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NS 27 oct 2001

Out of the blue
Another attack could come at any time, anywhere. Is there a way to protect ourselves? NS 27 oct 2001

THE line has been crossed. Even if those responsible for the recent anthrax mailings are caught, another attack could come without warning. So what should we do?

The US Postal Service is looking at technologies that could sterilise mail, such as ultraviolet light. But terrorists could easily find another means of delivery. Vaccinating millions of people against an attack that may never happen isn't practical. All vaccines can cause side effects, and the anthrax one doesn't give full protection against all strains.

Researchers are working on better treatments (see opposite), but at the moment antibiotics only work if given early enough. That means the key to saving lives is to detect an attack as soon as possible. But identifying anthrax isn't easy. There are some "quick and dirty" field tests. An antibody test can give results within 15 minutes. But Bacillus anthracis is incredibly similar to its harmless and more common bacterial cousins, and it's not clear how specific the test antibodies are. That means the tests can give false positives.

'THESE TECHNOLOGIES WON'T BE READY FOR SOME TIME. AND EVEN YMEN DETECTORS ARE AVAILABLE, THEY ARE NOT GOING M COME CHEAP'

It's also why the next step is usually PCR, a technique that amplifies tiny amounts of DNA. A specialised machine the size of a bread box made by Cepheid of California can now detect anthrax DNA within 30 minutes. A positive PCR result is very reliable, says Calvin Chue of the Center for Civilian Biodefense Studies at Johns Hopkins University in Baltimore. The problem for health officials is that negative results don't prove spores were absent. Both DNA and antibody tests rely on cracking open the tough spores. But the solutions used to do this can inhibit the PCR reaction. That's why the gold standard for anthrax testing still consists of growing the bacteria in different environments. This can take days. And the main problem with all these tests is that they are only done if an attack is suspected. What if someone manages to disperse spores over a crowd without anyone noticing? What officials would really like is a quick and easy way to test the air from a distance. Several groups are already working on "smoke detectors" for bioweapons, and remote detection from several kilometres away might be possible, too. At the Lawrence Livermore National Laboratory in California, Page Stoutland and his team have built an antibody-based machine the size of a mailbox that sucks in air, checks for anthrax or other bacteria, and radios an alarm station if it finds anything. "The goal is to have something that sits there 24/7, detecting agents," says Stoutland. But if there is a chance of false alarms as with other antibody tests, organisations may be reluctant to use such machines. At Johns Hopkins University, however, Wayne Bryden's team is developing a mass spectrometer built into a detector the size of a large suitcase, which he says can distinguish between anthrax and its harmless relatives. He hopes to have a prototype ready soon.

For detecting bioweapons remotely, one technology that has already had some success is LIDAR, the laser analogue of radar. A helicopter-mounted system developed at Los Alamos National Laboratory fires powerful laser pulses at a suspect cloud. The reflected light reveals the size and density of the particles. If all are the same size, the cloud is likely to be artificial. But LIDAR doesn't reveal the type of bacteria. So researchers shifted to ultraviolet wavelengths, which can yield signals unique to different pathogens up to 12 kilometres away. Still, the system cannot distinguish between anthrax and very similar bacteria. One solution may be to use super-strong laser pulses to burst the spores, releasing compounds that a detector can spot. But these technologies won't be ready for some time. And even when detectors are available, they are not going to come cheap. Bryden's machine could cost hundreds of thousands of dollars. While key government sites and public places might install such devices, elsewhere vigilance and old-fashioned culture tests look likely to remain our main defence against anthrax. Sylvia Pagbn Westphat and Catherine Zandonetia

Critical Moments
An antidote to anthrax's killer toxin could buy time and save lives

IF AN anthrax attack isn't detected quickly, it may be too late to help the victims. But ways of blocking the bacterium's deadly toxin could one day buy precious time for antibiotics to take effect.

Anthrax toxin is made up of three components called protective antigen (PA), lethal factor and oedema factor. Individually they are harmless. But after protective antigen has bound to a receptor on the surface of cells, it combines with lethal factor and oedema factor. The complete toxin can enter cells, and when it gets inside immune cells called macrophages, it chews up key enzymes and kills the cells.

