From Virus Research:

"Herpes and herpes-like viruses are known to infect a wide range of bivalve mollusk species throughout the world," according to coauthor Tristan Renault and his colleagues. Renault is the director of the French Research Institute for Exploration of the Sea.

He and his team note that "abnormal summer mortalities" associated with the new herpes virus Ostreid herpesvirus 1 (OsHV-1) have been reported among the Pacific cupped Crassostrea gigas, an oyster important to worldwide commercial harvests. For example, this type of oyster is the number one shellfish resource for the state of Washington.

In a prior study, these scientists demonstrated how quickly this new particular strain of herpes reproduces within oysters. It attacks young oysters at times when their immune systems are compromised.

Renault told National Geographic that global warming "could be an explanation of the appearance of this particular type of the virus." Kevin Denham of Britain's Fish Health Inspectorate explained that the virus remains dormant until water temperatures exceed 61 degrees Fahrenheit. And that has been happening a lot this summer.

The Cause

The herpes virus is also thought to infect clams, scallops, and other mollusks.  This strain of herpes that attacks mollusks is not the herpes simplex that infects humans. Further, there is no evidence whether the herpes in mollusks can infect humans but many oysters are eaten raw and this means that the oysters are ingested with the living oyster herpes virus. Could this virus affect humans as well? No one really knows.

There is evidence that global warming is a factor but there are many things that are weakening immune systems of marine species including increasing levels of acidity in the seas, chemical pollution, and diminishment of biodiversity.

One thing’s for sure, herpes certainly does affect oysters and they are dying, and that is a tragedy far more serious than cold sores and occasional outbreaks in humans.