Babesia spp. are obligate protozoan parasites of red blood cells. Transmission to humans occurs through bites from infected ticks or blood transfusion. Infections with B. microti account for the majority of the reported cases of human babesiosis in the USA. A lower incidence is caused by the more recently described species B. duncani. The current gold standard for detection of Babesia is microscopic examination of blood smears. Recent PCR-based assays, including real-time PCR, have been developed for B. microti. On the other hand, molecular assays that detect and distinguish between B. microti and B. duncani infections are lacking. Closely related species of Babesia can be differentiated due to sequence variation within the internal transcribed spacer (ITS) regions of nuclear ribosomal RNAs. In the present study, we targeted the ITS regions of B. microti and B. duncani to develop sensitive and species-specific droplet digital PCR (ddPCR) assays. The assays were shown to discriminate B. microti from B. duncani and resulted in limits of detection of ~10 gene copies. Moreover, ddPCR for these species were useful in DNA extracted from blood of experimentally infected hamsters, detecting infections of low parasitemia that were negative by microscopic examination. In summary, we have developed sensitive and specific quantitative ddPCR assays for the detection of B. microti and B. duncani in blood. Our methods could be used as sensitive approaches to monitor the progression of parasitemia in rodent models of infection as well as serve as suitable molecular tests in blood screening.

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Powassan virus (POWV) is a tick-borne flavivirus circulating in North America and the Russian Far East that can cause severe neuroinvasive diseases, including encephalitis, meningitis, and meningoencephalitis. The reported neuroinvasive case fatality is about 10%, and approximately 50% of the survivors from the neuroinfection exhibit long-lasting or permanent neurological sequelae. Currently, treatment of POWV infection is supportive, and no FDA-approved vaccines or specific therapeutics are available. A novel Powassan vaccine candidate was created using virus-like particle technology (POW-VLP) and assembled with the viral structural proteins pre-Membrane (prM) and Envelope (E). Western blot immunoassay demonstrated high antigenicity of POW-VLP structural proteins. Transmission electron microscopy indicated that the POW-VLP exhibited icosahedral morphology typical of flaviviruses. A dose-escalation study in a murine model was performed to test immunogenicity and safety. Serum antibody was tested by ELISA, demonstrating that POW-VLP afforded 100% seroconversion to the E protein. Reporter viral-particle neutralization assay demonstrated high levels of neutralizing antibodies in the serum of immunized mice. Hybridomas expressing monoclonal antibodies were produced following POW-VLP immunization. The POW-VLP vaccine candidate created in this study provides a strategy for inducing protective antibodies against Powassan neuroinvasive infection.