Host Range Assays

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The methods and results for host range assays are as follows. Helicosporidium sp. and doses were adjusted accordingly. The dose, resulting infection rate and number of replicates for each species were: Anopheles albimanus (5.0 x 10⁴, 58.3%, N=1), An. quadrimaculatus (5.0 x 10⁴, 100%, N=3), Ae. taeniorhynchus (3.5 x 10², 14.3%, N=1), Cx. quinquefascaitus (5.0 x 10⁵, 0%, N=2) and M. domestica (7.8 x 10⁸, 80%, N=1). The IC₅₀ (95% Fiducial Limits) for An. quadrimaculatus was 1.0 x 10⁴ (3.1 x 10³, 3.6 x 10⁴ cysts/ml). All susceptible species supported in vivo replication of the Helicosporidium sp. Culex quinquefasciatus larvae had a relatively high mortality level (40.0 ± 31.8 %) but none of the larval or adult survivors were infected. Filamentous cells were observed in the gut lumina of An. quadrimaculatus and Cx. quinquefasciatus within 1 hr after exposure indicating that barriers to infection in Cx. quinquefasciatus occurred after cysts dehisced. Examination of tissues with phase-contrast microscopy confirmed that cyst production occurred primarily in the haemocoel of An. quadrimaculatus larvae. Light microscopy of the Helicosporidium sp. in An. quadrimaculatus revealed that the main multiplicative phase began 3-4 days post challenge and was soon followed by cyst production.