Abstract
A Babesia strain was isolated, in splenectomized monkeys, from the blood of a woman with babesiosis, apparently contracted by bites of infected ticks. Three consecutive passages of the parasite were made in splenectomized monkeys, and it was transmitted from the monkeys to hamsters, but not to dogs. Intraerythrocytic parasites appeared as spherical, ameboid, or elongated bodies, 1.5 to 2.5 µ in size. The parasite was limited by a single membrane. and its ultrastructural features were similar to those described for Babesia rodhaini. Indirect fluorescent-antibody tests showed that this (Gray) strain was serologically related to, but not identical with, Babesia canis. A capillary tube-agglutination test, with an antigen prepared from blood of a dog infected with B. canis, detected antibody in serum of infected monkeys, of the patient, and of her dog, but not her horse and donkey. We conclude that, in man, latent babesiosis, associated with babesiosis in animals, may be more common than supposed in rural populations.