Geology topics

Oliver C. Kwok

Publications and source records attributed to Oliver C. Kwok.

3 recordsLinked to original sources

USGS2024

Increased pathogen exposure of a marine apex predator over three decades

Environmental changes associated with global warming create new opportunities for pathogen and parasite transmission in Arctic wildlife. As an apex predator ranging over large, remote areas, changes in pathogens and parasites in polar bears are a useful indicator of changing transmission dynamics in Arctic ecosystems. We examined prevalence and risk factors associated with exposure to parasites and viral and bacterial pathogens in Chukchi Sea polar bears. Serum antibodies to six pathogens were detected and prevalence increased between 1987–1994 and 2008–2017 for five: Toxoplasma gondii , Neospora caninum , Francisella tularensis , Brucella abortus/suis , and canine distemper virus. Although bears have increased summer land use, this behavior was not associated with increased exposure. Higher prevalence of F. tularensis , C. burnetii , and B. abortus/suis antibodies in females compared to males, however, could be associated with terrestrial denning. Exposure was related to diet for several pathogens indicating increased exposure in the food web. Elevated white blood cell counts suggest a possible immune response to some pathogens. Given that polar bears face multiple stressors in association with climate change and are a subsistence food, further work is warranted to screen for signs of disease.

Alaska↗

USGS2018

An update on Toxoplasma gondii infections in northern sea otters (Enhydra lutris kenyoni) from Washington State, USA

Toxoplasmosis in marine mammals is epidemiologically and clinically important. Toxoplasma gondii antibodies (by modified agglutination test, cut-off ≥1:25) were detected in serum of 65 of 70 (92.9%) northern sea otters ( Enhydra lutris kenyoni ) from Washington State, USA. Brains and/or muscles of 44 sea otters were bioassayed in mice (INF-γ knock-out [KO], Swiss Webster outbred [SW]) and viable T. gondii was isolated from 22 of 44 (50%); T. gondii strains were lethal to KO mice but not SW mice. These T. gondii isolates were further propagated in cell culture. Multi-locus PCR-RFLP genotyping of cell culture-derived tachyzoites revealed four different genotypes among 22 isolates including ToxoDB PCR-RFLP genotype #5 (14 isolates), #1 (three isolates), #3 (four isolates), and #167 (one isolate). PCR-DNA sequencing based genotyping using polymorphic gene GRA6 revealed one of four different alleles. Among the 14 RFLP genotype #5 strains, 10 have GRA6 sequences that match with the Type A, one match with the Type X, two strains did not generate sequence data, and one strain had double peaks at known polymorphic sites indicating a mixed infection. The seven strains belong to genotypes #1 and #3, all have identical sequences to T. gondii Type II reference isolate ME49. Genotype #167 strain has identical sequence to Type I reference strain. In summary, we observed high seroprevalence, and high rate of isolation of T. gondii from northern sea otters and predominant genotype #5 that has been previously reported a dominant and widespread strain among terrestrial wildlife in North America. GRA6 sequence analysis of the genotype #5 isolates indicated the dominance of Type A lineage in sea otters in Washington State.

Washington↗

USGS2016

Toxoplasma gondii antibody prevalence and two new genotypes of the parasite in endangered Hawaiian Geese (nene: Branta sandvicensis )

Toxoplasma gondii is a protozoan parasite transmitted by domestic cats ( Felis catus ) that has historically caused mortality in native Hawaiian birds. To estimate how widespread exposure to the parasite is in nene (Hawaiian Geese, Branta sandvicensis ), we did a serologic survey for T. gondii antibody and genetically characterized parasite DNA from the tissues of dead birds that had confirmed infections by immunohistochemistry. Of 94 geese sampled, prevalence on the island of Kauai, Maui, and Molokai was 21% ( n =42), 23% ( n =31), and 48% ( n =21), respectively. Two new T. gondii genotypes were identified by PCR-restriction fragment length polymorphism from four geese, and these appeared segregated geographically. Exposure to T. gondii in wild nene is widespread and, while the parasite is not a major cause of death, it could have sublethal or behavioral effects. How to translate such information to implement effective ways to manage feral cats in Hawaii poses challenges.

Hawai'i↗