TRANSMISSION OF THE AGENT OF LYME-DISEASE ON A SUBTROPICAL ISLAND

To determine whether the agent of Lyme disease (Borrelia burgdorferi) perpetuates on a subtropical island, we recorded prevalence of spiroch etal infection in Ixodes ricinus ticks collected on Madeira Island and identified local reservoir hosts of both pathogen and vector tick. Sp irochetes infect at least 1.3 % of the nymphal ticks collected in a pa rticular site. Subadult ticks frequently parasitized Norway as well as black rats on the island, and Lyme disease spirochetes were found in these hosts. Each was competent as reservoir host. Canaries, lizards a nd domestic ungulates, on the other hand, were incompetent for Madeira n spirochetal isolates. Madeiran spirochetes stimulated rodents to rec ognize the same antigens as did spirochetes isolated on the European c ontinent. The polymerase chain reaction amplified identical specific s equences of Madeiran spirochetes as of European-derived spirochetes. R ats appear to be the main reservoir hosts of the agent of Lyme disease on Madeira Island, and cattle and sheep serve as definitive hosts of the vector tick. The agent of Lyme disease is enzootic on this subtrop ical island some 10 degrees of latitude south of the northern Mediterr anean coast. Because I. ricinus ticks frequently attack people on Made ira Island, Lyme disease should be considered as a cause of locally ac quired human illness.