THE ROLE OF RESERVOIR HOST COMMUNITIES IN THE MAINTENANCE OF White spot syndrome virus IN THE NORTHERN GULF OF MEXICO  

White spot syndrome virus (WSSV) is one of the most significant crustacean pathogens and a major impediment to the profitability of crustacean culture. WSSV is thought to have originated in southeast Asia and was first reported in the U.S. in coastal shrimp aquaculture facilities in Texas and South Carolina in 1995. The virus has persisted in U.S. coastal waters since 2005.  WSSV can infect almost any decapod crustacean and thus can exist in the environment in a variety of species. In the southern United States, where interest in the farming of a number of crustaceans, e.g., blue crabs (soft-shell shedding, and pond culture), white shrimp, spiny lobster (Panulirus argus), and freshwater prawns, is increasing, WSSV is likely to be a significant impediment to the growth of those industries just as it has been to the domestic crayfish industry. Therefore, identifying potential reservoir hosts among wild native crustacean species and understanding the transmission among those hosts and farmed hosts will be vitally important for managing the virus's impact on U.S. aquaculture.  

In surveys conducted in Mississippi and Louisiana from 2013 through 2015 we found WSSV in the blue crab (Callinectes sapidus) (8.3%, n=12), purple marsh crab (Sesarma reticulatum) (10.0%, n=20), Gulf mud fiddler crab (Uca longisignalis) (50.0%, n=72), panacea sand fiddler crab (U. panacea) (10.8%, n=1404), mudflat fiddler crab (U. rapax) (23.0%, n=88), spined fiddler crab (U. spinicarpa) (35.7%, n=98), red-jointed fiddler crab (U. minax) (22.7%, n=22), squareback marsh crab (Armasus cinereum) (26.7%, n=30), daggerblade grass shrimp (Palaemonetes pugio) (9.4%, n=1244), and Gulf white shrimp (Litopenaeus setiferus) (20.0%, n=40).  In controlled experiments, we observed 100% mortality rates in the commonly cultured L. vannamei and the three penaeid shrimp species native to the Gulf of Mexico: white shrimp, brown shrimp (Farfantepenaeus aztecus), and pink shrimp (Farfantepenaeus duorarum) after 2−5 days of being inoculated with WSSV. Similarly, we observed 100% mortality of blue crabs following injection exposure.  Mean time to death was 51.8 h.  

To elucidate the role of multi-species reservoir host communities in maintaining WSSV in the environment, we developed a metacommunity model comprising multiple species distributed among multiple spatially discontinuous habitat patches.  The model is matrix based and includes four compartments, Susceptible hosts, Infected living hosts, Free virus, and Dead infected hosts. The model indicates that maintenance of WSSV in reservoir hosts depends on the mean value of the important parameters contributing to the basic reproduction number, R₀. WSSV may be maintained in a region even though the R₀ is less than one for some of the species. WSSV will be maintained in those species by spill-over from those species with R₀s greater than unity.