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

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.