Study shows rural link in hay fever

By MARTIN JOHNSTON

Farm children are more than twice as likely to suffer hay fever as youngsters in towns, a New Zealand study of allergies has concluded.

The study of 293 children aged 7 to 10 in the southern Hawkes Bay will be published in the European journal Allergy this month.

The Wellington Asthma Research Group found that 29 per cent of the children on farms had hay fever, compared with 14 per cent in towns.

The researchers say that, despite appearances, the study does not disprove the widely held "hygiene hypothesis".

This theory suggests that as life in the West has become more hygienic and the rate of childhood infections has declined, people's immune systems have become allergic to otherwise harmless substances like minute dust-mite faeces.

Allergic diseases include hay fever, eczema and most asthma cases.

As well as asking about hay fever, the researchers checked eczema and current wheezing, and conducted skin-prick tests for allergies to eight common allergens.

"The only one of those that's statistically significant is hay fever," said the Otago University research group director Professor Julian Crane.

"But the others are tending to go the same way, suggesting there's more of a problem on the farm.

"It is the first study in New Zealand specifically to look at farm exposures and allergic disease.

"It suggests - in contrast to findings on some European farms - that allergic disease is more common among farming families than non-farming.

"However, it also suggests that specific early animal exposures such as to pigs, or consuming yoghurt or unpasteurised milk, provide some protection."

Dust was collected from the participants' living room floors and checked for the level of endotoxin, a substance that forms part of the cell wall of certain bacteria found in animal faeces.

On average, samples from town homes had nearly 50 per cent more endotoxin per gram of dust than those from farm houses.

Professor Crane said while comparisons with European endotoxin levels were not yet possible because of differing scientific techniques, the Hawkes Bay study suggested that with "less of the farmyard" getting inside farmhouses than town homes, there was less protection from allergies.

"This doesn't disprove the hygiene hypothesis. It just shows that things are different on New Zealand farms."

European farms tended to be much smaller and the whole family usually had much closer contact with the animals, which were often brought underneath the house during winter.

The Hawkes Bay study also found that children exposed early in life to cats were less likely to experience hay fever, and those exposed to dogs early on were less likely to have asthma.

Massey University is also testing the hygiene hypothesis. In a three-year study in the lower North Island, researchers are comparing 3000 families who live on farms with 1000 in cities and towns.

Herald feature: Health