Millennium Bugs With A Deadly Bite - disrupting ecosystem can lead to disease outbreaks

Through an arrogant or ignorant disregard for ecological complexities, ceaseless human encroachment on nature can unleash a terrible new threat of killer diseases carried by microbes that have long lain undisturbed

At first, the men seemed to be suffering from nothing more than a case of influenza: a bad headache, aching joints, a fever. But it quickly became clear that dozens of Durba's gold miners in the Democratic Republic of the Congo were in the grip of something far worse. Somehow, late last year, they had come into contact with a terrifying infectious agent that was attacking all their internal organs, causing them to bleed uncontrollably.

Over the following months, over 60 miners died from the mystery disease, their limp bodies covered with blotches and oozing blood even after death. Local doctors had never seen anything like it. At first, not even seasoned experts from the World Health Organization (WHO) could say for sure what was causing such appalling deaths.

But many harboured the same suspicion: that the miners had become infected by a so-called emerging virus: a tiny packet of genes that had lain undisturbed in its natural lair for years, perhaps millennia - until humankind blundered into it.

The suspicion was that the mystery disease was caused by a so-called filovirus, a thread-like virus whose devastating effect on the human body had first been discovered 30 years ago.

In 1967, dozens of people working in laboratories in Germany and Yugoslavia fell ill with eerily similar symptoms. Seven died, and many of the survivors suffered long-term effects ranging from impotence to insanity. The source of the infection was traced to a batch of vervet monkeys imported from Uganda, many of which had died during transportation.

The monkeys were found to be carrying a filovirus, which was duly named after one of the German towns where the first cases emerged: Marburg. To this day, no cure has been found. If the victim's immune system cannot fight it, it's over - a fate that awaits over 50 per cent of those who become infected.

Deadly pathogens-do not disturb

In May, WHO confirmed everyone's fears: tests on blood samples taken from the miners showed that they had indeed been infected with Marburg virus. Soon reports began to emerge of an outbreak of the same disease among soldiers in Zimbabwe. Thousands of troops had been crossing into DRC to support President Laurent Desire Kabila as he tried to put down a rebel uprising.

Fortunately, blood tests on three soldiers suspected of carrying Marburg turned out to be negative, and by early summer the outbreak in Durba was over. The virus had vanished again, back into its jungle haunts - but precisely where, no one knows. Somewhere out there, a creature - a species of bat, perhaps, or a rodent - is unwittingly acting as a refuge for Marburg.

What is clear is that the more incursions into virgin territory humankind makes, the greater the risk of another encounter with Marburg - or perhaps something worse. After decades of insouciant use and abuse of the world's natural resources, from the primordial forests of equatorial Africa to the oceans, the threat of disturbing new and deadly pathogens now has to be taken seriously.

The warning signs have long been clear. As long ago as 1485, reports emerged of a disease known as the Sweating Sickness, in which victims progressed from sudden sweating to prostration and death in just 24 hours. It struck four more times before vanishing again in 1551. But the country affected was not some isolated jungle community in the tropics. The Sweating Sickness wreaked its havoc in England, ultimately claiming the lives of around 20,000 people - over 0.5 per cent of the total population.

Recent research has linked the emergence of Sweating Sickness to a strikingly modern phenomenon: deforestation. The timing and spread of the outbreak ties in with the mass destruction of woodland in Shropshire, on the western borders of England. The suspicion is that forest workers somehow allowed the virus responsible for the disease to spread beyond the creature that had acted as its host for countless generations, bringing it into contact with populations big enough to sustain an epidemic.

This is a scenario that has been played out again and again in our own times. In Argentina after the Second World War, vast areas of the Pampas were cleared with herbicide to make way for new crops. In the process, the natural balance between a species of field mouse and its predators was disturbed, and the numbers of the former soared - as did those of itinerant farm-workers. By the early 1950s, people began to fall prey to fevers, vomiting and headache. Some went on to suffer massive haemorrhaging, and died hideous deaths. The cause was eventually traced to a previously unknown virus, Junin, carried by the field mice.

The same story was repeated in Bolivia, where farmers keen to grow maize hacked down stretches of jungle near the Machupo River. Sure enough, the reports of strange, horrible deaths among farm-workers started to roll in, and their cause was traced to another haemorrhagic virus, duly named Machupo, again carried by field mice.

And early in 1999, evidence emerged to link campaigns of deforestation to the rise of the most notorious emergent disease of them all: Aids. In February, an international team of researchers published a paper in the journal Nature that points to the chimpanzee Pan troglodytes troglodytes as the natural host of HIV-1, the lethal virus that now infects over 30 million people worldwide.

Killed for their meat by hunters hired by timber companies, these apes are butchered in their thousands each year in conditions that are ripe for the transmission of viruses. Finding its way into cities via infected meat for restaurants and via the hunters themselves, HIV-1 went on to be sexually transmitted throughout the world, according to this latest research. To date, over 12 million people have died from Aids, 80 per cent of them in sub-Saharan Africa.

The dangers of an arrogant disregard for the complexities of ecosystems may take other forms than the destruction of virgin territory. It was, for example, attempts at reforestation in north-eastern America during the 19th century that led to the recent emergence of Lyme Disease, a potentially fatal bacterial infection affecting the joints, heart and brain, passed to humans via ticks carried by deer.

The deer came into contact with humans following moves to rectify the impact of deforestation caused by intensive farming. Local governments launched preservation and reforestation programmes, and created a landscape attractive to both humans, deer - and Ixodes scapularis, a deerborne tick which carries Borrelia burgdorferi, the bacterium responsible for Lyme Disease.

With few natural predators in the newly-formed ecosystem, the deer flourished, and increasingly came into contact with humans, who were also flocking to the area, entranced by its apparently "natural" beauty. By the mid-1970s the first cases of the tick-borne disease were being noted among the inhabitants of Old Lyme, Connecticut.

