Identification of a new microsporidian parasite related to Vittaforma corneae in HIV-positive and HIV-negative patients from Portugal

Microsporidiosis in Humans

Microsporidia are obligate intracellular pathogens identified ∼150 years ago as the cause of pébrine, an economically important infection in silkworms. There are about 220 genera and 1,700 species of microsporidia, which are classified based on their ultrastructural features, developmental cycle, host-parasite relationship, and molecular analysis. Phylogenetic analysis suggests that microsporidia are related to the fungi, being grouped with the Cryptomycota as a basal branch or sister group to the fungi. Microsporidia can be transmitted by food and water and are likely zoonotic, as they parasitize a wide range of invertebrate and vertebrate hosts. Infection in humans occurs in both immunocompetent and immunodeficient hosts, e.g., in patients with organ transplantation, patients with advanced human immunodeficiency virus (HIV) infection, and patients receiving immune modulatory therapy such as anti-tumor necrosis factor alpha antibody. Clusters of infections due to latent infection in transplanted organs have also been demonstrated. Gastrointestinal infection is the most common manifestation; however, microsporidia can infect virtually any organ system, and infection has resulted in keratitis, myositis, cholecystitis, sinusitis, and encephalitis. Both albendazole and fumagillin have efficacy for the treatment of various species of microsporidia; however, albendazole has limited efficacy for the treatment of Enterocytozoon bieneusi. In addition, immune restoration can lead to resolution of infection. While the prevalence rate of microsporidiosis in patients with AIDS has fallen in the United States, due to the widespread use of combination antiretroviral therapy (cART), infection continues to occur throughout the world and is still seen in the United States in the setting of cART if a low CD4 count persists.

Molecular surveillance of Vittaforma-like microsporidia by a small-volume procedure in drinking water source in Taiwan: evidence for diverse and emergent pathogens

Vittaforma corneae belongs to microsporidia, which include over 1500 species of opportunistic obligate intracellular fungi infecting almost all known animal taxa. Although outbreaks of ocular infections caused by waterborne V. corneae have been reported in recent years, little is known about the occurrence of this pathogen in aquatic environments. In this study, 50 water samples from rivers and reservoirs around Taiwan in two seasons were analyzed to explore the presence of this pathogen in natural aquatic environments. A high detection rate of Vittaforma-like amplicons (94%; 47/50) was observed in the water samples when examined by nested PCR with primer pairs specific to the small ribosomal subunit (SSU) rRNA gene. After electrophoresis, many lanes showed multiband patterns with expected molecular weights. After confirmation by DNA sequencing and by sequence alignment in the NCBI database, we identified a variety of Vittaforma-like microsporidia with weak sequence similarity, with approximately 85% identity to V. corneae, thus indicating high diversity of microsporidia in aquatic environments. Phylogenetic analysis showed clear-cut microsporidian clade classification and indicated that the most Vittaforma-like microsporidia in this study belong to clade IV and cluster into four major groups. The first group is similar to the microsporidia associated with ocular microsporidiosis. The second group is associated with the diarrheal pathogens, whereas the third and fourth groups are a novel group and a zoonotic group, respectively. This study provides abundant sequencing information, which will be useful for future molecular biological studies on microsporidia. Because microsporidia are important pathogens of animals and humans, it is urgently necessary to determine via a survey whether there are species with potential threats that have not yet been revealed.

Surveillance of Vittaforma corneae in hot springs by a small-volume procedure

Vittaforma corneae is an obligate intracellular fungus and can cause human ocular microsporidiosis. Although accumulating reports of V. corneae causing keratoconjunctivitis in both healthy and immunocompromised persons have been published, little is known about the organism's occurrence in aquatic environments. Limitations in detection sensitivity have meant a large sampling volume is required to detect the pathogen up to now, which is problematic. A recent study in Taiwan has shown that some individuals suffering from microsporidial keratitis (MK) were infected after exposure to the pathogen at a hot spring. As a consequence of this, a survey and analysis of environmental V. corneae present in hot springs became an urgent need. In this study, sixty water samples from six hot spring recreation areas around Taiwan were analyzed. One liter of water from each sample site was filtered to harvest the fungi. The positive samples were detected using a modified nested PCR approach followed by sequencing using specific SSU rRNA gene primer pairs for V. corneae. In total fifteen V. corneae-like isolates were identified (25.0% of sites). Among them, six isolates, which were collected from recreational areas B, C and D, were highly similar to known V. corneae keratitis strains from Taiwan and other countries. Furthermore, five isolates, which were collected from recreation areas A, C, E and F, were very similar to Vittaforma-like diarrhea strains isolated in Portugal. Cold spring water tubs and public foot bath pools had the highest detection rate (50%), suggesting that hot springs might be contaminated via untreated water sources. Comparing the detection rate across different regions of Taiwan, Taitung, which is in the east of the island, gave the highest positive rate (37.5%). Statistical analysis showed that outdoor/soil exposure and a high heterotrophic plate count (HPC) were risk factors for the occurrence of V. corneae. Our findings provide empirical evidence supporting the need for proper control and regulations at hot spring recreational waters in order to avoid health risks from this pathogen. Finally, we have developed a small volume procedure for detecting V. corneae in water samples and this has proved to be very useful.

