Serial propagation of the microsporidian Enterocytozoon bieneusi of human origin in immunocompromised rodents

A Simian Immunodeficiency Virus-Infected Macaque Model of Enterocytozoon bieneusi Infection

Microsporidiosis caused by Enterocytozoon bieneusi is a common opportunistic infection in patients with HIV/AIDS and those on immunosuppressive therapy. A significant loss of mucosal or peripheral CD4+ T cells and subsequent dysfunction of the intestinal immune system may be responsible for the development of chronic microsporidiosis in these patients. We have used the Simian immunodeficiency virus (SIV)-infected macaque model to investigate this relationship. To establish the course of E. bieneusi infection in SIV-infected animals, four SIV-infected animals were experimentally challenged with E. bieneusi when their CD4+ counts dropped to less than 300 cells/μL of blood. Analysis of fecal samples by nested polymerase chain reaction revealed that three out of four E. bieneusi-infected macaques continued to shed spores for 7-24 months after infection, an indication of chronic microsporidiosis. Four other SIV-infected macaques, after having an initial negative phase, spontaneously acquired E. bieneusi infection when their CD4+ counts dropped to less than 600 cells/μL of blood and shed spores for 8-19 months. The shedding of E. bieneusi spores in the feces increased relative to decrease in peripheral blood CD4+ T cell numbers. Gut biopsies were obtained before and after challenge to phenotype the mucosal lymphocyte subsets using flow cytometry. The immunophenotypic analysis showed no restoration of CD4+ T cells after E. bieneusi infection in the intestinal cells. A slight increase in the percentage population of CD4+ T cells in peripheral blood did not have any effect on the control of E. bieneusi infection in the SIV-infected macaques. These preliminary studies demonstrate that SIV-infected macaques develop chronic E. bieneusi infections as their CD4+ counts dropped to below 300 cells/μL of blood.

MyD88-dependent pathway is essential for the innate immunity to Enterocytozoon bieneusi

Enterocytozoon bieneusi is clinically the most significant microsporidian parasite associated with persistent diarrhoea, wasting and cholangitis in 30-50% of individuals with HIV/AIDS, as well as in malnutritional children and in the recipients of immunosuppressive therapy. However, the host immune responses to E. bieneusi have not been investigated until recently because of lack of sources of spores, cell culture system and animal models. In this study, we purified spores from heavily infected human or monkey faeces by serial salt-Percoll-sucrose-iodixanol centrifugation, and the purity of spores was confirmed by FACS and scanning electron microscopy. Exposure of dendritic cells to E. bieneusi spores induced the upregulation of the surface markers and production of pro-inflammatory cytokines. The cytokine production was independent of toll-like receptor 4, but MyD88 dependent, because dendritic cells from MyD88 knockout mice failed to secrete these pro-inflammatory cytokines, whereas dendritic cells from C3H/HeJ (a toll-like receptor 4 mutant) were activated by E. bieneusi and secreted these cytokines. Furthermore, MyD88-deficient mice were susceptible to E. bieneusi infection, in contrast to wild-type mice that resisted the infection. Collectively, the data demonstrate innate recognition of E. bieneusi by dendritic cells and the importance of MyD88-dependent signalling in resisting infection in a murine challenge model.

Pseudoloma neurophilia infections in zebrafish Danio rerio: effects of stress on survival, growth, and reproduction

Pseudoloma neurophilia (Microsporidia) is a common disease of zebrafish Danio rerio, including those used as research models. We conducted a study comprised of 4 separate experiments to determine the effects of husbandry stress on preexisting and experimental P. neurophilia infections and the subsequent effects on survival, infection onset and intensity, fish growth, and reproduction. In fish (AB strain) with preexisting infections, stress or feeding cortisol significantly increased mortality over 7 wk compared to no stress or cortisol treatment. In contrast, no mortality was observed in fish (TL strain) experimentally exposed to P. neurophilia over 10 wk. A third experiment involved experimental exposure of AB fish to P. neurophilia and exposure to crowding and handling stressors. No mortality was associated with P. neurophilia regardless of stress treatment over a period of 20 wk. However, the onset of infection occurred sooner in stress-treated fish. Stress significantly increased the mean intensity of infection (described as xenoma area/spinal cord area in histological sections) at Week 20 post-exposure (PE). In fish with preexisting infections, myositis was significantly greater in stressed and cortisol-treated fish than those not stressed. With experimental exposure of AB fish, stressed and infected groups weighed significantly less than the control group at Week 20 PE. Regarding fecundity, the number of larvae hatched at 5 d post fertilization was negatively associated with mean infection intensity among P. neurophilia-infected and stressed AB fish. These experiments are the first to show empirically that P. neurophilia can be associated with reduced weight and fecundity, and that stress can exacerbate the severity of the infection.