Exactly how this kills people is unclear. Death is preceded by massive internal bleeding and shock, so one possibility is that the emergency chemical signals, or cytokines, released by the dying macrophages wreak havoc on the body's blood-clotting systems. Antibiotics are usually useless once symptoms appear, as enough toxin has already been produced to kill, even if the antibiotics destroy all the anthrax bacteria.

'There are a number of clever ways being developed to block the toxin,' says John Young of the University of WisconsinMadison. He and his colleagues have found the receptor for the toxin. When they synthesised the fragment of this receptor that sticks to PA, they found that it works as a decoy, mopping up the antigen before it attaches to cells. The fragment could be used to develop drugs that do the same job, Young says.

Jennifer Maynard at the University of Texas at Austin and her team have taken a similar approach, developing super-sticky antibodies that stop PA from attaching to the receptor. She has 'bred" existing mouse antibodies in the lab so that they stick to PA 50 times as strongly as before, blocking its ability to dock with cells, she told an anthrax conference in June. 'For postexposure treatment, antibodies are promising, " she says. The antibodies could also be developed for use as a highly sensitive, rapid diagnostic test. Maynard is waiting to publish her findings before going public, but says that tests on rats are "encouraging'.

Other researchers are targeting different aspects of toxin function. John Collier and his team at Harvard Medical School have developed molecules that stop the toxin ftom assembling, while Robert Liddington's grbup at the Burnham Institute in Calffornia has discovered the structure of lethal factor, the part of the toxin that destroys cell enzymes. The work could pave the way for rapid drug development.

Blocking the toxin alone is unlikely to be a miracle cure, according to Harry Smith of Birmingham University, who discovered the toxin in the 1950s. 'It would have to be pretty good to have an effect,' he says.

But extending that crucial time window during which antibiotics can be used is vital. 'To have something, even if it's not a miracle bullet, should help quite a bit,'

says Maynard. Claire Ainsworth More at: Nature Biotechnology (vol 19, p 958)

Red hot legacy

Leaks from a Soviet plutonium factory may still be causing cancer

THE Soviet Union covered up two nuclear accidents that happened decades ago at an atomic bomb factory in Siberia, say Russian scientists who've dated stray radioactive particles from a local river. By keeping the accidents secret the Soviets placed thousands of residents living downstream of the plant at risk from cancer. The radioactive contamination could still be a threat today. Krasnoyarsk-26 was one of the Soviet Union's three big secret atomic bomb complexes. Built inside a hill 50 kilometres north of Krasnoyarsk in the 1950s, the complex housed three reactors making plutonium.

Two reactors, closed down in 1992 and 1993, discharged their primary cooling water directly into the Yenisei river, which flows over 3000 kilometres north into the Kara Sea, then on into the Arctic Ocean.

Alexander Bolsunovsky from the Russian government's Institute of Biophysics in Krasnoyarsk uncovered 11 of 12 "hot particles" that turned up along the banks of the Yenisei between 1994 and 1999. These highly radioactive fragments of reactor fuel, containing isotopes of caesium, plutonium and strontium, were up to 330 kilometres away from the nuclear plant.

With the help of the Vernadsky Institute of Geochemistry and Analytical Chemistry in Moscow, Bolsunovsky has now estimated the age of the particles by analysing the ratio of two isotopes, caesium-137 and caesium-134, which decay at different set rates. He concludes that eight were formed around 30 years ago, and four around 20 years ago, suggesting they came from two separate leaks from the Krasnoyarsk reactors.

Levels of contamination in the past 30 years could have been high enough to cause the excess of cancers local doctors have picked up in riverside communities, Bolsunovsky told New Scientist. 'The residents of the nearby villages had no idea of the hazard and could have received enormous doses.' The Soviet authorities kept the accidents a secret, he says.

Villagers still face a risk today. Spending a few hours within a metre of a particle could mean radiation doses in excess of the annual Russian safety limit of one millisievert.

