Oyster herpes
Latest symptom of global warming:
Rachel Kaufman
Don't worry, oyster herpes isn't a new side effect of eating "the
food of love."
The incurable, deadly virus is, however, alarming fishing communities
in Europe, where oyster herpes seems to be spreading, and could go on
spreading as seas continue to warm, experts say.
Male and female oysters release sperm and eggs into water (file
photo). Photograph by Robert Sisson, National Geographic |
In July lab testing of farmed oysters detected the first known United
Kingdom cases of herpes in the shellfish. The virus has already killed
between 20 to 100 percent of breeding Pacific oysters in some French
beds in 2008, 2009, and 2010, according to the French Research Institute
for Exploitation of the Sea (Ifremer).
The reason for oyster herpes's emergence in Pacific oysters off
England remains a mystery, though global warming may have played a part,
experts speculate.
A new strain named Ostreid herpesvirus 1 (OsHV-1) ?var (mew-var), the
virus remains dormant until water temperatures exceed 16 C (61 degrees
F), which UK waters reach in the height of summer, according to Kevin
Denham of the British Government's Fish Health Inspectorate.
With that in mind, Director of Ifremer's genetic and pathology lab
Tristan Renault, said that global warming "could be an explanation of
the appearance of this particular type of the virus."
Though all herpes strains are DNA-based viruses, herpes, which
infects everything from cows to clams to monkeys, comes in a wide
variety of species, each with their own unique set of symptoms. Among
humans, perhaps the best known forms are the Herpes simplex viruses,
which are spread through close contact and can manifest themselves as
oral and genital blisters.
Ostreid herpes viruses are known to affect not only oysters but also
clams, scallops, and other mollusks, according to Renault.
The new oyster herpes
Herpes-infected shellfish aren't new to science, but in 2008, the
first year a huge increase in mortality rates was detected in France,
Ifremer detected a new variation of the virus.
Like the other strains of herpes that affect mollusks, OsHV-1 ?var
attacks young oysters during breeding season, when the mollusks' bodies
are so focused on producing sperm and eggs that the oysters have no
energy to maintain an immune system, Renault said.
But OsHV-1 ?var is "more virulent than strains we identified before,"
Renault said, adding that the virus is so efficient at killing its hosts
that it can wipe out 80 percent of the oysters in a bed within a week.
That death rate is the only outward sign something's wrong, he added,
because a oyster herpes have no visible symptoms, and diagnosis is
possible only through lab testing.
Oyster herpes appears in Britain
Though oyster herpes can't be transmitted to humans, it does threaten
the fishing industry, since dead oysters are unsafe for eating, and
that's exactly what worries oyster harvesters such as Seasalter
Shellfish.
Based in the southeastern English city of Whitstable, where oysters
have been harvested for centuries, Seasalter this summer became the
first company to discover the herpes-ravaged oysters in the UK.
The finding prompted an investigation by the Fish Health
Inspectorate, which detected the virus and learned that Seasalter had
employed equipment previously used in France to refurbish oyster beds.
"We were told it had been out of the water for a number of years,"
Denham said. "Nevertheless there's still a possibility" that the virus
could have traveled from infected French beds via the gear. Possible
culprits also include other reused equipment or water transferred from
an infected area.
Could oyster herpes spread
To keep the UK oyster-herpes outbreak from spreading, the British
Government has banned the shipping of oysters out of affected areas,
most of which, like Whitstable, are around the mouth of the River Thames
in southeastern England.
No matter what measures are taken, Denham said, oyster herpes is
going to be tough to kick. Even if all the infected Pacific oysters are
removed from oyster farms, wild Pacific oysters will still be present in
surrounding waters, perhaps acting as "a reservoir for infection."
It's unlikely, though, that OsHV-1 ?var would end up in US oyster
beds, Renault said, because the United States doesn't typically import
oysters from Europe.
But a less virulent, herpes-like virus has been detected in farmed
oysters off California. If sea temperatures continue to rise, he said,
perhaps ?var or something like it could emerge in US waters too.
National Geographic News |