OYSTER HERPESVIRUS - ENGLAND, IRELAND: EMERGING, OIE
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[1] Background
[2] UK (England), OIE immediate notification [3] UK (England), OIE follow-up report 2 [4] UK (England), OIE follow-up report 3 [5] Ireland, OIE immediate notification
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[1] Background
Date: 6 Aug 2010
Source: National Geographic Daily News [Abridged, edited] <http://news.nationalgeographic.com/news/2010/08/100806-oyster-herpes-global-warming-climate-change-science/>
Oyster Herpes: Latest Symptom of Global Warming?
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In July [2010] lab testing of farmed oysters detected the 1st 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) (mew-var)_, the virus remains dormant until water temperatures exceed 16 C [61 degrees F], which U.K. waters reach in the height of summer, according to Kevin Denham of the British government's Fish Health Inspectorate. With that in mind, Tristan Renault, director of Ifremer's genetic and pathology lab, 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. Herpes-infected shellfish aren't new to science, but in 2008—the 1st 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 (mew-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 (mew-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.
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 1st company to discover the herpes-ravaged oysters in the U.K.
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.
To keep the U.K. 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 (mew-var) would end up in U.S. 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 (mew-var) or something like it could emerge in U.S. waters too.
[Byline: Rachel Kaufman]
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[2] UK (England), immediate notification
Date: 21 Jul 2010
Source: OIE immediate notification [abridged, edited] <http://www.oie.int/wahis/public.php?page=single_report&pop=1&reportid=9527>
Oyster herpesvirus (OsHV-1, (mew-var)), United Kingdom
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Information received on 21 Jul 2010 from Dr Nigel Gibbens, Chief Veterinary Officer, Department for Environment, Food and Rural Affairs, Department for Environment, Food and Rural Affairs, London, United Kingdom
Summary
Report type: Immediate notification
Start date: 12 Jul 2010
Date of 1st confirmation of the event: 16 Jul 2010 Report date: 21 Jul 2010 Date submitted to OIE: 21 Jul 2010 Reason for notification: Emerging disease
Morbidity:: 60 percent
Mortality: 60 percent
Zoonotic impact: No
Causal agent: OsHV-1, [mew-var]
New outbreaks
Outbreak 1: Seasalter Foreshore, Whitstable Harbour, Whitstable Harbour, Kent, England Date of start of the outbreak: 12 Jul 2010 Outbreak status: Continuing Epidemiological unit: Farm Water type: Salt water Population type: Farmed Production system: Open Affected animals Species/ Morbidity/ Mortality/ Susceptible/ Cases/ Deaths/ Destroyed/ Slaughtered Pacific Oyster (_Crassostrea gigas_)/ 100 percent/ 100 percent/ 9 000 000/ 9 000 000/ 9 000 000/ 0/ 0 Affected Population: Farmed population of _Crassostrea gigas_ (diploid and triploid), grown on beds and trestles. All stages affected from spat to adult.
Epidemiological comments:
Movement controls in the form of a confirmed designation have been applied to the Oyster herpesvirus Containment Area known as "Compartment 6 - Swale, Thames and North Kent Coast".
Under the current conditions of the designation, movements of _Crassostrea gigas_ are permitted only for direct human consumption, subject to hygiene regulations.
In addition, the controls stipulate that disposal of dead Pacific oysters Crassostrea gigas of all stages must be by an approved method for disposal of Category 2 animal-by-product waste.
Epidemiological investigations are underway.
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[3] UK (England), OIE follow-up report 2
Date: 6 Aug 2010
Source: OIE, Follow-up report No 2 [abridged, edited] <http://www.oie.int/wahis/public.php?page=single_report&pop=1&reportid=9583>
Oyster herpesvirus (OsHV-1, (mew-var)), United Kingdom
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Epidemiological comments:
Kent outbreak
1. Update as of 29 July 2010
Since the initial outbreak further samples have been collected from the other Crassostrea gigas farms in the containment area and from a wild population of this species. At present, there are no indications that the virus has spread to other stocks within the containment area and no further mortalities have been reported, although not all tests have been completed to date. We have been notified of 2 sites that received _C. gigas_ from the affected farm earlier this year and prior to the outbreak. To date, neither site has reported mortalities or stock problems; however, arrangements are in place to test both sites.
An initial epidemiological study and report has been produced; there is no evidence of spread from the area, but a number of possible routes that the virus may have entered the positive site have been identified, although none has been confirmed as the route of infection. The epidemiological investigation is continuing.
