The mystery of why farm children have far fewer allergies may have been solved. For years scientists have speculated that something in the rural environment protects against allergies such as hay fever, asthma and eczema, with some research showing the risk is half that of someone living in a city. But exactly what is responsible for such an effect has not been tracked down.

Now scientists have discovered that the answer lies in the cowshed and, in particular, in two strains of bacteria, Acinetobacter lwoffiiand Lactococcus lactis. When they made the bacteria into nose drops and gave them to laboratory animals, they were immediately protected from allergies. Now the aim is to develop a human version of the drops, which could be the first preventive treatment for the growing problem of allergies. “This is the first research to suggest that the use of cowshed bacteria can protect against allergy,” says Professor Otto Holst, one of the international team who made the breakthrough, which was published in the Journal of Allergy and Clinical Immunology.

There has been an increase in allergies, asthma, hay fever and some forms of eczema in the past two to three decades. It has been estimated that 5.1 million people – one adult in 13 and one child in eight – are being treated for asthma and that 18 million people may develop an allergy at some point in their lives. Allergic reactions are caused by the immune system becoming hyper-sensitive to everyday things such as pollen, dust and to certain foods.

A number of theories have been put forward to explain the rise: for example, a health immune system needs to be exposed in early life to bacteria, infections and other potential problems. If this doesn’t happen, later exposure may result in allergies, especially where there is genetic predisposition. In effect, exposure to bacteria and infections helps to calibrate naive immune systems. The new research comes in the wake of more than 20 studies all of which have indicated that children brought up on farms have low levels of allergy, hay fever and asthma. But while they established a link, they did not track down what was responsible.

Cowsheds were chosen because of the abundance of bacteria. Over time the team collected several kilos of dust and many bacterial species from the floors of German, Swiss and Austrian cowsheds. To make the task manageable, they

analysed blood samples of farming children to see whether they had come into contact with any particular bugs that nonfarming kids hadn’t. Having isolated the bacteria, the scientists then converted them into nose drops, which they found protected mice from allergies.

The team members are now looking at developing a drug that can treat allergies in human beings, especially one that can be given to children to prevent them becoming allergic or asthmatic in the first place.

There are also investigating whether people who live in villages and small towns also enjoy the bacteria’s protective benefits, as the strains get carried from the cowshed farther afield, on tractors and by farmworkers.

Here are some of the other theories that may explain the rise in allergy cases.

DIET

Several studies have suggested that changes in diet in recent years may play a significant role in the rise in allergies, asthma and hay fever. A study at King Abdulaziz University, in Saudi Arabia, found that eating at fast food outlets, a low intake of milk and vegetables and of fibre, vitamin E, calcium, magnesium, sodium and potassium. were all significant risk factors for wheezy illness. A study at the University of Crete looked at diet in rural Crete, where wheezing and hay fever are rare, and found that children who ate a lot of fruit and vegetables were 65 per cent less likely to have hay fever. Nuts also lowered the risk; margarine increased it.

SWIMMING POOLS

When researchers from National Research Center for Environment and Health, in Germany, looked into the childhood background of adult hay fever sufferers, they discovered that they were much more likely to have used swimming pools than other men and women. The team investigated 2,606 adults, aged 35 to 74, and found that those who used pools regularly as a child were 74 per cent more likely to develop hay fever, and the greater the use, the bigger the risk. The researchers suggest that chlorine has an effect on the lung lining, allowing closer contact with allergens such as pollen.

OBESITY

Research findings at Ludwig-Maximilians-University of Munich indicate that when people brought up on farms are obese, their risk of hay fever and allergies rises.

The study, based on nearly 2,000 German adults , shows that, overall, those brought up on farms had a 40 per cent lower risk of hay fever and allergies. But they found that among obese people all the protective effect was lost. “The high prevalence of respiratory allergies in inner-city societies might be explained by obesity,” the researchers say.

WATER

Drinking purified water may increase the risk of allergic diseases because beneficial microorganisms, which prime the growing immune system, have been removed. In one study, researchers from Helsinki University Central Hospital found that in Russian Karelia, where allergic diseases are rare, lakes and rivers are widely used for domestic water, often without any chemical or other treatment. A study in Ethiopia also showed that drinking river water in rural areas protected against eczema.

LAZY KIDS

The rise in hay fever, allergies and asthma has coincided with a decline in physical activity, and research at the Institute of Epidemiology, Neuherberg, Germany, suggests that they may

be linked. The researchers, who investigated 2,400 children, found that the prevalence of hay fever was 2.4 times higher in inactive children, and the risk varied with the level of activity, suggesting that the link was not coincidence. “Although the underlying biological mechanisms could not be clarified, increasing physical activity in childhood is suggested to prevent hay fever,’’ the researchers say.

CLIMATE

A number of studies have suggested links between climate, especially the increase in global temperatures, and the rise of allergies and asthma. A study at the University of Verona of 18,000 people found that the Mediterranean climate was associated with a 23 per cent increased risk of wheeze, and a 19 per cent rise in asthma attacks.

Some research suggests that prevalence may rise with climate change. A study in Switzerland suggests that in some areas, the pollen of birch trees is about three weeks earlier than 20 years ago. Another indication is that the unseasonable hot weather earlier this year triggered a doubling of calls to NHS Direct from people with eye problems related to hay fever.

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