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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 • 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 • 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
In vitro infectivity of WNV positive plasmas with and without antibodies
Conclusion • 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.