Effect of four antimicrobials against an Encephalitozoon sp. (Microsporidia) in a grasshopper host

Encephalitozoon cuniculi Genotype III Evinces a Resistance to Albendazole Treatment in both Immunodeficient and Immunocompetent Mice

Of four genotypes of Encephalitozoon cuniculi, E. cuniculi genotype II is considered to represent a parasite that occurs in many host species in a latent asymptomatic form, whereas E. cuniculi genotype III seems to be more aggressive, and infections caused by this strain can lead to the death of even immunocompetent hosts. Although albendazole has been considered suitable for treatment of Encephalitozoon species, its failure in control of E. cuniculi genotype III infection has been reported. This study determined the effect of a 100× recommended daily dose of albendazole on an Encephalitozoon cuniculi genotype III course of infection in immunocompetent and immunodeficient mice and compared the results with those from experiments performed with a lower dose of albendazole and E. cuniculi genotype II. The administration of the regular dose of abendazole during the acute phase of infection reduced the number of affected organs in all strains of mice and absolute counts of spores in screened organs. However, the effect on genotype III was minor. Surprisingly, no substantial effect was recorded after the use of a 100× dose of albendazole, with larger reductions seen only in the number of affected organs and absolute counts of spores in all strains of mice, implying variations in albendazole resistance between these Encephalitozoon cuniculi genotypes. These results imply that differences in the course of infection and the response to treatment depend not only on the immunological status of the host but also on the genotype causing the infection. Understanding how microsporidia survive in hosts despite targeted antimicrosporidial treatment could significantly contribute to research related to human health.

Identification of candidate agents active against N. ceranae infection in honey bees: establishment of a medium throughput screening assay based on N. ceranae infected cultured cells

Many flowering plants in both natural ecosytems and agriculture are dependent on insect pollination for fruit set and seed production. Managed honey bees (Apis mellifera) and wild bees are key pollinators providing this indispensable eco- and agrosystem service. Like all other organisms, bees are attacked by numerous pathogens and parasites. Nosema apis is a honey bee pathogenic microsporidium which is widely distributed in honey bee populations without causing much harm. Its congener Nosema ceranae was originally described as pathogen of the Eastern honey bee (Apis cerana) but jumped host from A. cerana to A. mellifera about 20 years ago and spilled over from A. mellifera to Bombus spp. quite recently. N. ceranae is now considered a deadly emerging parasite of both Western honey bees and bumblebees. Hence, novel and sustainable treatment strategies against N. ceranae are urgently needed to protect honey and wild bees. We here present the development of an in vitro medium throughput screening assay for the identification of candidate agents active against N. ceranae infections. This novel assay is based on our recently developed cell culture model for N. ceranae and coupled with an RT-PCR-ELISA protocol for quantification of N. ceranae in infected cells. The assay has been adapted to the 96-well microplate format to allow automated analysis. Several substances with known (fumagillin) or presumed (surfactin) or no (paromomycin) activity against N. ceranae were tested as well as substances for which no data concerning N. ceranae inhibition existed. While fumagillin and two nitroimidazoles (metronidazole, tinidazole) totally inhibited N. ceranae proliferation, all other test substances were inactive. In summary, the assay proved suitable for substance screening and demonstrated the activity of two synthetic antibiotics against N. ceranae.

Effect of three drugs against Encephalitozoon cuniculi infection in immunosuppressed mice

Microsporidia comprise a large group of obligate intracellular parasites. The microsporidian Encephalitozoon cuniculi causes disseminated infection in immunosuppressed patients with HIV, cancer, or transplants and in the elderly. In vivo and in vitro studies on the effectiveness of drugs are controversial. Currently, there is no effective treatment. We tested albendazole, albendazole sulfoxide, metronidazole, and cyclosporine in mice immunosuppressed with cyclophosphamide and inoculated by the intraperitoneal route with 10(7) E. cuniculi spores. One week after experimental inoculation, the mice were treated with albendazole, albendazole sulfoxide, metronidazole, and cyclosporine. Histological and morphometric analyses were performed to compare the treated groups. The state of immunosuppression was evaluated by phenotyping CD4(+) and CD8(+) T cells by flow cytometry. Nontreated mice showed acute disseminated and fatal encephalitozoonosis. The treatment with benzimidazoles significantly reduced infection until 30 days posttreatment (p.t.), but at 60 days p.t., the infection had recurred. Metronidazole decreased infection by a short time, and cyclosporine was not effective. All animals were immunosuppressed by all the experiments, as demonstrated by the low number of CD4(+) and CD8(+) T cells. We conclude that no drug was effective against E. cuniculi, but the benzimidazoles controlled the infection transiently.

