Моральный вирусолог

 "You take precautions, I suppose."

 She smiled, but kept her eyes closed. "Damn right I do. If a man won't wear a condom, he can take his business elsewhere. And I put it on, he doesn't do it himself. When I put it on, it stays on. Why, have you changed your mind?"

 "No. Just curious."

 Shawcross always paid in full, in advance, for the act he did not perform, and always explained to the woman, very clearly at the start, that at any time he might weaken, he might make the decision to rise from the chair and join her. No mere circumstantial impediment could take any credit for his inaction; nothing but his own free will stood between him and mortal sin.

 Tonight, he wondered why he continued. The "temptation" had become a formal ritual, with no doubt whatsoever as to the outcome.

 No doubt? Surely that was pride speaking, his wiliest and most persistent enemy. Every man and woman forever trod the edge of a precipice over the inferno, at risk more than ever of falling to those hungry flames when he or she least believed it possible.

 Shawcross stood and walked over to the woman. Without hesitation, he placed one hand on her ankle. She opened her eyes and sat up, regarding him with amusement, then took hold of his wrist and began to drag his hand along her leg, pressing it hard against the warm, smooth skin.

 Just above the knee, he began to panic - but it wasn't until his fingers struck moisture that he pulled free with a strangled mewling sound, and staggered back to the chair, breathless and shaking.

 That was more like it.

The Shawcross virus was to be a masterful piece of biological clockwork (the likes of which William Paley could never have imagined - and which no godless evolutionist would dare attribute to the "blind watchmaker" of chance). Its single strand of RNA would describe, not one, but four potential organisms.

 Shawcross virus A, SVA, the "anonymous" form, would be highly infectious, but utterly benign. It would reproduce within a variety of host cells in the skin and mucous membranes, without causing the least disruption to normal cellular functions. Its protein coat had been designed so that every exposed site mimicked some portion of a naturally occurring human protein; the immune system, being necessarily blind to these substances (to avoid attacking the body itself), would be equally blind to the invader.

 Small numbers of SVA would make their way into the blood stream, infecting T-lymphocytes, and triggering stage two of the virus's genetic program. A system of enzymes would make RNA copies of hundreds of genes from every chromosome of the host cell's DNA, and these copies would then be incorporated into the virus itself. So, the next generation of the virus would carry with it, in effect, a genetic fingerprint of the host in which it had come into being.

 Shawcross called this second form SVC, the C standing for "customised" (since every individual's unique genetic profile would give rise to a unique strain of SVC), or "celibate" (because, in a celibate person, only SVA and SVC would be present).

 SVC would be able to survive only in blood, semen and vaginal fluids. Like SVA, it would be immunologically invisible, but with an added twist: its choice of camouflage would vary wildly from person to person, so that even if its disguise was imperfect, and antibodies to a dozen (or a hundred, or a thousand) particular strains could be produced, universal vaccination would remain impossible.

 Like SVA, it would not alter the function of its hosts - with one minor exception. When infecting cells in the vaginal mucous membrane, the prostate, or the seminiferous epithelium, it would cause the manufacture and secretion from these cells of several dozen enzymes specifically designed to degrade varieties of rubber. The holes created by a brief exposure would be invisibly small - but from a viral point of view, they'd be enormous.

 Upon reinfecting T-cells, SVC would be capable of making an "informed decision" as to what the next generation would be. Like SVA, it would create a genetic fingerprint of its host cell. It would then compare this with its stored, ancestral copy. If the two fingerprints were identical - proving that the customised strain had remained within the body in which it had begun - its daughters would be, simply, more SVC.

 However, if the fingerprints failed to match, implying that the strain had now crossed into another person's body (and if gender-specific markers showed that the two hosts were not of the same sex), the daughter virus would be a third variety, SVM, containing both fingerprints. The M stood for "monogamous", or "marriage certificate". Shawcross, a great romantic, found it almost unbearably sweet to think of two people's love for each other being expressed in this way, deep down at the subcellular level, and of man and wife, by the very act of making love, signing a contract of faithfulness until death, literally in their own blood.

 SVM would be, externally, much like SVC. Of course, when it infected a T-cell it would check the host's fingerprint against both stored copies, and if either one matched, all would be well, and more SVM would be produced.

 Shawcross called the fourth form of the virus SVD. It could arise in two ways; from SVC directly, when the gender markers implied that a homosexual act had taken place, or from SVM, when the detection of a third genetic fingerprint suggested that the molecular marriage contract had been violated.

 SVD forced its host cells to secrete enzymes that catalysed the disintegration of vital structural proteins in blood vessel walls. Sufferers from an SVD infection would undergo massive haemorrhaging all over their body. Shawcross had found that mice died within two or three minutes of an injection of pre-infected lymphocytes, and rabbits within five or six minutes; the timing varied slightly, depending on the choice of injection site.

 SVD was designed so that its protein coat would degrade in air, or in solutions outside a narrow range of temperature and pH, and its RNA alone was non-infectious. Catching SVD from a dying victim would be almost impossible. Because of the swiftness of death, an adulterer would have no time to infect their innocent spouse. The widow or widower would, of course, be sentenced to a life of celibacy, but Shawcross did not think this too harsh: it took two people to make a marriage, he reasoned, and some small share of the blame could always be apportioned to the other partner.

 Even assuming that the virus fulfilled its design goals precisely, Shawcross acknowledged a number of complications:

 Blood transfusions would become impractical until a foolproof method of killing the virus in vitro was found. Five years ago this would have been tragic, but Shawcross was encouraged by the latest work in synthetic and cultured blood components, and had no doubt that his epidemic would cause more funds and manpower to be diverted into the area. Transplants were less easily dealt with, but Shawcross thought them somewhat frivolous anyway, an expensive and rarely justifiable use of scarce resources.

 Doctors, nurses, dentists, paramedics, police, undertakers . . . well, in fact everyone, would have to take extreme precautions to avoid exposure to other people's blood. Shawcross was impressed, though of course not surprised, at God's foresight here: the rarer and less deadly AIDS virus had gone before, encouraging practices verging on the paranoid in dozens of professions, multiplying rubber glove sales by orders of magnitude. Now the overkill would all be justified, since everyone would be infected with, at the very least, SVC.