question of their zoonotic potential to be addressed. The focus of this review is the zoonotic potential of the various microsporidia and a brief update on other microsporidia which have no known host or an invertebrate host and which cause rare infections in humans.

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Figures

FIG. 1.

FIG. 1.

Electron micrograph of the developmental stages of the microsporidian species Encephalitozoon cuniculi in a host cell-derived vacuole in in vitro-cultivated human fibroblast cells. K, nucleus of host cell; M, meront; P, sporont, which divides into two sporoblasts; B, sporoblast (2 μm in length), with cross sections of the polar tube; S, mature spore.

FIG. 2.

FIG. 2.

Dendrogram generated from the small subunit ribosomal RNA (ssrRNA) gene of microsporidian species identified in humans (underlined) and selected other species (Kimura's distance, unweighted pair group method of analysis). Known animal hosts are indicated in brackets; the brewer's yeast Saccharomyces cerevisiae serves as an outgroup. No corresponding gene sequences are known for the human-infecting microsporidian species Pleistophora ronneafiei, Trachipleistophora anthropophthera, Brachiola (formerly Nosema) connori, B. vesicularum, Nosema ocularum, Microsporidium ceylonensis, and M. africanum (Table 1).

FIG. 3.

FIG. 3.

Dendrogram of ITS sequences of human-infecting E. bieneusi genotypes (confirmed in independent studies) and selected genotypes with animal hosts. All sequences are deposited in GenBank with the same designations (Kimura's distance, unweighted pair group method of analysis).

FIG. 4.

FIG. 4.

Rabbit with torticollis (head tilt) due to cerebral infection with E. cuniculi.

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