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Jerri Bartholomew in front of shrubbery

Jerri L. Bartholomew

Director, J.L. Fryer Aquatic Animal Health Laboratory
Department of Microbiology

Jerri L. Bartholomew

Director, J.L. Fryer Aquatic Animal Health Laboratory
Department of Microbiology


Our research focuses on the pathogens that affect the health of wild Pacific salmon populations, particularly myxozoan parasites, which have a complex life cycle, requiring both a fish and annelid host.

Disease Effects on Wild Populations

The myxozoan Ceratonova shasta is endemic across the Pacific NW and causes high mortality in juvenile salmon in some river systems. A long-term project in the Klamath River integrates monitoring and research to develop recommendations for fishery management by providing real time data on parasite densities and their predicted effects on juvenile salmon, and by linking areas of high disease risk with physical parameters such as water flows and temperature. We are applying similar approaches to the Deschutes River. Research in the Willamette River further investigates C. shasta dynamics in this system as well as conducting surveys for parasites of native and introduced fishes.

Interactions Between Hatchery and Wild Fish

Research being conducted in the Willamette River basin investigates pathogen transmission between hatchery populations and naturally reproducing populations. We are also looking at the effects of multiple infections on salmon survival.

Climate Change Effects on Disease

Climate change is expected to have profound effects on host-pathogen interactions. We are examining how this might affect myxozoan disease by developing predictions for how the phenology of parasite life cycles will change under future climates, how changing flow dynamics will alter disease, and to identify river habitats that should be protected as refugia.

Parasite Evolution and Diversity

Myxozoans not only have complex life histories, but enigmatic relationships as revealed by molecular sequence analysis. Continued investigations into the genetics of C. shasta have revealed that it is actually a parasite complex, with different strains specifically evolving with different salmonid hosts. This finding has caused us to rethink assumptions about host-parasite interactions. We are currently involved in genome sequencing and transcriptomic studies that will aid us in developing better diagnostic tools as well as to answer questions about basic parasite biology and phylogenetic relationships.

Parasite Invasion

The first step in Myxozoan infection is activation of their polar capsules. These specialized cells resemble the nematocysts of their cnidarian relatives and could offer possibilities for development of therapeutants. We are working with Israeli scientists to understand the physical process and the genes that control it, as well as to test candidate treatments that affect the process.

Evolution of the Immune System and Role of Mucosal Immunity

This salmonid-C. shasta relationship has proved an ideal model for investigating mucosal immunity in a primitive host and is the basis for a collaboration with Oriol Sunyer, University of Pennsylvania, funded by the National Science Foundation and National Institutes of Health.

Research Interests

  • Salmon Diseases
  • Myxozoan Parasites
  • Host Resistance Mechanisms
  • Parasite Evolution



