Susceptibility of Shellfish Aquaculture Species in the Chesapeake Bay and Maryland Coastal Bays to the Ostreid Herpesvirus-1 Microvariants

Abstract

The Ostreid herpesvirus 1(OsHV-1) and its microvariants are highly virulent pathogens that cause mass mortalities of oysters and pose a threat to the shellfish aquaculture industry globally. OsHV-1 causes economically devastating mass mortality events up to 100% in the pacific oyster (Crassostrea gigas). However, OsHV-1 and its variants lack host specificity and are known to infect a range of bivalve species, such as bay scallops (Argopecten irradians), and be carried by the European green crab (Carcinus maenas). A recent laboratory study indicates that the eastern oyster (Crassostrea virginica) can experience infection and mortality from OsHV-1 which has significant implications for aquaculture species used in Maryland and globally, as eastern oysters have a wide geographic range spanning Northwest Atlantic to Panama and Venezuela. Therefore, determining the susceptibility of economically and ecologically important United States bivalve species to OsHV-1 is an essential step in improving biosecurity and disease management to protect the sustainability of the aquaculture industry. There is a lack of monitoring and research on OsHV-1 on the East coast of the United States, including in eastern oysters grown in the Chesapeake Bay, Virginia, and Maryland Coastal Bays where aquaculture is an important industry for food production, job security, and restoration efforts. Chesapeake and Maryland Coastal Bay species are already threatened by various parasitic and viral diseases, indicating that they may be vulnerable to OsHV-1. Surveys were conducted in June-August 2021 in the Maryland portion of the Chesapeake Bay to determine the prevalence and viral load of OsHV-1 at five aquaculture farms. Using quantitative PCR, OsHV-1 was not detected at any sites. However, continuous surveillance is crucial in mitigating possible introductions to the area. Experiments conducted at the University of Arizona examined the susceptibility and horizontal transmission of eastern oysters and hard clams. Importantly, it has been shown that OsHV-1 microvariants did not cause mortality or infection in eastern oysters and hard clams through natural infection pathways. However, eastern oysters, when injected with OsHV-1, can transmit the virus. This creates implications for same or similar species cultivated throughout the East Coast and Gulf of Mexico Coasts as well as transport of bivalves to the West Coast. Further experimentation using various family lines and establishment of surveillance programs is necessary to fully manage the spread and impact of OsHV-1 related disease.