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Animal and Plant Health Inspection Service
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Frequently Asked Questions: Infection by ostreid herpesvirus-1 (OsHV-1) microvariants, sometimes referred to as Pacific Oyster Mortality Syndrome (POMS)

  1. What is ostreid herpesvirus-1 (OsHV-1)?
    Infection with ostreid herpesvirus-1 (OsHV-1) microvariants have been reported in several bivalve species. The term “microvariant” refers to closely related variants of ostreid herpesvirus-1 (OsHV-1), which have caused mass mortalities of oysters in Europe, the United States, Asia, Australia, and New Zealand. Infection is often lethal for Pacific oyster (Crassostrea gigas) spat and juveniles. Affected animals show decreased feeding and swimming activities, as well as sudden death; however, infection can also occur with no signs of disease. OsHV-1 is not transmissible to humans (i.e., not zoonotic).

  2. What species of shellfish are affected by ostreid herpesvirus 1 (OsHV-1) microvariants?
    The primary species susceptible to mortality from OsHV-1 microvariants are the Pacific oyster (Crassostrea gigas) and the Portuguese cupped oyster (Crassostrea angulate); however, research on species susceptibility is ongoing. For example, literature suggests that additional mollusk species may be susceptible to infection.

  3. How are ostreid herpesvirus 1 (OsHV-1) microvariants transmitted? Is it possible to introduce this virus from shells obtained through shell recycling programs?
    OsHV-1 microvariants are known to spread between populations and animals through the movement of animals, shells, and water, and presumably also equipment, packaging, or gear that has not been cleaned and disinfected. The virus may be carried in live or frozen shellfish. It is unclear whether OsHV-1 microvariants can also transmit vertically from parents to offspring. It is recommended that thorough drying of shells should be used to kill residual virus.

  4. Which agency has authority over animal pathogens/diseases that could be introduced via live animal imports from foreign waters/ countries?
    Under the Animal Health Protection Act (AHPA) the U.S. Secretary of Agriculture has the authority over the prevention, detection, control, and eradication of animal diseases, including aquaculture; with animal defined as any member of the animal kingdom (excluding humans). Section 10401 (7USC) provides the authority for the U.S. Secretary of Agriculture to regulate aquaculture. This includes the regulation of imported aquatic animals and products, diagnostic services, and disease control and eradication. Additional Federal regulations make it illegal to place imported shellfish, water, or other foreign materials in U.S. waters.

  5. How is the introduction of ostreid herpesvirus 1 (OsHV-1) microvariants prevented through the importation of live oysters intended for human consumption?
    The potential introduction of OsHV-1 occurs through contact of imported oysters (including their shells and transport water) with U.S. oysters or their environment. Currently, there are no Federal import regulations to prevent the introduction of OsHV-1 microvariants via live animal imports, so it is recommended that importers take specific precautions bringing live oysters into the United States from countries where OsHV-1 microvariants have been detected; principally do not place oysters in U.S. waters for freshening (wet storage) or other purposes, do not discharge untreated water used to clean shipping materials or hold oysters in the environment or U.S. waters, and do not discard oyster remnants or shells into the environment or U.S. waters.

  6. Is it possible that oysters may enter the U.S. from countries known to have ostreid herpesvirus 1 (OsHV-1) microvariants?
    Currently, the U.S. Department of Agriculture does not have any Federal requirements prohibiting live oyster imports from countries where OsHV-1 microvariants have been detected. Some States may have import controls for OsHV-1.

  7. How is the U.S. Department of Agriculture addressing the potential risk of ostreid herpesvirus 1 (OsHV-1) microvariants introduction into the U.S., including potential impacts from the outcome of the FDA’s equivalence determination regarding raw molluscan shellfish imported from certain EU Member States?
    In 2020, the U.S. Food and Drug Administration and the European Commission finalized equivalence determinations of each other’s system of food safety control measures for raw molluscan shellfish. These equivalence determinations initially will enable exports of shellfish from Massachusetts and Washington to the EU and imports from Spain and the Netherlands to the United States. Negotiations concluded in 2022 and publication by the European Commission of the export health certificate that will be issued by the National Oceanic and Atmospheric Administration (NOAA) signaled the bilateral start of trade, scheduled for February 27, 2022.
    The U.S. Department of Agriculture evaluated the potential risks that imported shellfish may introduce OsHV-1 microvariants into U.S. domestic and wild shellfish populations, and has posted the review at Potential Introduction Pathways of Ostreid Herpesvirus-1 (OsHV-1) in the United States.

  8. Who should be contacted if ostreid herpesvirus 1 (OsHV-1) microvariants are suspected or detected?
    Contact your State Animal Health Official and/or the USDA APHIS Area Office.

  9. Where can I find more information on ostreid herpesvirus 1 (OsHV-1) microvariants?
    More information is available under “Mollusk Diseases” on the USDA APHIS website Aquatic Animal Diseases.

  10. Where can I find more information on the international movement of oysters and associated resources?
    In addition to the U.S. Department of Agriculture (USDA), there are several Federal agencies involved in efforts to protect oyster sectors in the U.S. including the U.S. Food and Drug Administration (FDA), the National Oceanic and Atmospheric Administration (NOAA), and the U.S. Environmental Protection Agency (EPA). More information and free tags for dealers importing foreign shellfish are available from the East Coast Shellfish Growers Association.
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