ORIGINAL PAPER Testing intra-hemocelic injection of antimicrobials against Encephalitozoon sp. (Microsporidia) in an insect host Shajahan Johny & Amanda S. Nimmo & Mark A. Fisher & Elizabeth S. Inks & Ryan M. Kirkpatrick & Philip A. Miller & Adam L. Johnson & Kanisha R. Lites & Calli C. Whitehouse & Douglas W. Whitman Received: 5 September 2008 / Accepted: 23 September 2008 / Published online: 11 October 2008 # Springer-Verlag 2008 Abstract Encephalitozoon spp. are the primary micro- sporidial 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. Introduction The microsporidia are a diverse group of eukaryotic parasites that are extremely specialized and highly derived relatives of fungi (Hibbett et al. 2007; Keeling 2003). More than 1,200 different species of microsporidia have been identified belonging to approximately 140 genera. These obligate-intracellular parasites infect members of nearly every phylum of the animal kingdom, including inverte- brates, fish, amphibians, reptiles, birds, and mammals (Didier and Weiss 2006; Visvesvara 2002; Vossbrinck and Debrunner-Vossbrinck 2005; Wittner and Weiss 1999). The microsporidia Enterocytozoon bieneusi, Encephalitozoon intestinalis, Encephalitozoon hellem, and Encephalitozoon cuniculi account for more than 90% of human micro- sporidia infections (Didier and Weiss 2006; Mathis et al. 2005). The most common clinical manifestations of human microsporidiosis are chronic diarrhea and wasting due to enteric infection, but the spectrum of disease is wide and includes most organ systems (Franzen and Muller 2001; Wittner and Weiss 1999). Infection can lead to death (Weber et al. 1997; Webster et al. 2008). Albendazole and other benzimidazoles that bind tubulin, as well as fumagillin and its derivatives that inhibit methionine aminopeptidase type 2, are the most commonly used antibiotics for the treatment of microsporidiosis; however, effective and safe treatments do not yet exist for some of the microsporidian species that infect humans (Didier et al. 2005; Didier and Weiss 2006). Consequently, new testing models, drugs, and therapies are needed (Didier et al. 2005). In previous papers (Johny et al. 2007; Johny and Whitman 2008), we proposed using an insect-microsporidia model as a rapid, inexpensive, and efficient method to screen potential antibiotics against this group of pathogens. In these previous trials, we tested different antibiotics against an Encephalitozoon sp. infecting the grasshopper Romalea microptera by oral feeding. However, oral administration of drugs is problematic because ingested antibiotics may or may not pass across the gut into the body, and this process may be altered by co-ingested food or digestive chemistry. An example is albendazole, which is relatively insoluble in water and most organic solvents, properties that influence its absorption and behavior in the Parasitol Res (2009) 104:419–424 DOI 10.1007/s00436-008-1214-y S. Johny : A. S. Nimmo : M. A. Fisher : E. S. Inks : R. M. Kirkpatrick : P. A. Miller : A. L. Johnson : K. R. Lites : C. C. Whitehouse : D. W. Whitman (*) Department of Biological Sciences, Illinois State University, Normal, IL 61790-4120, USA e-mail: dwwhitm@ilstu.edu