Scrub typhus is caused by Orientia tsutsugamushi, an obligated intracellular bacterium that affects over one million people per year. Several mouse models have been used to study its pathogenesis, disease immunology, and for testing vaccine candidates. However, due to the intrinsic differences between the immune systems in mouse and human, these mouse models could not faithfully mimic the pathology and immunological responses developed by human patients, limiting their value in both basic and translational studies. In this study, we have tested for the first time, a new humanized mouse model through footpad inoculation of O. tsutsugamushi in DRAGA (HLA-A2.HLA-DR4.Rag1KO.IL2RγcKO.NOD) mice with their human immune system reconstituted by infusion of HLA-matched human hematopoietic stem cells from umbilical cord blood. Upon infection, Orientia disseminated into various organs of DRAGA mice resulted in lethality in a dose-dependent manner, while all C3H/HeJ mice infected by the same route survived. Tissue-specific lesions associated with inflammation and/or necroses were observed in multiple organs of infected DRAGA mice. Consistent with the intracellular nature of Orientia, strong Th1, but subdued Th2 responses were elicited as reflected by the human cytokine profiles in sera from infected mice. Interestingly, the percentage of both activated and regulatory (CD4+FOXP3+) human T cells were elevated in spleen tissues of infected mice. After immunization with irradiated whole cell Orientia, humanized DRAGA mice showed a significant activation of human T cells as evidenced by increased number of human CD4+ and CD8+ T cells. Specific human IgM and IgG antibodies were developed after repetitive immunization. The humanized DRAGA mouse model represents a new pre-clinical model for studying Orientia-human interactions and also for testing vaccines and novel therapeutics for scrub typhus.

Chlamydial infections in crocodiles have been described in several countries and in several different species. These are typically associated with severe pharyngitis and conjunctivitis, with death occurring secondary to compromise of the upper respiratory tract due to obstruction of the trachea. A population of ranched Siamese crocodiles in central Thailand experienced an epizootic of sudden death in juvenile animals. The affected animals had fulminant systemic disease primarily involving the liver and spleen but also affecting the kidneys, heart, and the whole of the respiratory tract. Chlamydia sp. were noted in liver and spleen during histopathological examination and confirmed with transmission electron microscopy and polymerase chain reaction (PCR). The sequence of the PCR product suggested a novel Chlamydia sp. of Siamese crocodiles. Crocodile farming represents an important economy in several parts of the world. Epizootics, such as the one described in this manuscript in association with Chlamydia sp., can have devastating impact on the industry and represent a potential zoonosis of significant public health concern. This is the first report of Chlamydia sp. and Aeromonas sobria causing systemic disease in crocodiles as well as the first histopathological and ultrastructural description of Chlamydia infection in Siamese crocodiles.

Attractive toxic sugar baits (ATSBs) can be an effective vector control tool, especially in areas where aerial or aquatic applications of pesticides are undesirable or impractical. In general, there is a need to develop novel or alternative insecticides for vector control, and there is a demand from consumers for more ‘natural’ pest control products. Sodium ascorbate (SA) is a naturally occurring antioxidant compound, found in fruits and vegetables, and is available commercially in the United States as a food additive and supplement. In this study, we continuously exposed groups of adult Aedes aegypti (L.), Anopheles stephensi Liston (Diptera: Culicidae), Phlebotomus papatasi Scopoli, and Lutzomyia longipalpis (Lutz & Neiva; Diptera: Psychodidae) to ATSBs containing SA in concentrations of 6, 8, 10, and 20%, and tracked their mortality over 10 d. We also exposed insects to a 20% SA–ATSB on a single day to determine the effect of a single exposure to the bait on mortality. Concentrations of ≥8% SA significantly reduced survival of both mosquito species over 10 d compared with sugar-fed controls. Sand fly mortality was inconsistent. A single exposure to 20% SA significantly reduced the survival of An. stephensi. Mosquitoes exposed to SA exhibited elevated catalase levels and cell death. The use of SA in ATSBs may be most effective in areas where sugar sources are scarce, and where mosquito species frequently sugar-feed. SA sugar baits may be a particularly attractive option for the general public looking to control mosquito populations using ‘natural’ alternatives to synthetic insecticides.