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 spirochetal infection in Ixodes ricinus ticks collected on Madeira Island and identified local reservoir hosts of both pathogen and vector tick. Spirochetes infect at least 1.3 % of the nymphal ticks collected in a particular 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 and domestic ungulates, on the other hand, were incompetent for Madeiran spirochetal isolates. Madeiran spirochetes stimulated rodents to recognize the same antigens as did spirochetes isolated on the European continent. The polymerase chain reaction amplified identical specific sequences of Madeiran spirochetes as of European-derived spirochetes. Rats 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 subtropical island some 10 degrees of latitude south of the northern Mediterranean coast. Because I. ricinus ticks frequently attack people on Madeira Island, Lyme disease should be considered as a cause of locally acquired human illness.