Habitat fragmentation changes community structure and diversity in many biological systems. These same changes can also affect the maintenance and transmission dynamics of zoonotic diseases including vector-borne ones such as Lyme disease. Ongoing research in the Swei lab is investigating the impact of habitat fragmentation on vertebrate, invertebrate, and microbial species communities. 

Relevant papers: 

• Lilly, M.; Amaya-Mejia, W.; Pavan, L.; Peng, C.; Crews, A.; Tran, N.; Sehgal, R.; Swei, A. 2022. Local Community Composition Drives Avian Borrelia burgdorferi Infection and Tick Infestation. Vet. Sci. 9, 55. 

• Salomon, J., Crews, A., Lawrence, A., Swei, A. 2021 Host infection and community composition predict vector burden. Oecologia,

• Sambado, S., Salomon, J., Crews, A., Swei, A. 2020. Mixed transmission modes promote persistence of an emerging tick-borne pathogen. Ecosphere 11(6): e03171. https://doi.org/10.1002/ecs2.3171 

• Lawrence, A.M., O'Connor, K.E., Swei, A. 2018. Patterns of diversity along a habitat size gradient in a biodiversity hotspot. Ecosphere 9 (4): e02183. Open Access Link; https://doi.org/10.1002/ecs2.2183

• MacDonald, A., Hyon, D.W., Brewington, J.B., O'Connor, K., Swei, A., Briggs, C. 2017. Lyme disease risk in  southern California: abiotic and environmental drivers of Ixodes pacificus (Acari: Ixodidae) density and  infection prevalence with Borrelia burgdorferi. Parasites and Vectors.. 10: 7.

• ​​MacDonald, A.J., Hyon, D.W., McDaniels, A., O'Connor, K.E., Swei, A., Briggs, C.J. 2018. Risk of vector tick exposure initially increases then declines through time in response to wildfire in California. Ecosphere 9(5):e02227.

New Funding! CDC Center of Excellence in Vector borne Diseases for the Pacific Southwest region (PacVec) has been renewed for another 5 years of funding! As part of the leadership team, PI Swei will lead studies to mitigate the risk of tick-borne diseases using community ecology informed approached to vector management and reservoir host control. Trials are underway to test the efficacy of host-targeted vaccines to reduce the density of infected, host-seeking ticks in the wild. 

Ticks are the most important disease vector in the Northern hemisphere and transmit Lyme disease in addition to other pathogens. Ongoing research in the lab includes investigating the role of the tick microbiome in pathogen transmission and vector-competency. With the use of next generation deep sequencing, we have been exploring the microbial community of several species of ticks such as the Lyme disease vector, Ixodes pacificus, as well as other species: Dermacentor occidentalis, Ixodes angustus, Haemaphysalis leporispalustris.

Investigations of the tick microbiome has revealed surprising patterns governing the development of the tick microbiome and potential impacts on pathogen transmission. One key finding is that blood meal host identity plays a significant role in structuring the microbiome Ixodes pacificus. These impacts on microbiome composition and structure appears to influence the vector competency of I. pacificus for B. burgdorferi. 

Relevant papers: 

• Couper, L.I., Kwan, J.Y., Ma, J., Swei, A. 2019. Drivers and patterns of microbial community assembly in a Lyme disease vector. Ecology and Evolution, 9(2): 7768-7779.  DOI: 10.1002/ece3.5361

• Couper, L.I. and Swei, A. 2018. Tick microbiome characterization by next-generation 16S rRNA amplicon sequencing. Journal of Visualized Experiments 138: e58239. DOI: 10.3791/58239.   

• Kwan, J., Griggs, R., Chicana, B., Miller, C., Swei, A. 2017. Vertical versus horizontal transmission of the    microbiome in a key disease vector. Molecular Ecology. 26 (23): 6599-6761. DOI: 10.1111/mec.14391

• Swei, A. and J. Kwan. 2017. Tick microbiome and pathogen acquisition altered by host blood meal. The  International Society for Microbial Ecology. 11: 813-816

• ​Bouquet, J., Melgar, M., Swei, A., Delwart, E., Lane, R.S. and Chiu, C.Y. 2017. Metagenomics of the Pacific Coast tick, Dermacentor occidentalis, in northwestern California, 2011-2014. Nature Scientific Reports. 7: 12234.