Nosema ceranae escapes fumagillin control in honey bees

Fumagillin is the only antibiotic approved for control of nosema disease in honey bees and has been extensively used in United States apiculture for more than 50 years for control of Nosema apis. It is toxic to mammals and must be applied seasonally and with caution to avoid residues in honey. Fumagillin degrades or is diluted in hives over the foraging season, exposing bees and the microsporidia to declining concentrations of the drug. We showed that spore production by Nosema ceranae, an emerging microsporidian pathogen in honey bees, increased in response to declining fumagillin concentrations, up to 100% higher than that of infected bees that have not been exposed to fumagillin. N. apis spore production was also higher, although not significantly so. Fumagillin inhibits the enzyme methionine aminopeptidase2 (MetAP2) in eukaryotic cells and interferes with protein modifications necessary for normal cell function. We sequenced the MetAP2 gene for apid Nosema species and determined that, although susceptibility to fumagillin differs among species, there are no apparent differences in fumagillin binding sites. Protein assays of uninfected bees showed that fumagillin altered structural and metabolic proteins in honey bee midgut tissues at concentrations that do not suppress microsporidia reproduction. The microsporidia, particularly N. ceranae, are apparently released from the suppressive effects of fumagillin at concentrations that continue to impact honey bee physiology. The current application protocol for fumagillin may exacerbate N. ceranae infection rather than suppress it.

Encephalitozoon and Enterocytozoon (Microsporidia) spores in stool from pigeons and exotic birds: microsporidia spores in birds

Microsporidia are considered to be a cause of emerging and opportunistic infections in humans, and the species that infect humans can also infect a wide range of animals, raising concerns for zoonotic transmission. To understand the role of birds in the transmission of diseases caused by microsporidia, we examined 196 fecal specimens from birds, including birds of the families Psittacidae, Emberizidae, Icteridae and Columbidae, using Gram-chromotrope stain and polymerase chain reaction (PCR). Of the 196 fecal samples surveyed, 48 (24.5%) tested positive for microsporidia. The prevalence of microsporidia infection was higher in pigeons (31.1%) than in other birds (18.8%). The species of microsporidia that were detected in the birds surveyed in this study included Encephalitozoon hellem (found in 16.3% of positive samples), Enterocytozoon bieneusi (5.6%), Encephalitozoon intestinalis (1.5%) and Encephalitozoon cuniculi (1%). All the internal transcribed spacer (ITS) sequence of the rRNA from the study samples matched (with 100% identity) their correlate reference genotypes in GenBank, which included E. hellem 1A (AF338367), E. hellem 3 (AF110328), E. cuniculi I (AF338410) and E. bieneusi EpbA (AF076040). No fecal sample contained more than one type of microsporidian species. This study implicates exotic birds and pigeons as potential sources of microsporidia infection for humans living in urban areas.

A new Encephalitozoon species (Microsporidia) isolated from the lubber grasshopper, Romalea microptera (Beauvois) (Orthoptera: Romaleidae)

We describe a new microsporidian species, Encephalitozoon romaleae n. sp., isolated from an invertebrate host, the grasshopper Romalea microptera, collected near Weeks Island, Louisiana, and Jacksonville, Florida. This microsporidian is characterized by specificity to the gastric caecae and midgut tissues of the host and a life cycle that is nearly identical to that of Encephalitozoon hellem and Encephalitozoon cuniculi. Mature spores are larger (3.97 x 1.95 microm) than those of other Encephalitozoon species. Polar filament coils number 7 to 8 in a single row. Analysis of the small subunit (SSU) rDNA shows that E. romaleae fits well into the Encephalitozoon group and is a sister taxon to E. hellem. This is the first Encephalitozoon species that has been shown to complete its life cycle in an invertebrate host.

Testing intra-hemocelic injection of antimicrobials against Encephalitozoon sp. (Microsporidia) in an insect host

Encephalitozoon spp. are the primary microsporidial pathogens of humans and domesticated animals. In this experiment, we test the efficacy of four commercial antimicrobials against an Encephalitozoon sp. in an insect host by intra-hemocelic injection. All four antimicrobials, viz., thiabendazole, quinine, albendazole, and fumagillin, significantly reduced but did not eliminate microsporidia spore counts in the grasshopper host. Among these four drugs, thiabendazole was most effective in reducing the microsporidia spore level up to 90%, followed by quinine (70%), albendazole (62%), and fumagillin (59%). No control or quinine-treated animals died, whereas 45% of albendazole animals died. Despite the high mortality induced by albendazole, this drug significantly reduced spore counts, a result not seen in previous per os trials. Among the treatment groups, grasshoppers injected with thiabendazole lost a significant mass. Our study suggests that quinine and related alkaloids should be further examined for antimicrosporidial activity.