17:06 18 March 03
NewScientist.com news service
A new gene-based technology may soon allow exposure to mystery biological weapons to be identified in a few hours.
Experts say that if this early detection means treatment is highly effective, then the harm that can be caused by biological weapons would be substantially lessened, reducing their attractiveness to attackers.
A person's cells react almost immediately after exposure, according to US army scientists, and the combination of genes expressed is unique for each biological agent. So by examining gene expression, it is possible to rapidly identify the agent, as well as the level of exposure, and tailor treatment accordingly.
Marti Jett, at the Walter Reed Army Institute of Research in Silver Spring, Maryland, and colleagues identified unique patterns of gene expression in primates and pigs following exposure to a range of bioterror agents. They believe a handheld test for humans could be developed within a year or two.
Jett told New Scientist that if victims of an anthrax attack, for example, were identified within 36 hours of low dose exposure they have a 100 per cent chance of survival, compared with only 50 per cent if diagnosis takes place after three days.
"It sounds rather wonderful," says John Oxford, a virologist at Queen Mary, University of London. If such a method of early detection was widely available, "it would knock the bottom out of bioterrorism - they would have to go back to the old Semtex", he says.
Plague and cholera
Jett's team exposed non-human primates to low doses of eight potential bioweapons: anthrax, plague, brucellosis, Venezuelan equine encephalitis, dengue fever, Staphylococcal enterotoxin B (SEB), cholera and botulinum toxin.
At the doses given, symptoms appeared only after three days. Without treatment, the primates would be dead by seven or eight days. But the team saw characteristic changes in gene pattern, detected by the analysis of messenger RNA in blood samples, as early as 24 hours.
And Jett thinks it will be possible to cut this time to just six hours. Such tests could be vital in situations where people were in the vicinity of a biological attack but unsure if they were exposed.
Experiments giving different doses of SEB to pigs showed that gene expression not only indicated the agent but also the level of exposure, successfully distinguishing lethal and non-lethal levels.
Handheld device
Many of the activated genes are in the white blood cells, the first line of the body's immune defence. The most useful are genes that are not usually expressed in healthy individuals.
As few as 50 genes are indicative of each pathogen, says Jett, but for reliable identification a few thousand should be tested. The team used laboratory equipment that could analyse about 40,000 genes per sample. A commercial handheld device analysing 400 genes will be on the market within a year, Jett says, and companies are developing portable devices that can analyse far more.
The team is now testing the gene expression resulting from normal diseases, to ensure that these will not be confused with bioweapon exposure. For example, the initial symptoms of anthrax and influenza are similar.
"If this technology can be applied to the huge natural killers of mankind like influenza, then it would be a really significant discovery," Oxford adds. "They're on to a winner in every sense."
Jett's team's findings were presented at the recent American Society for Microbiology's biodefense research meeting in Baltimore, Maryland.
Shaoni Bhattacharya