Re: UK poultry worker 'has bird flu' (H7)
Flu virus missing?
- 13 May 2006
- From New Scientist Print Edition.
- Ian Brown Weybridge, Surrey, UK
In response to the article claiming the UK's bird tests may be missing the avian flu virus, I would like to say that the British testing programme is intended to detect the incursion of H5N1 into the UK via wild bird populations (15 April, p 12). This is based upon the detection of viral nucleic acid using the polymerase chain reaction (PCR). Björn Olsen refers to surveillance for the "virus" itself in his programme surveying healthy wild birds. The survival of infectious virus may well be enhanced in aqueous solution but our laboratory testing is based upon the detection of viral RNA that is present even when infectious virus does not survive.
Studies are in progress to produce validated data on virus survival in different media, but unpublished data from experimental studies here at the Veterinary Laboratories Agency indicate good viability of viral RNA on dried swabs stored at 4 °C. Placing faecal material into aqueous solution may be detrimental to the stability of the RNA if the pH is not buffered to neutral values. The procedures used conform to international protocols endorsed by the European Union's wild bird surveillance programme.
We have not seen the validation data relating to the method used by Olsen but direct comparisons between "dried swabs" and the use of transport medium will be important. The survival properties of viruses in different environments and media are currently being studied at the VLA, and part of this will be stability of virus from faeces.
From Graeme Laver
The survey you reported seems to have isolated fewer than expected avian influenza viruses from wild birds in the UK, and the way the samples were collected and stored could be to blame. On one of our trips to the Great Barrier Reef in the 1970s we collected 642 cloacal swabs from healthy shearwaters and terns, from which we isolated nine low-pathogenicity influenza viruses. Other surveys seem to have had a similar isolation rate.
We used dry swabs to collect the samples from the birds' cloacas. These were immediately put into tubes containing 2 millilitres of tissue culture growth medium and then snap frozen in liquid nitrogen. The samples were never allowed to dry out or stored at the temperature of a domestic freezer, which would have destroyed the virus, for sure.
Nowadays, cloacal samples are tested for virus using PCR to amplify RNA, so virus in the samples does not have to be kept "alive" unless viable virus is required for further experiments. If liquid nitrogen is not easily available, cloacal swabs for PCR can be put straight into ethanol, which destroys the virus but preserves the RNA.
I don't know if the refrigerated swabs that had dried out (as reported in your article) were still suitable for PCR analysis, but I suspect from the results that they were not. But why on earth do this? Putting the samples into ethanol is no big deal.
Murrumbateman, New South Wales, Australia
Debora MacKenzie writes:
<SYMBOL SRC="/data/images/archive/maths/bull.gif"></SYMBOL>We asked the UK's Department for Environment, Food and Rural Affairs, which runs the VLA, whether it would evaluate different methods for preserving bird flu virus in field samples. DEFRA said it is "looking into the possibility of conducting a trial in this area".
From issue 2551 of New Scientist magazine, 13 May 2006, page 22
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Printed on Mon Feb 05 14:15:22 GMT 2007
http://www.newscientist.com/article.ns?id=mg19025510.100&print=true
