November 10, 2014 – PCR and Ebola

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Anchor lead: Why can’t a standard laboratory test be used to screen people for Ebola virus infection? Elizabeth Tracey reports

Why can’t a standard laboratory test known as ‘PCR’ determine whether someone is infected with Ebola virus rather than quarantining people for three weeks and watching for symptoms?  Stephen Desiderio, director of  the institute of basic biomedical sciences at Johns Hopkins, says there are a couple of issues.

Desiderio: They want a test that you can read almost immediately. Like a stick test.  If you’re using real time PCR and fluorescent probes it might take on the order of an hour or two to do the test and they want something that’s quicker.  :12

It’s also necessary for the infection to have progressed far enough that a quantity of virus can be found in the blood.

Desiderio: A thousand viral particles per ml of blood would give you sufficient virus to do it. That would be about the limit of detection would be about that level.  :09

Desiderio says other issues such as handling of specimens and copying the virus efficiently are also problematic, so for now, symptoms must first develop before screening is likely to be useful.  At Johns Hopkins, I’m Elizabeth Tracey.