Bb is king

Arno Karlen's last book, Plague's Progress: A Social History of Man and Disease, found him grouped, in some eyes, with the darkest spirits among eco-doomsters: those who see infectious epidemics as the ultimate, perhaps even necessary, control on human population. His new offering is only moderately sinister, and that in a laid-back, often witty way. The Biography of a Germ sneaks up on its subject with great ease, charm and sense of timing. His story is ultimately highly dramatic, with especial resonance for the thousands of affluent suburbanites who live among the deer-haunted woodlands of the north-east United States. In Connecticut, in particular, the pretty colonial town of Lyme has given its name to a disease which is inflicting considerable regional harm, and is increasing and spreading in the Old World as well.

With a teacher's feel for revelation, Karlen saves his sensations for the end. He wants us first to learn, with proper awe, about bacteria and how they fit into the community of life; their anatomy, lifestyle and reproduction and how very, very small they are. To inspect his chosen species, one needs an electron microscope, and then, to study one of its flagella is "like scrutinizing one hair on the head of someone in another town".

The species is Borrelia burgdorferi, a silvery corkscrew of a spirochaete, a shapeshifting survivor of incredible journeys, a blood-traveller armed with all manner of devices against eviction by mammalian immune systems. In the course of one's lifetime, a thousand or so microbial species become one's constant companions, but Bb (as one comes to know it) is a lodger that can leave its human hosts chronically feverish, arthritic and exhausted.

The "natural" progress of its infectious life is remarkable, beginning in a woodland mouse, continuing, say, in a raccoon or hedgehog, and ending up in a deer, to none of which it does much harm. Its carrier between mammals is, however, a blood-feeding tick - in America, the deer tick, Ixodes scapularis; in Ireland and Europe, its counterpart, I. rici- nus, the sheep tick. When the ticks bite people (or even cattle or dogs) whose immune system is vulnerable, the Bb delivered in saliva can set off a whole syndrome of symptoms: swollen joints, recurring fever and flulike misery.

If Bb has been lurking in the undergrowth since year dot, why the sudden epidemic of a "mystery" disease only 25 years ago? Karlen traces ecological and land-use changes that could have almost extinguished the bacterium and then given it a fresh lease of life. New leafy suburbs have pressed out into woods growing up on abandoned farmland; newly-indulged deer now wander across the lawns of nature-loving city commuters.

Karlen is unexpectedly impatient of the "Arcadian fantasy" which resists deer-culling and insecticide-spraying or even wearing tick-repellents; his book may change some minds. But its lasting worth is as a compelling piece of natural history of (almost) the smallest lives on earth.

Michael Viney is an author and an Irish Times columnist