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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

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 id nat reactive plasmas that are positive for antibodies

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.