Wax Moth Galleria Mellonella Larvae as a Model to Study Rickettsia Infection

Rickettsia infections comprise an increasing number of cases of tick-borne diseases worldwide. These diseases may be fatal; however, there are few effective biologicals targeting Rickettsia. In vivo studies for Rickettsia are difficult due to strict regulations associated with the use of vertebrate laboratory animals. The purpose of this project was to evaluate susceptibility of Greater Wax Moth, Galleria mellonella larvae (GML) to infection with Rickettsia. GML were infected with 104 to 107 plaque-forming units of Rickettsia philipii 364D, or R. rickettsii Sheila Smith and kept at 34°C for 120 hours. Control groups included untreated larvae and larvae injected with K36 buffer. Infected and control GML were examined daily to record their appearance and viability. Hemolymph was collected and tested to measure Rickettsia DNA copy numbers using SYBR-Green PCR assay. Rickettsia rickettsii caused a dose-dependent lethal infection in GML. Larvae infected with less-virulent R. philipii survived but exhibited dose-dependent morphological changes. Rickettsia were detected in the hemolymph and hemocytes of infected GML by PCR and microscopy, respectively, at each point of infection. Our study demonstrated the susceptibility of GML to Rickettsia of differing virulence. GML is a novel system for studying host-cell interactions and cellular and humoral responses to rickettsiae