Host-specific segregation of ribosomal nucleotide sequence diversity in the microsporidian Enterocytozoon bieneusi

Enterocytozoon bieneusi is a unicellular enteric fungal pathogen and the most common cause of human microsporidiosis. The frequent detection of this organism in animals, including companion animals, livestock and wildlife, has raised the question of the importance of animal reservoirs in the epidemiology of this pathogen. A partial sequence of the ribosomal internal transcribed spacer (ITS) has been widely used as a genetic marker for studying the molecular epidemiology of E. bieneusi. With the aim of comparing E. bieneusi ITS genotypes originating from different host species, and assess the potential for zoonotic transmission, E. bieneusi ITS sequences retrieved from GenBank were analyzed using two metrics of diversity, rarefaction and phylogenetic distance. In spite of the human ITS sample being geographically more diverse, ITS sequence diversity in animals exceeded that of humans. In both host groups much of the ITS diversity remains to be sampled. Using quantitative phylogenetic tests we found evidence for a partial but significant segregation of E. bieneusi ITS sequences according to host species. Host-specific segregation was confirmed by hierarchical analysis of molecular variation. To improve our understanding of the epidemiology of human microsporidiosis and strengthen the study of E. bieneusi populations, efforts to genotype additional E. bieneusi isolates from wildlife and companion animals should be prioritized and the geographic and species diversify of animal samples should be increased. Due to the possibility of genetic recombination in this species, additional unlinked genetic markers need to be developed and included in future studies.

Therapeutic evaluation of polyamine analogue drug candidates against Enterocytozoon bieneusi in a SCID mouse model

Enterocytozoon bieneusi is the most common cause of chronic diarrhea in individuals with human immunodeficiency virus infection or AIDS, and there is no effective therapy. The inhibitory activities of polyamine analogues (PG-11157, PG-11158, and PG-11302) against E. bieneusi infection were evaluated in SCID mice preconditioned with anti-gamma interferon monoclonal antibody intraperitoneally (i.p.). Mice were challenged orally with 10(4) E. bieneusi spores, and groups of mice were treated orally or i.p. 14 days later for 7 days. The inhibitory activities of the drugs against infection were determined by enumerating the E. bieneusi spores in feces three times a week by an immunofluorescence assay. Immunohistochemistry staining confirmed the infection within enterocytes. Oral administration of the analogues PG-11157 (at 150 or 75 mg/kg of body weight/day) and PG-11302 (at 250 mg/kg/day) had significant inhibitory activity (96.2 to 99.6%) that was slightly better than that of fumagillin (1 mg/kg/day; 93.7%). The inhibitory activity with i.p. injection was significant only with PG-11302 at 20 mg/kg/day. While the treatments considerably reduced the levels of spore excretion, neither polyamine analogues nor fumagillin was able to completely eliminate E. bieneusi, as excretion reappeared within 7 days after the end of treatment. Drug toxicity was apparent during treatment, but it disappeared at the end of treatment. These results warrant further examination of the analogues PG-11157 and PG-11302.

Quantitative evaluation of the impact of bather density on levels of human-virulent microsporidian spores in recreational water

Microsporidial gastroenteritis, a serious disease of immunocompromised people, can have a waterborne etiology. During summer months, samples of recreational bathing waters were tested weekly for human-virulent microsporidian spores and water quality parameters in association with high and low bather numbers during weekends and weekdays, respectively. Enterocytozoon bieneusi spores were detected in 59% of weekend (n = 27) and 30% of weekday (n = 33) samples, and Encephalitozoon intestinalis spores were concomitant in a single weekend sample; the overall prevalence was 43%. The numbers of bathers, water turbidity levels, prevalences of spore-positive samples, and concentrations of spores were significantly higher for weekend than for weekday samples; P values were <0.001, <0.04, <0.03, and <0.04, respectively. Water turbidity and the concentration of waterborne spores were significantly correlated with bather density, with P values of <0.001 and <0.01, respectively. As all water samples were collected on days deemed acceptable for bathing by fecal bacterial standards, this study reinforces the scientific doubt about the reliability of bacterial indicators in predicting human waterborne pathogens. The study provides evidence that bathing in public waters can result in exposure to potentially viable microsporidian spores and that body contact recreation in potable water can play a role in the epidemiology of microsporidiosis. The study indicates that resuspension of bottom sediments by bathers resulted in elevated turbidity values and implies that the microbial load from both sediments and bathers can act as nonpoint sources for the contamination of recreational waters with Enterocytozoon bieneusi spores. Both these mechanisms can be considered for implementation in predictive models for contamination with microsporidian spores.