A steady-handed technician in a long white labcoat injects a serum into two tiny holes in a live egg, the first step in a process to identify the deadly avian influenza virus. Because it is only a mock test, several observers calmly gather behind her. If the sample were live and potentially contagious, the scene would not be as tranquil.
When handling live samples, the Veterinary Laboratory Agency (VLA) in Weybridge, south-west of London, transforms into a high-security "Category 3" laboratory.
The lab building is negatively pressurised, so that no microbes can escape. Scientists and technicians must strip fully and don clean lab clothing upon entry, and undergo a sterilising shower when leaving.
To avoid exposure, scientists work in a sealed cabinet through glove portals, carrying out their work behind a glass pane.
The precautions are necessary at the busy laboratory because it handles all suspicious bird samples from the 25-nation European Union as the Community Reference Laboratory, or the foremost authority, on avian influenza.
VLA scientists work with veterinarians from around the world to test and identify bird viruses and monitor Britain for signs of an outbreak. If the worst does occur, the agency must be ready and flexible with an emergency response.
Already this year, the Weybridge laboratory has discovered the H5N1 bird flu strain in a parrot quarantined in Essex, in the east of England, and in birds found dead in Croatia, Romania and Turkey, prompting import bans from the affected areas.
"We're very much an international laboratory," said Steven Edwards, chief executive of the VLA.
He said the VLA's Community Reference Laboratory status "gives us a co-ordinating role, not just in the UK but with other national reference laboratories in other member states".
The VLA, which is made up of the central laboratory at Weybridge and 16 other British laboratories, works with animals of all types, conducting millions of tests every year to diagnose infected species or conduct directed government research.
Though the exact number of bird flu samples tested in the most recent wave is not available, the VLA tested 426 virus samples in 2004, of which 181 were identified as influenza viruses.
The H5N1 influenza strain has killed scores of people and devastated poultry stocks in Southeast Asia.
About 15 scientists are normally working on avian influenza research at the lab, though 25 or more may be dealing with it during periods of heightened urgency and even more could be diverted in an emergency.
Testing a sample for the influenza virus can take anywhere from two to six days. Scientists import samples, which can be fecal swabs, lumps of tissue, or viruses isolated by other laboratories, and use them to innoculate live eggs, allowing the virus to grow in the embryos.
After two days, amniotic fluid is drawn from the embryos and combined with red blood cells to see if the virus sticks the cells together into a matrix, a process called hemagglutination. The influenza virus will cause the blood cells to stick together, while most other viruses will not.
Scientists use various antibodies to determine the specific type of virus; H5 and H7 are avian strains dangerous to humans. Up to 154 different types of influenza are possible, including the normal human varieties.
The test may give an initial positive for influenza, but if preliminary results are negative, the scientists will wait up to six days to allow the virus to grow before confirming the sample is not infected with influenza.
Once scientists have confirmed the strain of the virus, it is analysed for its molecular and genetic composition, which allows researchers to compare it to previously identified strains of the virus.
The genetic information is extracted from the virus, then dyed so that each type of protein in the DNA sequence is a different color. A machine called a Genetic Analyser uses a laser to map the gene sequence.
Scientists also can test how pathogenic the virus is by injecting it into live birds, and judging its power by how the birds are affected.
Ian Brown, head of avian virology at the lab, reports to Britain's Department for Environment, Food and Rural Affairs and the World Organisation for Animal Health if a sample is found to test positive for bird flu.
No birds have been found positive for bird flu in Britain since the parrot, imported from Surinam, died in quarantine in Essex alongside birds which had been brought in from Taiwan.
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