Molecular Epidemiology of Human Microsporidiosis Caused by Enterocytozoon Bieneusi

Enterocytozoon bieneusi is a common human pathogen, responsible for more than 90% of overall human microsporidian infections. The epidemiology of E. bieneusi infections, however, is not well studied, and little is known about its transmission routes. Enterocytozoon bieneusi-like spores have been reported in surface and ground water in the United States and France, and a possible outbreak of microsporidiosis involving 200 persons was associated with drinking water in France. Recently, genotyping tools based on DNA sequencing of the internal transcribed spacer of the rRNA gene have been used in elucidating E. bieneusi transmission. Studies conducted in Europe (Switzerland, France, Germany, and UK) and Uganda identified nine E. bieneusi genotypes in humans. A more recent study in Peru with a larger sample size confirmed the presence of three of the nine genotypes in humans, but also found eight other genotypes that have not been found in humans before. As expected, geographic differences are present in the distribution of E. bieneusi genotypes in humans, with genotype B being the predominant genotype in Europe and genotype A the most common genotype in Peru. Four of the human-pathogenic genotypes have been found in domestic animals and wild mammals, and many of the 40 or so Enterocytozoon genotypes identified in animals are genetically related to the human-pathogenic genotypes, indicating that zoonotic transmission of E. bieneusi is possible. Nevertheless, host-adapted Enterocytozoon spp have been found in dogs, cattle, and some wild mammals (muskrats and raccoons), which do not have apparent public health significance. Further studies of E. bieneusi transmission in humans and animals in other regions should be helpful to elucidate the epidemiology of microsporidiosis. internal transcribed spacer of the rRNA gene have been developed to genotype E. bieneusi isolates from humans and animals, which has helped to clarify some issues related to the transmission of E. bieneusi in humans (Rinder et al, 1997; Liguory et al, 1998; Breitenmoser et al, 1999; Buckholt et al, 2002; Sulaiman et al, 2003b). E. BIENEUSI INFECTION IN HUMANS Enterocytozoon bieneusi was first identified as a human pathogen at the beginning of the AIDS epidemic (Desportes et al, 1985). Since then, it has been shown to be a major cause of chronic diarrhea in HIV-positive persons, with infection rates varying widely among different studies, even though most studies have reported rates between 10 and 30% in AIDS patients with chronic diarrhea. Low CD4+ cell count is a major risk factor for E. bieneusi infection in HIV-positive persons, with most infected patients having CD4 cell counts lower than 100 cells/μl (Navin et al, 1999). Other risk factors for E. bieneusi infection are not clear, but a study conducted in Zimbabwe showed an association of E. bieneusi infection in AIDS patients with living in rural areas, consumption of nonpiped water, contact with cow dung, and household contact with an individual with diarrhea (Gumbo et al, 1999). No significant seasonal variation in the prevalence of INTRODUCTION Among the 14 or so human-pathogenic microsporidia species, Enterocytozoon bieneusi is the most common. It is one of the common causes of chronic diarrhea in AIDS patients (van Gool et al, 1995), and has recently been detected in HIV-negative persons (Lores et al, 2000a). In addition to causing human disease, it has also been frequently found in many animals, especially mammals (del Aguila et al, 1999; Lores et al, 2002a). Little is known about the transmission routes of human microsporidiosis. Nevertheless, humanpathogenic microsporidia have been reported in surface and ground water in the United States (Dowd et al, 1998). In France, a municipal water supply was suspected as the source of a possible outbreak of microsporidiosis involving 200 persons (Cotte et al, 1999), and spores of E. bieneusi were detected in river water (Sparfel et al, 1997; Fournier et al, 2000). Recently, several DNA sequencing tools based on the Correspondence: Lihua Xiao, Division of Parasitic Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30341, USA. Tel: +1-770-4884840; Fax: +1-770-4884454 E-mail: [email protected]