The Russian Ministry of Atomic Energy has always denied that there have been any accidents at Krasnoyarsk-26, now known as Zheleznogorsk. But Murdoch Baxter, who used to head the International Atomic Energy Agency's marine laboratory in Monaco, says Bolsunovsky's evidence is convincing. "In the past the Ministry has cast doubts on the quality and completeness of the early reported data on such particles. This paper is likely to dispel such doubts.' Rob Edwards More at: Journal of Environmental Radioactivity ivol 57, p 167)

Other Earths
OUR galaxy may contain hundreds of thousands of life-bearing planets, according to a new estimate. This could make the nearest inhabited twin of planet Earth as close as a few hundred light years away.

In 1961, the American scientist Frank Drake suggested a simple formula for calculating the number of technologically advanced civilisations in the Galaxy. But the Drake equation contains a number of parameters that are very difficult to estimate, such as the number of Earth-like planets around other stars and the percentage of these planets that are likely to evolve life.

Now Siegfried Franck and a team of German climate researchers from the Potsdam Institute for Climate Impact Research near Berlin have set new limits on these parametvrs. Franck's team first calculated how many planets lie in a star's habitable zone the region where the temperature allows photosynthesis. They arrived at a figure of half a million "Galas", as they call extrasolar terrestrial planets with a globally acting biosphere. 'Because we also allowed for the fact that the habitable zone of any star will migrate and shrink as the star evolves, our number is much lower than earlier estimates," says Franck.

Their estimate is also conservative in other respects. Based on theoretical arguments, the team assumed that only one per cent of all stars in the Milky Way is accompanied by Earth-like planets. They also assumed that life will form and evolve on only one per cent of all habitable planets. "Some people believe this factor to be 100 per cent," says Franck.

Although many variables remain utterly uncertain, Franck's work is useful in setting an upper bound on the number of Gaias, says Alan Boss of the Carnegie Institution of Washington, DC. "If Earths turn out to be commonplace, then they will not have overestimated the number of life-bearing planets greatly, but if Earths turn out to be rarer, then their estimate may be too high by several powers of lo." But other researchers are sceptical. "It is a very good paper," says Donald Brownlee, an astronomer at the University of Washington in Seattle, "but we have no way to know if the estimate is good or not. We have no data." Other astronomers think the conclusions of Franck's team are premature. "We don't know enough to predict habitability," says planet hunter Geoffrey Marcy of the University of California in Berkeley. And there are other unknowns Franck has not taken into account. For instance, as Brownlee and others have suggested, a star's position in the Milky Way may play an important role in the development and sustenance of Earth-like planets and life. The only way to find out is to observe extrasolar Earth-like planets for real. "That may actually happen within the next several years if NASA decide to fly the Kepler mission," says William Cochran of the University of Texas in Austin. Kepler should reveal how common terrestrial planets are, and produce statistical data on their orbits and sizes. Govert Schilling More at: Naturwissenschaften, vot 88, p4l6

Head in the Clouds
COSTA Rica's aggressive conservation policy may not be enough to protect its rare and celebrated cloud forests. The mountain rainforests are ring-fenced in protected parks. But a new study reveals that they are being damaged by lowland deforestation further down the hill. Cloud forests such as those at Monteverde contain some of the richest assortments of tropical plants and animals in the world. The clouds form when warm lowland winds blow up against steep mountains, causing the air to rise and shed moisture as clouds.

In 1999, scientists noticed that Monteverde's cloud bank was gaining altitude and failing to blanket the mountain in mist, possibly triggering the demise of several species of frogs. Scientists linked the lifting clouds to rising Caribbean Sea temperatures due to global warming (New Scientist, 8 May 1999, p 32). But Robert Lawton of the University of Alabama in Huntsville has discovered that lack of lowland forest may be the decisive factor. 'We didn't realise the deforestation of the lowlands was destroying the cloud forests," he says. Despite the complex of public and private reserves littering Costa Rica, the lowlands have received little protection-only 18 per cent of the original vegetation from the beginning of the last century is still there. Lawton's team studied daily satellite photos and found far fewer clouds over the deforested lowlands that lie directly east of Monteverde compared with forests in neighbouring Nicaragua, where considerably less lowland trees have been destroyed. The clouds in Costa Rica were also higher, as estimated from the clouds' shadows, the land elevation, and the known position of the Sun. The researchers fed their information into a computer model of the local climate and found that the clouds hung at 1100 metres over lowlands covered with pasture, but at 650 metres over forested lowlands. The model suggests the air over pastureland is warmer and drier, forcing it to travel higher into the sky before it forms clouds. Stephen Schneider, a Stanford University biologist who found the link to global warming, says both deforestation and global climate change could be having an impact. He says cloud forests could act like "coalminers' canaries", giving an early warning of the damage that local and global changes can have on an eco-system. Catherine Zandonelia More at: Science (vot 294, p 5841

