Letter: Vegetarians and CJD

Sir: Science progresses by learning from the unexpected. The report that an unfortunate young woman has contracted new variant CJD though she had been for many years strictly vegetarian, suggests a rethink about the mode of entry of the infecting agent (part of a protein).

A hint lies in a small paragraph in the report which stated that the lady worked in a pet-shop and regularly handled dry pellet dog food. Any new hypothesis should include this new fact. Dry dog food, like the dry supplementary feed which is given to cows to increase the milk yield, is potentially dusty stuff. Animals snuffling through the food in a feeding bowl obviously inhale some.

Could this have been the mode of `infection' with the prion protein, not only for cows and other domesticated animals, but for human handlers of the food?

At first sight the respiratory tract is not a likely route of entry; apart, that is, from the nose, where the sensory apparatus for smell lies.

This consists of nerve cells whose processes protrude at the surface of the mucous membrane where they pick up smell particles.

These nerve cells derive from and remain in direct contact with the brain. Here is a relatively easy point of entry to the brain by infected dust.

Several features support this idea in humans. Firstly, the unexpectedly short incubation time in cases of the new variant disease. This was found experimentally in many species when direct brain implantation by the agent was made as opposed to giving it in food.

Secondly, the relative youth of the known cases. The sense of smell is not human's strongest. It deteriorates as we age, and the relevant nerve cells in the nose are reduced in numbers by middle age: in many older people they have been lost completely, together with the sense of smell.

Could this be the reason why the elderly have not so far shown the `new variant' disease? Only fairly young people with good olfactory systems have so far been affected.

Has the restriction of beef from our diets been an unnecessary result of a faulty hypothesis?

Peter Yates

Emeritus Professor of Neuropathology

Beach House

Silverdale, Lancashire