Neorickettsia are bacterial endosymbionts of Digenea (=endoparasitic flukes) capable of infecting the vertebrate hosts of flukes. In humans, N. sennetsu has been identified as a probable cause of unexplained, incapacitating fevers in Laos and Thailand - a region where people routinely eat raw fish and may ingest fluke parasites harboring the bacteria. There are many gaps in our knowledge about Neorickettsia and this proposal seeks to fill some of those gaps. Objectives are three-fold. First, vector incrimination studies will be conducted in N. sennetsu endemic areas of Laos to determine which of the several fluke species that parasitize the people living in the Mekong River basin harbor N. sennetsu and thus are likely vectors of N. sennetsu. Identification of the key vector fluke species involved in sennetsu transmission is a critical step towards establishing risk factors of the disease and in formulating strategies and recommendations for its prevention. Second, a large-scale screening of banked specimens of human digenean parasites, including schistosomes, will be conducted to determine the taxonomic and geographic distribution of Neorickettsia among medically important digenean species. Third, the role of horizontal and vertical transmission will be examined using a non-pathogenic species of Neorickettsia to determine how uninfected fluke lineages acquire the endosymbiont. This project will utilize undergraduate and graduate students to conduct fundamental studies on a little-studied, but potentially widespread bacterial disease agent of humans and their domestic animals. PUBLIC HEALTH RELEVANCE: Neorickettsia are bacterial endosymbionts of parasitic flukes capable of infecting the vertebrate host of the fluke and causing neorickettsial disease. Neorickettsiosis is a little-studied but potentially wide-spread disease associated with digenean parasitism of humans. Understanding its prevalence and mode of transmission will determine the severity and range of this infection and increase the awareness of neorickettsiosis as a probable cause of unexplained febrile illnesses. Correct recognition and diagnosis of neorickettsioses can lead to correct treatment (i.e., doxycycline) and relief of patient suffering.