Population Density of the Northern Sea Otter (Enhydra lutris kenyoni) as an Indicator of Strep Syndrome Transmission Mechanism Open Access

Withers, Megan (Spring 2019)

Permanent URL: https://etd.library.emory.edu/concern/etds/n009w333j?locale=en


The Northern sea otter (Enhydra lutris kenyoni) in Alaska, U.S. has recently experienced unusual mortality events due to Strep syndrome caused primarily by Streptococcus infantarius, Streptococcus bovis, and Streptococcus phocae. The pathogenicity and transmission method of this disease is currently unknown, making it difficult to predict the disease’s prevalence and the risk it poses to the species. Preliminary evidence from higher-density populations that have experienced significant mortality suggest that population density may affect transmission. To test this hypothesis, we acquired stranding data from the U.S. Fish and Wildlife Service (FWS), partitioned the population into discrete ranges using QGIS, and calculated the percentage of infected individuals in these areas from 2001 to 2014. Using abundance data from USFWS and the United States Geological Survey (USGS), among other sources, we calculated population density for these regions over time. We then tested the relationship between infection and population density using generalized linear models and generalized linear mixed models. Additional variables considered were infected individuals’ age, sex, and body condition. These variables were included to clarify which individuals may be at greatest risk for infection as demographic details have been inconsistent in previous literature. Additionally, we determined the primary physical locations for bacterial infection. Previous literature has noted a high percentage of bacteria in the intestines and we sought to confirm this finding to elucidate the physical characteristics of infection. Results indicate that population density does not significantly influence Strep prevalence, but that males are at greater risk for the disease. These results suggest that Strep may be transmitted in a frequency-dependent manner and influenced by behavior disparities between the sexes. Additionally, the relative frequency at which certain tissues, such as the spleen, test positively for streptococci bacteria contradicts previous literature regarding bacterial presence in the intestines. Therefore, the survival and transport of streptococci bacteria by macrophages requires additional research, as does the proposal of infection via the intestines. Overall, these findings can be used to guide federal agencies in research prioritization and management.

Table of Contents

Introduction - 1

Methods - 6

Results - 18

Discussion - 24

Works Cited - 29

Appendix - 41

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