Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 3/26/2014
Publication Date: 10/1/2014
Citation: Fayer, R., Santin, M. 2014. Chapter 3. Epidemiology of Microsporidia in humans, pp. 135-164. In Weiss, L., Becnel. J.J. (eds) Microsporidia: Pathogens of Opportunity. Wiley-Blackwell, Hoboken, NJ. 728PP. 2014.
Interpretive Summary: Microsporidia are tiny protist parasites, ubiquitous in nature and found worldwide. Of over 1,200 species of microsporidia, most infect insects, birds, and fish, but 17 species also infect humans. Virtually all species that infect humans infect animals as well. Early knowledge of microsporidian epidemiology is limited because even at the highest magnification of light microscopes the spores are difficult to identify. Microsporidian infections in humans were reported sporadically until the outbreak of HIV AIDS when microsporidia were identified by electron microscopy and gene sequencing as widespread emerging opportunistic pathogens in immunocompromised patients and then in immunocompetent persons. Human pathogenic microsporidia have been detected in companion and food animals as well as in irrigation water used for crops, recreational waters, drinking water, and effluent from wastewater treatment plants. Foodborne infection has been associated with contaminated fresh produce. Transmission can result from direct contact through broken skin, eye lesions, and sexual transmission. Species that infect insects have been found in humans, possibly transmitted through insect bites, skin lesions, or contaminated food or water. Transplacental transmission has not been documented in humans but has been reported in nonhuman primates and other mammals. This chapter summarizes the aforementioned potential sources and provides in-depth tabular listings of the species and genotypes found in water, humans, and animal hosts. These data provide a source for developing methods of prevention and treatment of microsporidial disease.
Technical Abstract: This chapter focuses on the sources and pathways of the 17 species of microsporidia known to infect humans. The major human pathogenic microsporidia such as Enterocytozoon bieneusi, Encephalitozoon hellem, Encephalitozoon cuniculi, Anncaliia algerae, Vittaforma corneae, and Encephalitozoon intestinalis are emphasized, as are their linkages, based on molecular similarities, to potential host sources. Ocular infection has been linked to trauma. Potential waterborne transmission is based on finding microsporidia in surface waters, drinking water, and recreational waters. Fresh lettuce, celery, cilantro, strawberries, raspberries, mung bean sprouts, curly lettuce and parsley leaves, as well as commercial fresh orange, lemon, sugar cane, strawberry, and mango juices have been found contaminated with spores of microsporidia. Cases of infection in the paranasal sinuses also suggest there are airborne respiratory infections. Hosts for the most frequently reported microsporidian species in humans, Enterocytozoon bieneusi, include macaques, marmosets, pigs, cattle, horses, llamas, kudus, dogs, cats, foxes, raccoons, otters, guinea pigs, beavers, rabbits, muskrats, falcons, and other birds. Insects also appear as potential sources. Analysis of specimens from these hosts by ribosomal internal transcriber spacer (ITS) nucleotide sequences has identified158 genotypes useful for tracing sources of infection. Understanding the relationships of these sources to transmission of microsporidiosis provides the data needed for prevention and treatment of disease.