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Detection of norwalk-like virus in shellfish implicated in illness
Y Shieh1, S S Monroe, R L Fankhauser
1USFDA Gulf Coast Seafood Laboratory, Dauphin Island, AL 36528, USA. yshieh@cfsan.fda.gov.
Abstract:
In the 1990s, Norwalk-like viruses (NLVs) were identified in patient specimens as the primary pathogen associated with shellfish-borne gastroenteritis in the United States. Identification of these viruses from implicated shellfish has been difficult due to inefficient recovery of viruses, natural polymerase chain reaction (PCR) inhibitors in shellfish, and low virus contamination. Recent improvements to the method of detecting NLVs in shellfish include enhanced processing of virus and shellfish samples, application of nested PCR and nucleotide sequencing, and increased knowledge of NLV genetic diversity. Using a newly developed and sensitive method, an NLV G2 strain was identified in 2 oyster samples implicated in a 1998 California outbreak involving 171 cases. NLV capsid primers demonstrated a greater specificity of PCR detection than did polymerase primers. The 175-base viral capsid nucleotide sequences derived from oysters were 100% identical to those derived from a patient stool sample. This finding supports the epidemiologic associations indicating that contaminated shellfish serve as the vehicle for NLV transmission.
Insights
Norwalk-like viruses (NLVs) cause shellfish-borne gastroenteritis. A new sensitive method detected NLV G2 in oysters linked to a 1998 California outbreak, confirming shellfish as a transmission vehicle.
Area of Science:
- Foodborne illness
- Virology
- Molecular biology
Background:
- Norwalk-like viruses (NLVs) are a major cause of shellfish-borne gastroenteritis in the U.S.
- Detecting NLVs in shellfish is challenging due to low contamination and inhibitors.
- Previous methods for NLV detection in shellfish were inefficient.
Purpose of the Study:
- To develop and apply a sensitive method for detecting NLVs in shellfish.
- To identify the specific NLV strain involved in a 1998 California outbreak.
- To confirm the role of contaminated shellfish in NLV transmission.
Main Methods:
- Enhanced processing of virus and shellfish samples.
- Application of nested polymerase chain reaction (PCR) and nucleotide sequencing.
- Use of NLV capsid primers for enhanced PCR detection specificity.
Main Results:
- A novel NLV G2 strain was identified in two oyster samples.
- The outbreak involved 171 cases in California in 1998.
- Sequences from oysters were 100% identical to those from a patient stool sample.
Conclusions:
- The newly developed method is sensitive for detecting NLVs in shellfish.
- Contaminated shellfish were confirmed as the vehicle for NLV transmission in this outbreak.
- NLV capsid primers offer superior specificity for PCR detection compared to polymerase primers.