A risky experiment

According to an excellent news report by Helen Branswell, CDC is about to embark on a risky, but probably necessary, experiment. With the potential for a catastrophic pandemic with influenza A(H5N1) ("bird flu"), certain basic questions need to be answered, chief among them, how easily can the avian virus exchange genes with influenza strains already circulating in human populations. In a recent post we worried about the danger of this happening in the thousands of workers engaged in culling infected birds across southeast and east asia as a result of co-infection with both viruses. In the CDC experiment, a 2004 influenza A(H5N1) strain will be intentionally mixed with currently circulating human influenza A strains, H3N2 and H1N1. The work is designed to test the ease with which reassortment can happen and also test various constructed gene combinations from both viruses to see if they can produce the feared human-adapted virus that retains high pathogenicity.

If this sounds risky, it is. The work will be done in an "enhanced BSL3" laboratory--not the highest security but close to it. Viral particles will be tested in animals for disease causing potential and transmissibility. While stringent laboratory procedures will be specified, it is not clear exactly what precautions will be taken with laboratory workers potentially exposed to the virus, e.g., will they be kept under observation and allowed only limited contact with the public during and for a short time after their work with live virus?

The objective is to obtain some quantitative information on risk. According to WHO's Klaus Stohr, "It will give us an opportunity to predict the probability because we will have an understanding on the number of reassortment viruses which are viable, the percentage of those that are viable which are then transmissible - and also on the percentage of those which are viable, transmissible and pathogenic. And how pathogenic they are."

Branswell's news article also contained the somewhat disquieting information that CDC has already done some work on H5N1 hybrids:

CDC researchers have already made hybrid viruses with H5N1, using versions of the virus isolated after it first caused human infections in 1997 in Hong Kong.

"Some gene combinations could be produced and others were not," is all [CDC scientist Nancy Cox] will reveal of that as-yet unpublished work.

It seems to this observer that reliable scientific information on this topic is of such urgency it should be released on a continuing basis, not wait for the usual peer-review process to unfold. The scientific community can do its own peer-review if sufficient technical details of the experiment are released at the same time. We urge CDC to provide all information on these experiments on an expedited basis.