Ph.D., Oregon State University


  • Americus, B., Hams, N., Klompen, A.M.L., Alama-Bermejo, G., Lotan, T., Bartholomew, J.L., and Atkinson, S.D. Accepted September 2021. The cnidarian parasite Ceratonova shasta utilizs inherited and recruited venom-like compounds during infection. PeerJ.
  • Brekhman, V., Ofek-Lalzar, M., Atkinson, S.D., Alama-Bermejo, G., Maor-Landaw, K., Malik, A., Bartholomew, J.L., and Lotan, T. 2021. Proteomic analysis of the parasitic Cnidarian Ceratonova shasta (Cnidaria: Myxozoa) reveals diverse roles of actin in motility and spore formation. Front. in Mar. Sci. 8:632700.
  • Kumar, G., Ertl, R., Nilsen, F., Bartholomew, J.L., and El-Matbouli, M. 2021. Data of de novo transcriptome assembly of the myxozoan parasite Tetracapsuloides bryosalmonae. Data Brief 35:106831.
  • Barrett, D.E. and Bartholomew, J.L. 2021. A tale of two fish: Comparative transcriptomics of resistant and susceptible steelhead following exposure to Ceratonova shasta highlights differences in parasite recognition. PLoS One. 16(2):e0234837.
  • Americus, B., Schisler, G.J., Bartholomew, J.L., and Atkinson, S.D. 2021. Myxobolus cerebralis Causes Presporogonic Mortality in Juvenile Mountain Whitefish. J. of Aquatic Animal Hlth. 33(2):116-122.
  • Bartošová-Sojková, P., Kyslík, J., Alama-Bermejo, G., Hartigan, A., Atkinson, S.D., Bartholomew, J.L., Picard-Sánchez, A., Palenzuela, O., Faber, M.N., Holland, J.W., and Holzer, A.S. 2021. Evolutionary Analysis of Cystatins of Early-Emerging Metazoans Reveals a Novel Subtype in Parasitic Cnidarians. Biology 10(2):110.
  • Americus, B., Bartholomew, J.L., Lotan, T., and Atkinson, S.D. 2020. A comparison of the structure and function of nematocysts in free-living and parasitic cnidarians (Myxozoa). International Journal for Parasitology, 50: 763-769. DOI:10.1016/j.ijpara.2020.04.012
  • Americus, B., Austin, B., Lotan, T., Bartholomew, J., and Atkinson, S. 2020. In vitro and in vivo assays reveal that cations affect nematocyst discharge in Myxobolus cerebralis (Cnidaria: Myxozoa). Parasitology, 147(12):1352-1358. DOI:10.1017/S0031182020001158
  • Kyger, R., Luzuriaga, A., Peri, S., Layman, T., Sandberg, T.O.M., Singh, D., Atkinson, S.D., Bartholomew, J.L., Huchon, D., Soojin, V., and Alvarez-Ponce, D. 2020. Myxosporea (Myxozoa, Cnidaria) lack DNA cytosine methylation. Molecular Biology and Evolution, msaa214. DOI:10.1093/molbev/msaa214
  • Tilic, E., Atkinson, S.D., Rouse, G. 2020. Mitochondrial genome of the freshwater annelid Manayunkia occidentalis Mitochondrial DNA Part B: Resources, 5(3): 3313-3315. DOI:10.1080/23802359.2020.1815604
  • Alama-Bermejo, G,, Meyer, E., Atkinson, S.D., Holzer, A.S., Wiśniewska, M.W., Kolísko, M., and Bartholomew, J.L. 2020. Transcriptome-wide comparisons and virulence gene polymorphisms of host-associated genotypes of the cnidarian parasite Ceratonova shasta in salmonids. Genome Biology and Evolution, 12(8), 1258-1276. DOI:10.1093/gbe/evaa109
  • Taggart-Murphy, L., Alama-Bermejo, G., Dolan, B., Takizawa, F., and Bartholomew, J. 2020. Differences in inflammatory responses of rainbow trout infected by two genotypes of the myxozoan parasite Ceratonova shasta. Dev Comp Immunol. Aug 23;114:103829. doi: 10.1016/j.dci.2020.103829.
  • Kumar, G., Ertl, R., Bartholomew, J.L., and El-Matbouli, M. 2020. Transcriptome Analysis Elucidates the Key Responses of Bryozoan Fredericella sultana during the Development of Tetracapsuloides bryosalmonae (Myxozoa). Int J Mol Sci. Aug 17;21(16):5910. doi: 10.3390/ijms21165910.
  • Yahalomi, D., Atkinson, S.D., Neuhof, M., Chang. E., Philippe, H., Cartwright, P., Bartholomew, J.L., and Huchon, D. 2020. A cinidarian parasite of salmon (Myxozoa: Henneguya) lacks a mitochondrial genome. Proc Natl Acad Sci U S A. 2020 Mar 10;117(10):5358-5363. doi: 10.1073/pnas.1909907117. Epub 2020 Feb 24. PMID: 32094163
  • Richey, C.A., Kenelty, K.V., Hopkins, K.V.S., Stevens, B.N., Martinez-López, B., Hallett, S.L., Atkinson, S.D., Bartholomew, J.L., and Soto, E. 2020. Validation of environmental DNA sampling for determination of Ceratonova shasta (Cnidaria: Myxozoa) distribution in Plumas National Forest, CA. Parasitol. Res. PMID: 31897785.