BUGS ON THE MOVE

Many diverse factors affect the spread of disease. Roger Dobson reports on a new book charting the medical geography of Britain
Click to follow
The Independent Culture
Almost exactly 170 years ago, in a small town on the Ganges, an outbreak of cholera claimed its first victim. Two months later the disease had been swept along the merchants' roads of the day to the Punjab, then on to Afghanistan, and across to Persia following the international trade routes. Three years later in 1830 it hit Odessa and then Moscow. In August of the following year it was killing people in Berlin and two months later the first case was reported in Hamburg.

On 19 October, 1831, four years after the first cases on the Ganges, cholera arrived in Britain with the first reported patient in Sunderland. Within a year it had spread to most towns and cities in the country with a final death toll of more than 50,000.

The tracking of the Great Ganges Cholera epidemic of 1827, its advance along the trade routes and the concentration of victims in cities and towns, gives a graphic insight into the geography of disease. It also underlines the importance of social and environmental factors in the spread, devastation and human suffering caused by diseases down the centuries like bubonic plague, pestilence, smallpox, cholera, polio, typhoid, and TB.

And today's biggest killers, including heart disease, obesity, respiratory problems, and many cancers, as well as conditions like asthma and allergies, have their origins in the environment too.

But in the international quest to map the human genome and the search for genetic explanations and gene-based therapies, social and environment effects in modern disease have been overlooked.

Professor Melvyn Howe has put nurture firmly back on the agenda with a major research work published this month which underlines just how much disease and death are a lottery depending on how and where people live and work.

Although the onset and progress of some diseases is dictated by our genes, in most cases the genes we are born with predispose us to certain conditions and disorders, and it is largely lifestyle which determines which ones get activated.

"Disease is essentially a reaction between individuals and the stresses and adverse factors of their physical, biological and social milieu, and how we respond is governed by genetic make-up," says Professor Howe, emeritus professor of geography at Glasgow University, fellow of the Royal Geographic Society, and world authority on the science of medical geography.

Diverse factors are implicated in disease: the water we drink, time spent commuting, housing and working conditions, beaches we visit, migration, blood group, annual fog amounts, volume and temperature of rain, diet, radiation, ozone levels.

Geographical and social differences explain significant differences in the health and disease profile of different parts of the country. And as Professor Howe's research shows, there has been cause and effect ever since man swapped the countryside for the cave and became warmer, but was also exposed to different kinds of bugs.

"In Britain there is no longer a poor, rural pop-ulation exposed to the killing diseases of infancy and childhood, but our urbanised society is scourged by modern epidemics of diseases of the cardiovascular and respiratory systems, by cancers and mental illness," says Professor Howe.

"From the evidence and with the benefit of hindsight it is clear that aspects of the environment continue to have a profound influence on human health and well-being," says Professor Howe.

"People are living longer and enjoying healthier bodies than ever before. But whereas major disease problems were once acute illnesses with an abrupt onset and finite duration, the major ones now are chronic illnesses of infinite duration."

Each phase of development has brought with it a new or more virulent disease. Solving the problems of meat supply through the domestication of animals, for instance, led to smallpox, helminthic disease and possibly TB, while solving the problem of food storage and advanced civilisation led to towns and cities, and to plagues and the rapid spread of infectious diseases.

But the spread and penetration of disease is not uniform. Two hundred years ago, trading ports like London, Bristol and Liverpool were hit first as ships carrying infected rats, infested cargoes and diseased sailors arrived in ports.

Bubonic plague, for example, arrived in Britain through Weymouth in August 1348 and spread along the commercial routes of the country. By 15 August it was in Bristol and within six weeks the disease had arrived in London.

Major changes came with the industrial revolution. Until then, the population had been largely rural and static, but industrialisation brought mobility and with urbanisation came overcrowding, insanitary conditions and disease. At the turn of the century TB accounted for one in 10 deaths, almost three times the death toll from cancer.

Migration also mixed race and genes. The distribution of different populations over the last 3,000 years have become blurred by movement and inter marriage, but the differing frequencies of blood groups around the country give important clues.

High concentration of people with blood group O occur, for instance, found in Scotland and North Wales, may indicate characteristics of Neolithic and later prehistoric settlers who came to Britain by western sea routes. In parts of Scotland, more than 60 per cent of the population is group O, compared to less that 40 per cent in southern Britain.

