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Dryad

Changes in transmission rates drive seasonal patterns of shrimp black gill disease

Abstract

Quantifying the processes affecting disease dynamics is critical for informing management strategies of fisheries. We present the results of a series of experiments and mechanistic models to disentangle the roles of transmission, mortality, and recovery in driving seasonal prevalence of shrimp Black Gill (sBG) disease in penaeid shrimp. We quantified seasonal sBG transmission to uninfected sentinel shrimp deployed into the environment. Next, we manipulated temperature and infection status in laboratory experiments to quantify drivers of host mortality and recovery. We then utilized these experiments to parameterize a series of mechanistic models to determine if disease dynamics were driven by host density-dependent or independent factors. Transmission was highest during the summer, with 75-91% of shrimp acquiring infection, but declined substantially in all other seasons (0-10% infection prevalence). In our lab experiments, we observed little disease-induced mortality and complete recovery from infection in all treatments. Our models revealed that host density did not drive disease dynamics. Together, this suggests that the seasonal change in sBG is due to high transmission rates in the summer months, followed by gradual recovery when transmission rates are low. Our methodology provides a framework to quantify drivers of seasonal variation in disease prevalence in fisheries.