The surveillance programme for OsHV-1 (mew-var) in the rest of the United Kingdom is continuing; to date, no further reports of abnormal mortality have been received and no other positive results have been recorded.
2. Update as of 5 August 2010
Since the previous follow-up report, there are no changes to the epidemiological situation except that the mortality on the 1st affected site appears to have peaked with stock loss reported to have reached 100 percent in some stocks on site. To date, there have been no other reported mortalities or stock problems within or outside the OsHV containment area and the surveillance programme for OsHV-1 (mew-var) in the rest of the United Kingdom is continuing.
Of the 3 additional samples collected from other -C. gigas- sites within the containment area post-outbreak, one has been confirmed as negative; results are still pending for the other
2 samples. Contact testing is underway for the 2 sites that received -C. gigas- from the affected farm earlier this year.
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[4] UK (England), OIE follow-up report 3
Date: 13 Aug 2010
Source: OIE Follow-up report No 3 [Abridged, edited] <http://www.oie.int/wahis/public.php?page=single_report&pop=1&reportid=9602>
Oyster herpesvirus (OsHV-1, (mew-var)), United Kingdom
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Epidemiological comments:
Update as of 12 Aug 2010
Kent outbreak:
The mortality event at the affected site is now reported as having passed, and the 1st of the 2 consecutive inspections required by Article 4 of Commission Regulation (EU) 175/2010 is scheduled to be carried out today, this is approximately one month after the initial report of the abnormal mortality.
Contact chasing of the 2 sites that had purchased stock from within the Containment Area prior to the identification of the infection is now complete as are the tests for the 3 additional samples collected within the containment area, and all samples have tested negative by PCR.
There is therefore no evidence for the spread of infection from the actual site that experienced the mortality.
The surveillance programme for the rest of the coast of England and Wales is continuing, and to date no further positive results for OsHV-1 have occurred.
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[5] Ireland, OIE immediate notification
Date: Mon 16 Aug 2010
Source: OIE Immediate notification [abridged, edited] <http://www.oie.int/wahis/public.php?page=single_report&pop=1&reportid=9577>
Suspected Ostreid herpes virus 1 (OsHV1), Ireland
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Information received on 16 Aug 2010 from Mr Patrick J. Rogan, Chief Veterinary Officer, Agriculture House, Department of Agriculture and Food, Dublin, Ireland
Summary
Report type: Immediate notification
Start date: 28 May 2010
Date of 1st confirmation of the event: 03 Jun 2010 Report date 16 Aug 2010 Date submitted to OIE: 16 Aug 2010 Reason for notification: Emerging disease
Morbidity: 3 scale05
Mortality: 3 scale05
Zoonotic impact: No
Causal agent: OsHV1 [mew-var]
Summary of outbreaks:
Total outbreaks: 14
Total animals affected
Species: Pacific oyster (_Crassostrea gigas_)
Epidemiological comments
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Mortalities have been considerable, particularly in seed. Half grown and adult oysters have also suffered mortalities in some areas though at lower levels. Transmission from site to site as well as through the water is believed to be occurring but the presence of the virus in all of these areas last year [2009] and the possibility of latency makes it impossible to be sure whether the source is introduction of stock from an infected area or as a result of latent infections in existing populations.
Although mortalities now appear to be at an end, reinfection of stocks which will be introduced between now and next summer [2011] is anticipated once the temperatures begin to climb again in June.
Between 3 June 2010 and 5 August 2010 OsHV1
(mew-Var) strain detected in all 14 bays using PCR and histopathology.
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[While in England one location, in Kent, has been reportedly affected, the emerging virus seems to have widely spread in Ireland, reported from the southern, western and northern coasts (see map at the above URL).
This agent is not (yet) included among OIE's listed aquatic diseases; at present notified and handled as an emerging disease.
Further reading:
Amelie Segarra, Jean Francois Pepin, Isabelle Arzul, Benjamin Morga, Nicole Faury and Tristan Renault (2010). Detection and description of a particular Ostreid herpesvirus 1 genotype associated with massive mortality outbreaks of Pacific oysters, _Crassostrea giga_ in France in 2008. Article in press, Virus Research (VIRUS-95207), 8 pages. - Mod.AS]
[see also:
2009
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Undiagnosed die-off, oysters - France: RFI 20090801.2697] ....................arn/ejp/dk
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