The same story has since been played out in Europe, Asia and Australasia, and tens of thousands of cases of Lyme Disease are reported worldwide each year.

The return of TB, diphtheria, cholera and malaria

The return of a number of old killer diseases once thought vanquished also serves to warn of the dangers of hubris and complacency. Tuberculosis, all but eliminated in the West following the advent of decent housing and powerful drugs, has been on the rise again since the mid-1980s with over three million killed each year worldwide. Many experts blame sloppy use of antibiotics by Western doctors, which has allowed mutant TB bacteria to survive and create resistant strains. In developing countries, the Aids epidemic - which has left tens of millions with no disease-fighting immune system - caused the number of TB cases to triple by the early 1990s.

Outbreaks of diphtheria, another bacterial disease of the lungs that especially targets young children, were virtually unknown in the last days of the former Soviet Union. Around 40,000 cases were reported in 1998, primarily among the poor and homeless who flocked to major cities following the collapse of the union, whose health-care systems had collapsed with it.

In the early 1990s, cholera returned to haunt the Americas after a century of absence. Experts suspect this deadly bacterial gut disease was imported from Asia in water flushed from the ballast tanks of ships. At the turn of the century, virtually no cases were known in the Americas; today, around 60,000 cases are being reported each year. Globalization of commerce has, it seems, given us all too ready access to rather more than just exotic produce from faraway lands.

Yet of all the resurgent diseases, it is malaria that provides the most poignant example of where ecological effects have shattered the dream of complete eradication. The original optimism stemmed from the introduction of DDT into developing nations, to kill off the mosquitoes that carry the parasite responsible for malaria.

Within ten years of its introduction after the Second World War, DDT had saved an estimated 5 million lives. In many countries, the impact was truly astonishing. In 1948 Sri Lanka had 2.8 million cases of malaria; by 1963, following the introduction of DDT, the number had fallen to just 17.

But by the late 1950s, evidence had emerged suggesting that DDT's persistence in the soil and ability to creep up the food chain was having a deadly effect on some forms of wildlife.

Although some experts are beginning to dispute the evidence - and especially its relevance to the Third World - DDT now faces a worldwide ban. The mosquitoes have, however, gone from strength to strength. In Sri Lanka, the number of malaria cases rose from 17 back to 2.5 million within just five years of abandoning DDT. Worldwide, a staggering 400 million cases are being reported each year, along with almost two million deaths - 90 per cent of which take place in Africa.

In March 1999, Dr Gro Harlem Brundtland, the Director-General of WHO, singled out malaria as an example of a pandemic killer likely to benefit from another environmental threat: global warming, caused by man-made pollution trapping more of the sun's heat in the atmosphere.

Dr Brundtland pointed out that malaria is now being reported in locations at higher altitudes than in previous years, such as the mountain plateaus of Kenya. While admitting that there are likely to be various explanations for the change, Dr Brundtland believes that one possibility is global warming.

Rising sea-levels, caused largely by the thermal expansion of water driven by global warming, pose another threat, according to Dr Brundtland. "If coastal protection systems are not strengthened, a 50-centimetre rise in sea-level by 2100 would place 80 million people in danger of being flooded more than once a year, compared to 46 million people under present climate and sea-level conditions," she says. "The displacement of so many people to already densely-populated delta areas and on populous island states would be bound to result in outbreaks of diseases like diphtheria and diarrhoea, just to mention the most obvious ones. The rising water table along the coast could also encourage the release of pathogens into septic systems and waterways."

But while the effects of global warming on sea levels have yet to make themselves clear, fears are already growing that the sea may pose a more immediate - and insidious - threat to health.

It stems from humankind's insouciant use of the world's oceans as gigantic sewers. A 1993 World Bank report estimated that around 30 per cent of humans have no other waste disposal system than streams, rivers - and the sea.

For years a case of"out of sight, out of mind", the dumping of so much waste in coastal waters is now starting to have an impact on health. Viruses from human diseases like polio and hepatitis have started to be found in shellfish, while toxic algal blooms - vast colonies of simple, pathogen-packed organisms that thrive on waste-derived nutrient - are becoming increasingly frequent along coastlines.

It is now becoming clear that the sea is acting like a gigantic cold-store for potentially deadly microbes like rotavirus, responsible for severe diarrhoea, and poliovirus - and sometimes they emerge to cause havoc on the mainland. In December 1992, thousands of people in Bangladesh fell victim to cholera, following an upwelling of bacteria-laden ocean water off the southern coast.

From deforestation to overpopulation, mass migrations to global transport, atmospheric to oceanic pollution: the reasons for which new and resurgent diseases can and do rise up to threaten humanity are legion. But lessons are being learned. Some are very basic and relatively simple to implement, such as the one-time-only use of hypodermic needles. Others are equally obvious but far harder to achieve, such as making safe sex advice effective among those at risk from sexually-transmitted diseases like Aids.

Early detection and rapid control measures

As with any threat, eternal vigilance for new disease outbreaks is now being seen as crucial. In its report on the outbreak of plague in India in August 1994, the All-India Institute of Medical Sciences warned that such re-emerging infectious diseases are a growing threat world-wide. "Early detection and rapid implementation of effective control measures are essential," the report's authors said, and duly called for the setting up of national surveillance centres to act as early-warning systems.

But the key message now emerging from many of the recent outbreaks is a blunt one: we must become far more thoughtful in our dealings with the environment and its delicate ecosystems. Long dismissed by some as just a pious desideratum, the cost of ignoring this simple message could be nothing less than the needless death of millions.

Robert Matthews, Science Correspondent of the Sunday Telegraph, London

COPYRIGHT 1999 UNESCO
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