Similarly, higher rates of blood group O in southern Britain may be linked to Anglo Saxon and Viking invaders. Blood group AB is five times more common in western Britain than the east.

Blood groups not only produce an insight into historical migration patterns, they are important indicators of disease, too. People with group O, for example, are 40 per cent more likely to get a peptic ulcer, while cancer of the stomach is 25 per cent more common in those with group A.

Throughout this century, improvements in public health, housing and education brought many diseases under control. But as we approach the millennium, there are still substantial geographic differences in health in Britain.

"In large towns people live in a polluted at- mosphere to which their lungs respond with respiratory disorders and cancerous growth. Overcrowding assists the spread of droplet infection," points out Professor Howe.

Our life span has increased dramatically since prehistoric man who died at around 18, but there are still significant variations across the country. In England and Wales the average age people can expect to live is 75 for men and 79 for women, but in Scotland men die four years younger and the average age of death for women is 77.

What may be responsible for regional differences is a combination of factors. The weather - wind, rain, humidity, temperature and negative ions - almost certainly plays a part.

"There are probably few diseases whose distribution is not affected by climate. In part, climate determines foods eaten, quality of sanitary methods and appliances, the structure of homes, offices and factories, the viability of micro-organisms outside the body - and the insects which carry these micro-organisms," says Professor Howe.

Wet and damp weather, for example, is associated with rheumatic diseases and the extreme west of the UK gets on average 250 rainy days a year compared to less than 175 in parts of East Anglia.

Sunshine not only provides vitamin D, it also increases the sensation of good health, and those living on the south coast get far more of it than the rest of the country. Cornwall around to East Anglia, gets more than five hours a day on average, compared to less than three hours a day in the west of Scotland.

Fog is a known killer - 4,000 people died in the 1952 London smog. In the 1950s, London lost an average 44 minutes a day of bright sunshine due to smog, while the duration of sunshine in cities like Leeds, Sheffield and Glasgow was half that of the outlying areas in winter months.

The visible pollution which caused these smogs has now largely gone, thanks mainly to the Clean Air Act of 1956, but many urban areas are now surrounded by clouds of invisible gases - carbon monoxide, nitrogen oxide and sulphur dioxide.

The spread of some modern health problems can be traced as accurately as the Ganges cholera outbreak. Modern shopping and living habits - cooking food too quickly and not re-heating food at high enough temperatures to kill bacteria are implicated in current epidemic of food poisoning with reported cases increasing four fold in a decade.

The international and cross-country distri- bution of food means that microbes which once survived only in local produce have become widespread, and diseases and bacteria can now spread as fast as food is distributed.

Some of the geographic links in disease are less obvious. The valleys of south Wales, for instance, have high rates for many illnesses, but also have a comparatively low rate of deaths from lung cancer. For many years researchers looked for clues as to why this should be so.

They now believe that the reason may well be that until the mid 1980s, the valleys were one of the power houses of Britain, producing huge amount of coal from deep mines, and the thousands of miners who worked there were not allowed to smoke underground because of the fear of triggering off gas explosions. The ban meant that the men had to spend more than half their waking life without a cigarette.

Ironically, the conditions which reduced the risk of lung cancer for the miners, also exposed them to coal dust and pneumoconiosis.

On the whole, according to the research, the healthiest areas to live are in the south and east of England, but in many urban areas stress is implicated in ill health. People living in dense housing estates in inner cities suffer with high rates of unemployment and long-term illness, and are also exposed to social tension. For many commuters the health benefits of a short working day are negated by the hours they spend travelling to work which increases irritability and anxiety and interrupts the harmony of family life.

Health education campaigns are under way to try and change lifestyles, but the incidence of obesity is still increasing and reaching epidemic proportions, lung cancer deaths among women are going and, in some areas, are poised to replace breast cancer as the number one killer of women.

And while these threats of today are being tackled, the next generation of diseases may already be looming. More and more bacteria are becoming resistant to antibiotics, killer viruses like Ebola and Dengue Fever are emerging from the Third World, and Britain's population of rats, the notorious carriers of disease, has increased by 30 per cent in a decade to 60 million.

The Ganges cholera epidemic of 1827 took nearly five years to reach Britain as traders meandered along the old trade routes. With modern jet travel, tomorrow's viruses and infections will be arriving much more quickly.

! 'People, Environment, Disease and Death' by G Melvyn Howe, University of Wales Press, pounds 50

Comments