Reclaiming the Desert
With only a few sheep and a shovelful of dung, [ocal farmers are reclaiming their land from the Sahara. Fred Pearce reports

IT MUST be true. We've been told it so many times. The over-farmed and overgrazed soils of Africa, especially on the fringes of the Sahara, are losing their fertility and eroding away. As the population grows, poor farmers are mining the last goodness from their soils. Their animals graze the grasslands away to nothing and the desert sands move in. Environmentalists say it; development economists say it; politicians say it; soil scientists say it. "An area the size of Somalia has become desert over the past 50 years. The same fate now threatens more than one-third of the African continent," says the UN Food and Agriculture Organization, adding that "the main cause is mismanagement of the land." Its sister body the UN Environment Programme claims that 900 million Africans face starvation as their soils crumble away. UNEP masterminded a UN Desertification Convention in 1996 in an effort to reverse the trend. But out in the shimmering heat of and Africa, where tens of millions of farmers scratch a living from the soil, new research suggests that this apocalyptic vision is little more than a mirage. Farmers are finding ways to intensify their farming methods without destroying their soils. Farm yields are often up, not down. Soils are often getting better, not worse. Fast-growing populations continue to be fed. In places the desert sands are even retreating. Indeed, for most places at most times, the whole notion of desertification increasingly looks like a myth.

Consider the dusty desert margins of northern Nigeria around the ancient caravan city of Kano, for example. Here, population density has soared to levels similar to Belgium, and some 85 per cent of the land is now cultivated. Rainfall is declining, the availability of chemical fertiliser has fallen by 80 per cent, and only the richest farmers can afford high-yielding grain varieties or irrigation. The poor make do with small scraps of sandy soils. Surely these fields should be turning to desert dust as yields plummet, hunger spreads and refugees head for the cities?

But that's not what I saw when agricultural scientist BB Singh, who heads the Kano office of the International Institute of Tropical Agriculture, drove me through the area this summer. The dusty roadsides between the closely spaced villages were busy with fruit and vegetable stalls and behind them the fields were already green with bushes laden with the first cowpeas. Under the burning sun, we visited Ado, a farmer who tends a 2-hectare plot on the outskirts of Badume village, 50 kilometres northwest of K-ano. Ado was exultant. The previous year, he had harvested just two bags of cowpeas from his plot. This year, he got seven bags for the same effort. He took me behind the high mud walls of his compound to an inner sanctum where the reasons for his success were bleating. He used to let his sheep roam free. Now he had half a dozen of the animals tethered in his backyard, munching away at straw left over from his fields and creating a large pile of manure for fertiliser. The last mound of muck had been shifted just a few days before to fertilise the next cowpea crop.

'THOUGH THE POPULATION HAS RISEN FIVEFOLD, THESE HILLS ARE GREENER, LESS ERODED AND FAR MORE PRODUCTIVE THAN BEFORE'

Sheep manure is transforming Ado's life. "Now I can send my three children to school," he said. "The boys will become farmers, but I want my daughter to become a doctor. " His neighbour Galadima was doing the same thing on his six hectares. 'Crops grow much better with manure,' he told me. 'i don't use chemical fertiliser at all now that I have manure.' His two wives and 18 children came running out of the house and lined up for a family photo. They all looked well fed.

Singh's researchers are monitoring the effects of sheep manure in Badume, and he confirms Ado's interpretation of his success. But there's another reason for Ado's progress, Singh adds-planting leguminous crops such as cowpeas, which fix nitrogen from the air and deposit it in the soil. Frances Hams, a soil scientist at Kingston University in Surrey, agrees that these two strategies work. "The zone has supported intensive cultivation for many years without suffering from land degradation," she says. "The key is the integration of crops and livestock, because it enhances nutrient cycling." Legumes and manure put back what the grain crops take out.