Vector-borne zoonotic diseases (VBZD) are emerging globally. Swei lab and collaborators  conducted a meta-analysis of patterns, drivers, and evolutionary contexts for this group of diseases. We found that hard ticks (Ixodidae) and mosquitoes (Culicidae) are responsible for vectoring the vast majority of emerging VBZD. (Swei et al., in review)

​In addition to the Lyme disease pathogen, ticks transmit many other pathogens. Detailed epidemiological studies of tick vectors and their animal reservoirs are essential to better characterize and prevent these diseases, many of which are emerging.

One emerging disease that we are working to better characterize is babesiosis. The vector and reservoir hosts of this potentially fatal and blood-transfusion transmitted disease are unknown. In collaboration with the California Department of Public Health and the California Department of Fish and Wildlife, we recently published epidemiological studies to identify the vector and reservoir of the etiological cause of babesiosis in the western United States, Babesia duncani. Current research in the lab also uses spatial modeling approaches to help identify hotspots of risk for emerging tick-borne diseases and to predict likely pathogen reservoirs for zoonotic diseases like Rickettsia 364D.

Relevant papers:

• Paddock, C.D., Slater, K., Swei, A., Zambrano, M.L., Kleinjan, J.E., Padgett, K.A., Saunders, M.E.M., Andrews, E.S., Trent, E., Zhong, J., Sambado, S., Goldsmith, C.S., Pascoe, E.L., Foley, J., Lane, R.S., Karpathy, S.E. 2022. Detection and isolation of Rickettsia tillamookensis (Rickettsiales: Rickettsiaceae) from Ixodes pacificus (Acari: Ixodidae) from multiple regions of California. Journal of Medical Entomology. 59 (4): 1404-1412​

• Schmeller, D.S., Cheng, T., Shelton, J. Lin, C.F., Alvarado, A.C., Bernardo-Cravo, A., Zoccarato, L. Ding, T.S., Yu, A., Lin, Y.P., Swei, A. Fisher, M, C., Vredenburg, V.T., Loyau, A. 2022. Environment is associated with chytrid infection and skin microbiome richness in an amphibian biodiversity hotspot. Scientific Reports, 12; 16456.

• Swei, A., Couper, L.I., Coffey, L.L., Kapan, D., Bennett, S. 2020. Patterns, drivers, and challenges of vector-borne zoonotic disease emergence. Vector Borne Zoonotic Diseases. 

• Swei, A., O'Connor, K.E.†, Couper, L. †, Conrad, P., Padgett, K., Burns, J., Yoshimizu, M.H., Ben Mamoun, C., Lane, R., Kjemtrup, A. 2019. Evidence for transmission of the zoonotic apicomplexan parasite Babesia duncani. International Journal for Parasitology.  https://doi.org/10.1016/j.ijpara.2018.07.002

• O'Connor, K.E., Kjemtrup, A., Conrad, P., Swei, A. 2018. A highly sensitive, diagnostic protocol to detect the blood-borne pathogen, Babesia duncani. Journal of Parasitology. https://doi.org/10.1645/17-155

• ​Swei A, Bowie VC, Bowie RCK. 2015. Comparative genetic diversity of Lyme disease bacteria in Northern Californian ticks and their vertebrate hosts. Ticks and Tick-borne Diseases. 6: 414-23.

• Swei A, Russell BJ, Naccache SN, Kabre B, Veeraraghavan N, Pilgard, M.A., Johnson, B.J.B., Chiu, C.Y. 2013. The genome sequence of Lone Star Virus, a highly divergent bunyavirus found in the Amblyomma americanum tick. PLoS ONE 8(4): e62083. doi:10.1371/journal.pone.0062083

• Swei, A., J.J.L. Rowley, D. Rödder, M. L. L. Diesmos, A. C. Diesmos, C. J. Briggs, R. Brown, T. T. Cao, T. L. Cheng, R. A. Chong, B. Han, J.-M. Hero, H. D. Hoang, M. D. Kusrini, D. T. T. Le, J. A. McGuire, M. Meegaskumbura, M. S. Min, D. G. Mulcahy, T. Neang, S. Phimmachak, D.Q. Rao, N. M. Reeder, S. D. Schoville, N. Sivongxay, N. Srei, M. Stöck, B. L. Stuart, L. S. Torres, D. T. A. Tran, , T. S. Tunstall, D. Vieites, V. T. Vredenburg. Vredenburg. 2011. Is chytridiomycosis an emerging infectious disease in Asia? PLoS ONE 6(8): e23179.