Microsporidia - Emergent Pathogens in the Global Food Chain

Abstract

Intensification of food production has the potential to drive increased disease prevalence in food plants and animals. Microsporidia are diversely distributed, opportunistic, and density-dependent parasites infecting hosts from almost all known animal taxa. They are frequent in highly managed aquatic and terrestrial hosts, many of which are vulnerable to epizootics, and all of which are crucial for the stability of the animal-human food chain. Mass rearing and changes in global climate may exacerbate disease and more efficient transmission of parasites in stressed or immune-deficient hosts. Further, human microsporidiosis appears to be adventitious and primarily associated with an increasing community of immune-deficient individuals. Taken together, strong evidence exists for an increasing prevalence of microsporidiosis in animals and humans, and for sharing of pathogens across hosts and biomes.

Keywords: aquaculture; farming; immune-suppression; intensive rearing; phylogeny; zoonotic.

Figure 1. Microsporidiosis in Humans

(A) Encephalitozoon hellem keratoconjunctivitis. Areas of corneal damage due to microsporidiosis (arrow). (B) Corneal scraping from a case of microsporidian keratoconjunctivitis demonstrating spores (arrow) of E. hellem. (C) Conjunctival biopsy in a case of microsporidian keratoconjunctivitis demonstrating microsporidian spores in cross-section (arrows point to polar tubes, the infective structures). The arrangement of the polar tubes is consistent with Encephalitozoon. (D) Intestinal biopsy from a patient with gastrointestinal microsporidiosis and diarrhea due to Enterocytozoon bieneusi (arrows point to spores in the apical region of an intestinal epithelial cell). (E) Stool stained with modified trichrome stain (arrows point to spores). PCR confirmed that this infection was due to E. bieneusi. (F) Intestinal biopsy from a patient with gastrointestinal microsporidiosis and diarrhea due to Encephalitozoon intestinalis.

Figure 2. Microsporidiosis in Shrimp Farming

Routine health-checking of shrimp stock throughout the production cycle (A,B) and the application of sensitive and specific diagnostics for known and emergent shrimp pathogens has revealed a host-switching event and emergence of clinical disease caused by the microsporidian parasite Enterocytozoon hepatopenaeii in Penaeus vannamei from in Asia. The parasite, congeneric with the human pathogen Enterocytozoon bieneusi, undergoes similar development within the gut of infected shrimp and is implicated in the multi-billion dollar yield-limiting condition known as early mortality syndrome (EMS).