Different methods are being tried in the attempt to make rabbit virulent Treponema pallidum harmless but still immunizing. James N. Miller in Los Angeles, working partly in collaboration with a group in the Netherlands, uses irradiation with gamma rays, which destroys the virulence of the spirochetes without stopping their movement. Rabbits inoculated with such irradiated treponemes developed both reagin type and immobilizing antibodies without showing symptoms. When virulent spirochetes were later injected into their skin these animals appeared in preliminary tests to be immune, and sensitive tests for virulent spirochetes in their tissues failed to reveal any. These are the most promising studies so far, but application to man is a long way off: In other experiments of this sort, not as well along as those of Miller, efforts are being made to alter spirochetes from rabbit testicles by chemical means; and in still others, the idea is to alter the virulent spirochete genetically so that it may retain its virulence and yet be cultivable. The interesting method being used in this last instance involves what amounts to a shotgun wedding of virulent spirochetes and Reiter culture treponemes, inoculated together into the testicles of rabbits. Up to 1968 the date of the most recent report these attempts had not yet succeeded.

Success in developing a vaccine for syphilis is obviously not in sight, and whether it is just around the corner is not to be guessed by anyone who hasn't been there. But even if it should succeed in its first phase even if a safe and effective immunizing agent could be developed serious obstacles both technical and nontechnical still lie in the road.

The technical obstacle inherent in all work on a syphilis vaccine is that antibodies to antigens in the vaccine will foul up the blood tests on which diagnosis of syphilis depends both reagin or Wassermann antibodies and those to the spirochetes themselves. Vaccines based on virulent spirochetes, or spirochete that had been virulent before their treatment for vaccine purposes, whether they came from chimpanzees, monkeys, baboons or rabbits, are likely to elicit both types of antibodies and, accordingly, if used at all widely, would make all the recipients Wassermann positive and TPI positive and so make diagnosis by blood tests impossible. We seem to face the extraordinary dilemma that, if we succeed in solving the major technical problem of syphilis control preparation of an effective vaccine we may receive in exchange the major technical problem of gonorrhea control lack of a satisfactory blood test!

But suppose the seemingly impossible proves no more that difficult, and only takes a little longer to get itself solved. Imagine materials and methods developed, with all the technical problems taken care of. Safe, effective vaccines, with no unpleasant or undesirable technical side effects.