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In vitro infectivity of WNV ID NAT reactive plasmas that are positive for antibodies. Maria Rios, Ph.D. CBER/FDA Blood Product Advisory Committee July 22, 2005. Background. All reported cases of WNV transmission by blood transfusion have occurred during the acute, viremic phase

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In vitro infectivity of WNV ID NAT reactive plasmas that are positive for antibodies

Maria Rios, Ph.D.

CBER/FDA

Blood Product Advisory Committee

July 22, 2005


Background
Background

  • All reported cases of WNV transmission by blood transfusion have occurred during the acute, viremic phase

  • WNV NAT is the most appropriate strategy to interdict infectious donations

  • WNV MP NAT has been implemented; MP NAT rate-triggered ID NAT identifies additional, low viremic units that are often antibody positive

  • Low titer viremia can persist up to months after IgM and/or IgG seroconversion

  • We lack of data on WNV transmission by late acute phase donations currently identified as MP NAT (-), ID NAT (+), IgM and/or IgG (+)


Wnv infectivity questions and options
WNV infectivity - Questions and Options

  • Questions

    • What is the minimum infectious dose for WNV?

    • Are antibody (+), MP NAT (-), ID NAT(+) units ever infectious?

  • Options for studies

    • Recipient lookback is costly and complex

    • Animal models

      • Small animal models for WNV infectivity (mice and hamsters) don’t take volume of plasma that could simulate transfusion practice

      • Non-human primates – Baboon, Rhesus Macaque, Chimpanzee are more suitable

    • In vitro studies were performed to address protective function of antibodies to WNV infection

      • Vero cells

      • Human primary monocytes/macrophages


In vitro infectivity of WNV NAT and IgM and/or IgG Positive Plasmas

Single donor monocyte

Vero cells cultivated to 80% confluence

Cells cultivated in

DMEM + 10% FBS + M-CSF (1,000U/mL) + Gentamicin (10µg/mL)

Culture for 10 to14 days

Infection: medium removed, 0.5 mL of WNV +ve plasma + 4.5 mL of fresh medium added and incubated for 2 hr under gentle rocking

Culture medium containing 10 mL of fresh medium added and incubated at 37oC and 5% CO2

Culture observed daily for CPE

and/or TaqManin culture supernatants



Conclusion
Conclusion without antibodies

  • Several WNV positive plasmas containing IgG and/or IgM were infectious for Vero cells and/or human MDM in vitro.

  • Although, in vitro infectivity does not imply infectivity in vivo, it demonstrates the presence of live virus and therefore raises concern about a potential risk for transfusion transmission.

  • The potential transfusion risk from low titer/antibody positive donations needs further study either through recipient lookback or an inoculation study in non-human primates.


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