Discussion: Animal Studies

Cutaneous lesions that develop in the rabbit following inoculation of tick homogenates infected with Lyme disease spirochetes closely mimic erythema chronicum migrans (ECM) in humans. Dr. Kornblatt was able to induce ECM-like lesions in rabbits at the site of inoculation within a short period of time, but Dr. Burgdorfer observed the development of skin lesions in remote sites up to 12 weeks after inoculation. Dr. Burgdorfer has so far been unable to detect the presence of spirochetes in rabbit skin lesions. Dr. Benach has induced skin lesions in rabbits at the site of tick homogenate inoculation, but they were 5-6 cm, indurated, raised le-sions with intense leukocytic infiltrates. The question was asked of Dr. Kornblatt if the erythematous lesions could have been reactive responses to tick material, rather than spirochetes. Dr. Kornblatt pointed out that he was working with pools of infected ticks in which approximately 25 percent of the ticks carried the Lyme agent. ECM-like lesions developed in only a few rabbits and these lesions contained spirochetes. Most rabbits did not develop lesions, suggesting that the erythema was in response to spirochetes, not tick foreign material. Spirochetes were present in both central and peripheral portions of skin lesions and were not associated with lymphatics or blood vessels. Biopsies were not taken after visible ECM-like lesions disappeared. The value of the rabbit as a model for Lyme disease in humans may be limited, since only ECM has been reproduced and not the other manifestations of Lyme disease. Other agents, such as Babesia microti, have been adapted to the mouse, allowing use of inbred strains and sophisticated immunological studies. Adaption of the Lyme agent to laboratory mice should be tried. It was pointed out that various species of animals may not develop the same disease pattern as the human and there is an advantage to using larger species, such as rabbit, dog, or monkey. A natural host may deal with the organism better than an atypical host, such as humans or laboratory rabbits. Since man is basically an intruder into the Lyme spirochete ecosystem, man is more likely to be susceptible to disease. That is why other animals are being examined. Furthermore, larger species of laboratory animals are more amenable to clinical studies and techniques such as arthroscopy and electrocar-diography. On the other hand, it may be advisable to see if natural hosts, such as white-footed mice, are susceptible to the …