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Detection of Antibodies Directed Towards Powassan Virus by PRNT

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Requisition Forms

Reference Details

Description:

Serological detection of neutralizing antibodies directed towards Powassan (POW) virus by Plaque Reduction Neutralization Test (PRNT).

Test Category:
Serology
Pathogen:
Powassan virus
Laboratory:
Viral Zoonoses
Illnesses and Diseases:
  • Powassan encephalitis
Specimen:

Serum. Minimum volume of 250ml required.

Collection Method:

Collect blood in serum separator tubes.

Specimen Processing, Storage and Shipping:
Store samples refrigerated or frozen until shipped for testing. Ship frozen samples on dry ice, and refrigerated samples on wet ice
Transportation of Dangerous Goods:

Shipping of specimens shall be done by a TDG certified individual in accordance with TDG regulations. For additional information regarding classification of specimens for the purposes of shipping, consult either Part 2 Appendix 3 of the TDG Regulations or section 3.6.2 of the IATA Dangerous Goods Regulations as applicable.

Patient Criteria:

Suspected Powassan infection. Submitted samples will first be analysed by the Viral Zoonosis Diagnostic Laboratory by Powassan HAI to determine if the patient has developed anti-flavivirus antibodies. Samples that are reactive can be further analysed for the presence of neutralizing antibodies. Samples that are HAI non reactive (negative) will not be tested by PRNT. This is not a routine test. Please contact the Viral Zoonosis Diagnostic Laboratory before sending specimens.

Accompanying Documentation:

Completed Viral Zoonoses requisition including sender laboratory name, address and telephone number. Patient name and / or identifier (specimen reference number), date of birth, test(s) requested, collection date of specimen, date of on-set of symptoms, and clinical and travel history of patient.

Comments:

This is not a routine test. Please contact the Viral Zoonoses Diagnostic Laboratory before sending specimens.

Methods and Interpretation of Results:

Antibodies directed towards members of the JE serocomplex viruses (Dengue, Saint Louis Encephalitis, POW, etc.) can cross react significantly in some serological assays. The PRNT is a more specific assay and can be used to document the presence of serum antibodies specific for a particular flavivirus. Serum samples are incubated with virus and if viral neutralizing antibodies are present, they will bind to the Powassan virus and prevent viral infection of cultural cells, and hence a reduction in the number of plaques detected. The neutralizing titre of a sample is expressed as the reciprocal of the serum dilution at which there is a 90% reduction in the number of plaques detected. If the patient has experienced more than one flavivirus infection, cross reactive results may yield uninterpretable results with this assay despite increased specificity.

Due to the cross-reactive nature of flavivirus antibody, the detection of flavivirus IgG (Eg. JE, dengue, etc.) in a single sera is indicative of past or present exposure to this agent, or a related agent from the same virus genus. The presence of POW specific IgM in a single serum sample is consistent with an acute infection to this agent (or a related flavivirus, note that flavivirus IgM serological procedures are more specific than IgG serology for this genera of arboviruses) and meets the criteria for a "probable case". However, a 4 fold rise or greater in neutralizing (PRNT) or total antibody (HI) titre is required to document a "confirmed case" of infection with associated illness.
There is increasing evidence for IgM persistence in blood/serum for up to a year or more after arbovirus (Eg. members of the Flavivirus, alphavirus, and bunyavirus arthropod borne virus groups) exposure. Thus, detection of IgM by itself may not always be a confirmation of acute infection.  
Isolation of an arbovirus, or detection of arboviral antigen or nucleic acid in a clinical specimen would constitute firm evidence of viral association with illness and provide "confirmed case" status.
Turnaround Time:

14 Calendar days after the completion of HAI testing.

Contact:
Phone #: (204) 789-6071
Fax: (204) 789-2082
Email: NML.Viral.Zoonoses@phac-aspc.gc.ca
References:
  1. WHO. 2007. Guidelines for plaque reduction neutralization testing of human antibodies to dengue viruses.
Fact Sheets:

Powassan encephalitis virus - Material Safety Data Sheets (MSDS)

Guidelines:
Related Information: