Mystery twists in horror story

It is indisputable that interest in the rare and unusual greatly exceeds that given to the common and mundane. The appearance of yet another book on transmissible spongiform encephalopathies (TSEs) should not therefore be surprising because, by any criterion, the number of human victims of these diseases remains exceedingly small. CJD and variant-CJD are terms that carry meaning for most of us, even if their uncommonness dictates that the vast majority of doctors will never see a case during their professional lifetimes. Rarity does indeed have something to do with this - like the value of an old book being inversely proportional to the number of copies printed - but not a lot. Public interest is nearly all a consequence of the nature of the diseases, and their impact on political processes and politicians.

Top of the list is how lethal these diseases are. In modern times, the notion of a transmissible disease with 100 per cent mortality unaffected by treatments routine or even experimental is dreadful, shocking and unacceptable. It is worse in v-CJD cases because nearly all its victims are young and because they take a long time to die. Horror is further compounded because the causative agent attacks the brain. It targets and destroys the personality and vitality of its victims before it kills them.

All this would be more than enough to bring these diseases to public attention and induce the funders of research and scientists to take a particular interest in them.

But, of course, there is a lot more. Their transmission has been linked to cannibalism. The type of agent that causes them is equally unusual in that it is neither a bacterium nor a virus; its composition may be unique in lacking nucleic acid. A majority of workers in the field believe that a protein (or proteins) is sufficient. The scientific consensus on this is not universal, however. The agent has neither been purified to molecular homogeneity nor synthesised in infectious form in the test tube (such as poliovirus), leaving room for a minority who think that a small nucleic acid is the key molecule.

The controversy and the fact that unusual biological principles may be at work makes the subject noteworthy. It also illustrates science in action in rather dramatic fashion and reminds us that TSE science itself is particularly difficult. For example, because the incubation period of the diseases is very long, experiments take a long time.

It is fortunate that many of the doctors and scientists who have worked on them have been clever, persistent and original. Many have had personalities and traits as distinctive and unusual as the subject they have chosen to study. Creutzfeld himself was an anti-Nazi professor in Kiel from the mid-1920s onwards. The Gestapo took an interest in him because he transmitted his views to those he taught, a very dangerous thing at a time when the universities in the Third Reich were falling into darkness aided by their professoriat - particularly medics - and their students.

Two US scientists in the field have won the Nobel prize, Stanley Prusiner, who coined the term "prion" - proteinaceous infectious particle - and advocate of the protein-only hypothesis, and the unconventional Carleton Gadjusek, who worked on kuru, the disease spread by cannibalism, and showed that CJD could be transmitted to animals. His unconventionality extended to his sex life; two decades after winning the prize he served a year in prison for paedophilia.

In Britain we have had our own home-grown drama. BSE is another abbreviation that needs no spelling out, and the story needs no repetition.

Victims were and are not only those young people infected with it, but the beef industry and the taxpayer (more than £400 million is being spent on control measures). After a decade of reassurance, the announcement in the House of Commons at 3.31pm on March 20 1996 of a possible link between BSE and v-CJD had a near-lethal effect on trust in the government, in experts and in science.

All this suggests that writing a book about TSEs should be easy. How was it for Philip Yam? In The Pathological Protein: Mad Cow, Chronic Wasting and Other Deadly Prion Diseases , he does a good job. He mixes science and human interest with skill. Since he is news editor of Scientific American it is not surprising that his accounts of technical matters are reader-friendly, but do not dumb down.

Books on TSEs are appearing at regular intervals. What added value does Yam's provide? It is comprehensive, well researched and well referenced.

But its main merit for UK readers is that it covers the subject from an American perspective, even if this has encouraged the occasional error to creep in. Two of the 14 chapters - which detail how the authorities have acted to protect the US food supply from prions, and the chronic wasting disease of deer and elk - focus exclusively on North America. It is a common complaint that scientific books and papers written by Americans are excessively parochial. References to work outside the US are unfairly sparse, even if it has to be admitted that the hegemony enjoyed by the US in science, as in other spheres of activity, justifies this kind of behaviour in substantial degree. Yam's book cannot be criticised on these grounds. Its coverage is balanced and international.

Hugh Pennington is professor of bacteriology, University of Aberdeen.