Discussion: Vector and Causative Agent

What is the simplest formulation of Kelly's medium for primary isolation of the Lyme disease spirochete? It has been suggested that one may use brain heart infusion broth rather than tissue culture medium and that many researchers have had success deleting some ingredients. One must be cautious, however, with substitutions and deletions. Modifications that support growth of laboratory-adapted strains may not be suitable for recovering primary isolations. Workers are urged to be compulsive about all steps in the preparation: making sure the water is doubledistilled, that the filters are changed, and that the glassware is free from detergent. One must take care to rinse every piece of glassware with distilled water. It is suggested that best results are obtained when one buys reagents, such as bovine serum albumin, in large volumes of a single lot that can be pretested. Has any laboratory attempted to grow the Lyme spirochete in tick tissue culture and, if so, what were the results? No one reported attempting to grow this organism in any of the tick tissue cultures available today. Certainly this is an area that requires further investigation. In the transmission cycle of Lyme disease, where is the "weakest link" where the spirochetes might be controlled? One suggestion is that deer constitute this "weak link" and the recommendation for area-wide control is deer removal. One must be cautious in making this recommendation, however; while long-term goals of tick control may be realized, the short-term effects may be disastrous. History has recorded many outbreaks of ectoparasite-borne diseases, including endemic relapsing fever, another tick-transmitted Borrelia infection, resulting from reductions in populations of a preferred host either by natural means or through human intervention. How did deer get reestablished on Nantucket? There was a male deer swimming near Nantucket in 1928. This animal was brought on to the Island. Several deer were introduced on to Nantucket from Michigan a few years later. It was these deer that replenished the herd on the Island. How does one account for the fact that human cases of babesiosis have been observed primarily on islands or along the coast, yet when we look at the distribution of Lyme disease, we find areas where there are many cases of Lyme disease, but none of babesiosis? This is, of course, a major difference in the epidemiology of babesiosis and of Lyme disease. One has a rather limited distribution and the other is found wherever the tick occurs. Two hypotheses are presented: (1) There may be a component of vertical transmission in the life cycle of the Lyme disease spirochete that is not present with Babesia. There may be some degree of inherited infection in Ixodes dammini. Although there is evidence of transovarial transmission, the spirochetes do not produce a generalized infection in the progeny. The spirochetes are