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Abstract Pacific Coast tick fever is a recently described zoonotic disease in California caused by a spotted fever group rickettsia, Rickettsia rickettsii subsp. californica (formerly Rickettsia 364D) and transmitted by the Pacific Coast tick, Dermacentor occidentalis. Like many emerging vector-borne diseases, knowledge regarding the transmission cycle, contribution from potential amplifying hosts, and geographic distribution of R. rickettsii californica is limited. We paired molecular analysis with comparative spatial niche modeling to identify vertebrate hosts potentially involved in the transmission cycle of this pathogen. We identified R. rickettsii californica DNA in three mammal species (Otospermophilus beecheyi, Lepus californicus, and Sylvilagus audubonii). This is the first record of R. rickettsii californica detected in mammals and may indicate potential amplifying hosts for this human pathogen. Species niche modeling of uninfected and infected D. occidentalis identified areas of high suitability along the coast and Sierra Nevada foothills of California. These findings support the hypothesis that amplifying host(s) may support higher infection prevalence in the infected tick regions compared to other parts of the tick’s range. Potential host species distribution models (SDMs) were constructed from museum records and niche overlap statistics were used to compare habitat suitability with R. rickettsii californica-infected tick SDMs. We found higher than null overlap of infected ticks with California ground squirrels (O. beecheyii) and trending, but nonsignificant, overlap with two lagomorph species. Pairing molecular and niche modeling may be a useful approach to identify species that are involved in the maintenance of emerging tick-borne zoonoses.
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Sporulation Potential of Phytophthora ramorum Differs Among Common California Plant Species in the Big Sur Region
Sudden oak death (SOD), caused by the generalist pathogen Phytophthora ramorum, has profoundly impacted California coastal ecosystems. SOD has largely been treated as a two-host system, with Umbellularia californica as the most transmissive host, Notholithocarpus densiflorus less so, and remaining species as epidemiologically unimportant. However, this understanding of transmission potential primarily stems from observational field studies rather than direct measurements on the diverse assemblage of plant species. Here, we formally quantify the sporulation potential of common plant species inhabiting SOD-endemic ecosystems on the California coast in the Big Sur region. This study allows us to better understand the pathogen’s basic biology, trajectory of SOD in a changing environment, and how the entire host community contributes to disease risk. Leaves were inoculated in a controlled laboratory environment and assessed for production of sporangia and chlamydospores, the infectious and resistant propagules, respectively. P. ramorum was capable of infecting every species in our study and almost all species produced spores to some extent. Sporangia production was greatest in N. densiflorus and U. californica and the difference was insignificant. Even though other species produced much less, quantities were nonzero. Thus, additional species may play a previously unrecognized role in local transmission. Chlamydospore production was highest in Acer macrophyllum and Ceanothus oliganthus, raising questions about the role they play in pathogen persistence. Lesion size did not consistently correlate with the production of either sporangia or chlamydospores. Overall, we achieved an empirical foundation to better understand how community composition affects transmission of P. ramorum.
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- Award ID(s):
- 1753965
- PAR ID:
- 10327979
- Date Published:
- Journal Name:
- Plant Disease
- Volume:
- 105
- Issue:
- 8
- ISSN:
- 0191-2917
- Page Range / eLocation ID:
- 2209 to 2216
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1094/PDIS-03-20-0485-RE
