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Detection of Antibodies Directed Towards Powassan Virus by PRNT

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Requisition Forms

Reference Details


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

Test Category:
Powassan virus
Illnesses and Diseases:
  • Powassan encephalitis

Serum. Minimum volume of 250 µl required.

Collection Method:

2 mL screw cap 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.

For additional guidance on the transport of infectious substances in other languages, please click on the link below.


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.


This is not a routine test.  Please contact the Viral Zoonoses Diagnostic Laboratory before sending specimens.  Specimens positive by Powassan HI will be forwarded for Dengue and Powassan PRNT confirmation to determine potential flavivirus cross reactivity.

Methods and Interpretation of Results:

Antibodies directed towards members of the tick-borne encephalitis serogroup of viruses 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 anti-flavivirus antibody, the detection of anti-POW virus antibodies by HI is considered a “probable case”. However, a 4-fold rise or greater in neutralizing (PRNT) titres in comparison to Dengue is required to document a “confirmed case” of infection with the associated illness.

Isolation of an arbovirus, detection of specific antibody by plaque reduction neutralization assay or detection of nucleic acid by Real Time RT-PCR 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.

Phone #: (204) 789-6097 or (204) 789-2106
Fax: (204) 789-2082
  1. WHO. 2007. Guidelines for plaque reduction neutralization testing of human antibodies to dengue viruses.
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