As a result, the Kano region is the most agriculturally productive part of the country and farm yields of sorghum, millet, cowpeas and groundnuts are growing rather than dwindling. All this in a region where many experts believe only irrigation can produce worthwhile crop yields. Back in his small office in a back street of Kano, Singh is adamantly optimistic. 'Even less than 300 millimetres of rain is enough for good crops. We can double yields here easily and improve the environment at the same time. And this is nothing unusual. We can do it all over Africa."

Harris makes another point-far from being a liability, the high local population densities are actually essential to this form of intensified farming. In a land where tractors are rare, people provide the labour to tend fields, feed animals and spread manure. The old environmental shibboleth that rising populations trigger soil abuse and desertification is being tumed on its head here. As is the idea that livestock are an environmental curse. Far from it, livestock can be an ally of better farming. All this would be a mere curiosity if the Kano story was a one-off. But similar stories are emerging ftom all along the Sahara's edge, from Niger and Senegal, Burkina Faso and Kenya. David Niemeiier, an environmental geographer from Wageningen University in the Netherlands, has spent the past seven years studying the soils of eastern Burkina Paso. "I went there expecting to find widespread land degradation, especially in the most densely populated areas," he says. After all, the area had seen a decline in rainfall and a tripling of population over 40 years. 'But there was no evidence of land degradation connected to human activities. Nor was there any decline in farm productivity. In fact yields of many crops had risen sharply." Rice and maize yields per hectare have tripled and sorghum, millet and groundnuts doubled, says Niemeijer. And when he compared soil fertility today with data collected during a French survey in the late 1960s, he found no evidence of declining nutrients. He looked at changes in four different nutrientsnitrogen, carbon, phosphorus and potassium@n five different soil types. In 14 of the 20 wmparisons, there was no significant change from the 1960s data. Of the remaining six, four showed an improvement and two a marginal decline in nitrogen. Phosphorus levels were actually higher in cultivated soils than in fallow land. The results were the same for areas with high and low population densities. Almost all the variation in farm yields, it turned out, was down to rainfall.

So, what are farmers doing right? This is no high-tech breakthrough, nor a result of Western aid programmes. Farming methods remain mostly traditional, with few chemical inputs. Niemeiier's colleague, social scientist Valentina Mazuccato, asked the farmers their secret. 'They do not need to invent new management systems as land becomes more limited. All they do is apply some of these,soil and water conservation practices more intensively," says Mazuccato. They erect low walls of stone and earth to keep soil from washing off sloping land in the occasional heavy downpours. They spend more time weeding and thinning crops to improve yields without depleting soils. But above all, they intensify their systems of cooperation, forming gangs to tend each others' field during busy times, and lending and borrowing land, livestock and farm equipment. They swap seed varieties assiduously. Whatever they are doing, it's working. Burkina Faso produced 36 per cent more food in 1998 than it did just eight years earlier, and per capita food production is 20 per cent higher than in 1970. 'I am optimistic," says Niemeijer. "Of course life remains hard. These farmers are still never sure if they can feed their family, and they are not always in control of their destinies. But things are not going down the drain." If farmers can maintain soils as they intensify production, can they also use such techniques to rescue their land once it has begun a slide into desertification? The evidence is that they can. Boubacar Yamba of the University of Abdou Moumouni in Niamey, Niger, says that 20 years ago the Maradi district in southern Niger was facing environmental crisis after repeated droughts. Average rainfall was down 30 per cent, the population had doubled in 25 years, soils were crumbling and the last forests were being cut down. Yet, though the rains have never returned to former levels, the millet farmers have fought back, diversifying into growing vegetables, trees and nuts and tending livestock. Desertification has gone into reverse.

But perhaps the best researched example comes ftom Kenya. Sixty years ago, British colonial scientists wrote off the eroding, treeless hillsides of the drought-prone Machakos district of Kenya, east of Nairobi. Soil inspector Colin Mather called those bare hills 'an appalling example" of environmental degradation. The local Akamba people, he said, 'are rapidly drifting to a state of hopeless and miserable poverty and their land to a parched desert of rocks, stones and sand'. Similar reports came in the 1950s and again in the 1970s.

There have certainly been bad times, such as last year when the rains failed altogether. But, even though Machakos's population has risen a staggering fivefold since the 1930s, most years these hills are greener, less eroded and far more productive today than before. Farm output per hectare is ten times what it was in the 1930s and five times what it was in the 1960s. There are, on average, 34 trees per hectare, more than for a century or more. And with tens of thousands of kilometres of terraces dug on steep hillsides, erosion rates are probably also at an all-time low.

What are they doing right? According to Michael Mortimore, a British geographer with long experience in Africa who has written a book on Machakos, the Akamba responded to the environmental crisis by switching from herding cattle to seftled fanning. This gave them the incentive-and their rising population gave them the labour-to work the land properly, digging terraces and collecting water in ponds for irrigation and weed control.

Every farmer seems to have his or her own story of innovation. On the road out of Machakos town, for example, I dropped in on Jane Ngei, who used an ox plough, spade and wheelbarrow to dig her own small dam to collect rainwater running down the road past her farm. With bucket and perforated hose, she uses the water to irrigate a couple of hectares of vegetables, maize and fruit trees that she grows beside her fields. The Akamba farmers are reaping the rewards of improvements like these, selling vegetables and milk to Nairobi, mangoes and oranges to the Middle East, green beans to Britain and avocados to France.

Machakos district, recently renamed Makueni, is just a couple of hours drive from Nairobi, home of the UN Environment Programme, which still maps much of the district as on the verge of desertification. Yet, strangely, it has never sent anyone to research the reality. LJNEP's Timo Maukonen says he believes the main reason for the Machakos success story is the proximity of a large market, Nairobi, for the farmers' produce. Tom Slaymaker of Britain's Overseas Development Institute agrees. He stands by his claim in a recent study that "there are few examples of reversal of natural resource degradation and no evidence of a wider trend of environmental recovery." He insists that "successful cases seem to be rather isolated.'

But other experts are taking a more cautious line and question the value of sweeping claims of elivironmental decline made by UNEP and other UN agencies. Camilla Toulmin, head of the drylands programme of the International Institute for Environment and Development in London and a leading drafter of the Desertification Convention, admits that "evidence for soil fertility decline stems from a few highly influential studies of land degradation in Africa, which have been quoted over and over again, in the process often losing much of the qualification surrounding the original study." Much of it, she says, doesn't stand up to detailed investigation on the ground. 'Detailed field-level studies demonstrate that the soil fertility problem is far more complex and diverse."

One problem has been that researchers tend to visit such areas so rarely that they have little history to back up their guesses about environmental processes. Land that appears 'degraded'-that is, highly eroded-may have been that way long before the arrival of farming or grazing. "Every piece of degraded land has been seen as evidence of destructive human activity," says Niemeijer. 'But when we asked farmers about areas of degraded land near their villages, they generally said it had been there a long time and was a natural feature. And in some cases they were starting to reclaim these areas for farming.'

Deserts did advance in Africa during the droughts of the 1970s and 1980s. The conventional view at the time was that farmers, at least as much as drought, were to blame, and that the processes were irreversible. But even when, in the early 1990s, satellite images began to show the Sahara retreating during years of higher rainfall, the image of desertification caused by human activity stuck. It became what Mortimore calls an 'institutional fact', too important for careers and reputations to be lightly dropped. And it is only now that detailed evidence of what has happened to soils and farm productivity in these supposedly doomed regions is finally emerging. The myth of traditional African farmers as both environmental villains and victims is finally being exposed.

The truth is not that farmers never destroy soils, nor that deserts never advance, but that there is nothing inevitable about the process-it may be the exception rather than the rule. And even when soils have been in decline, as in Machakos, farmers have shown themselves quite capable of turning the tide. Moreover, it seems that even the rapid growth of population in many African countries can be a spur to change, rather than a curse. As Singh puts it: "There is no reason why Africa cannot feed itself." El