Microsporidia as emerging pathogens and the implication for public health: a 10-year study on HIV-positive and -negative patients

Despite recent advances in the understanding and diagnosis of emerging microsporidian pathogens, more research is necessary to elucidate their complex epidemiology. In fact, studies that reflect true human-infecting microsporidian prevalence are still inadequate. The present 10-year study was undertaken to examine the occurrence of Microsporidia in 1989 stools, 69 urine and 200 pulmonary specimens from HIV-positive and HIV-negative patients using PCR and DNA sequencing. In stools, 12.0% were Microsporidia-positive. Prevalences of 13.9% and 8.5% were observed for HIV+ and HIV- samples, respectively. The percentage of children that were Microsporidia-positive (18.8%) was significantly higher than that of adults (10.2%). In stools, Enterocytozoon bieneusi (6.3%) and Vittaforma-like parasites (6.8%) were identified. Based on the internal transcribed spacer (ITS) region of E. bieneusi, Type IV (37.5%), Peru 6 (29.2%), D (12.5%), A (8.3%), C (6.3%) and PtEb II (6.3%) genotypes were identified. Microsporidia were detected in 1.5% and 1.0% of urine and pulmonary specimens, respectively. Encephalitozoonintestinalis was detected in urine. In pulmonary specimens, Encephalitozoon cuniculi and Vittaforma-like parasites were identified. An immunosuppressive condition and youth (children) appear to be risk factors for microsporidian infection. Microsporidia seems to have an important impact on public health in Portugal, highlighting the need to implement routine diagnosis.

Analysis of the beta-tubulin gene from Vittaforma corneae suggests benzimidazole resistance

We amplified, cloned, and sequenced the beta-tubulin gene of Vittaforma corneae, a microsporidium causing human infections. The beta-tubulin gene sequence has a substitution at Glu(198) (with glutamine), which is one of six amino acids reported to be associated with benzimidazole sensitivity. Benzimidazoles were assayed for antimicrosporidial activity and showed poor parasite inhibition.

Microsporidiosis in South Africa: PCR detection in stool samples of HIV-positive and HIV-negative individuals and school children in Vhembe district, Limpopo Province

Microsporidia were initially recognized as pathogens of insects and fish but have recently emerged as an important group of human pathogens, especially in immune-compromised individuals, such as those with HIV infection. In this study, we used a PCR-RFLP assay confirmed by quantitative real-time PCR and trichrome staining to determine the prevalence of microsporidian infections among hospital patients and school children in Vhembe region. Enterocytozoon bieneusi was the only microsporidian species detected in these stool samples. It was found in 33 (12.9%) of 255 samples from the hospitals and in 3 (4.5%) of 67 samples from primary school children and was significantly associated (P=0.039) with diarrhea in HIV-positive patients (21.6%) compared to HIV-negative individuals (9%). However, microsporidian infections were not associated with intestinal inflammation as indicated by the lactoferrin test. These results suggest that microsporidia might be a cause of secretory diarrhea in HIV-positive patients. To our knowledge, this is the first report of E. bieneusi in the Vhembe region of South Africa. Further investigations are needed in order to clarify the pathogenesis of E. bieneusi in HIV-positive patients.

Experimental meningoencephalomyelitis by Encephalitozoon cuniculi in cyclophosphamide-immunosuppressed mice

Encephalitozoonosis is an increasingly important opportunistic protozoan infection in immunocompromised individuals. This study aims to examine the development of an experimental Encephalitozoon cuniculi infection in the central nervous system of immunosuppressed mice. Adult Balb-C mice were inoculated intraperitoneally with E. cuniculi spores, treated with cyclophosphamide during the experimental period and killed from 15 to 75 days post-inoculation. Tissue samples were collected and processed for light and transmission electron microscopy investigation. Multifocal granulomas were seen in all organs. A lymphocytic, diffuse, non-suppurative menigoencephalomyelitis was observed, with neuronal degeneration and necrosis, macrophagic infiltration and reactive astrocytosis. E. cuniculi spores were seen in the microgranulomas or occurred unassociated with inflammatory reaction. The parasites were rarely seen in Hematoxylin-Eosin stained sections, but were Gram-Chromotrope positive. Proliferative forms and spores were found in parasitophorous vacuoles within neural cells and macrophages. Experimental encephalitozoonosis in immunosuppressed mice provides an useful model for the study of brain lesions associated with these protozoans in man.

Zoonotic potential of the microsporidia

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.

Interspecies transmission of Enterozytozoon bieneusi supported by observations in laboratory animals and phylogeny

Enterocytozoon bieneusi is emerging as an important cause of chronic diarrhoea in AIDS patients. Its reservoirs and transmission patterns are unknown. In this study, we have examined E. bieneusi sequences from four Rhesus macaques of different origin, which were kept at one animal facility. The sequences were identical in all animals, which suggested that infection had occurred within the facility. Full sequence agreement of E. bieneusi from macaques was found with an E. bieneusi genotype that occurs frequently in humans. To clarify, the relevance of possible inter-species transmission from man to macaque, a phylogenetic analysis was conducted including all sequences of E. bieneusi deposited in GenBank. The hitherto used system of diverse nomenclatures could be reduced to an outlier group and three main lineages, one of which could be further sub-divided into five subgroups. Based in this phylogeny, an association of parasites and host species could be observed for main lineages 2 and 3, as well as for most of the subgroups of main lineage 1. For confirmation, the phylogeny of main lineage 1 was reconstructed with an alternative method of distance estimation, yielding essentially the same parasite-host associations. Zoonotic potential of E. bieneusi is thus supported on a phylogenetic basis.