More background on that Boston Globe article, which at least suggested b. miyamotoi is new. This is not exactly true.
The species was discovered in Japan in 1994-5, though not necessarily connected with human disease.
Relapsing fever as a clinical entity has a very long history going back to ancient Greece. Connection with spirochete species and transmission via tick vectors has been known to modern medicine for many years. The specific trail to discovery of the role of b. miyamotoi as a human pathogen was
described in Annals of Internal Medicine last year. It didn't just show up in Japan and
Russia, but also in locations like
Estonia and
Spain,
Michigan,
Washington ,
Tennessee and
California. Nobody should have been surprised to find
tick-borne relapsing fever in North America.
When b. miyamotoi was discovered in Japan the insect vector was ixodes persulcatus, which is widely distributed across Eurasia. It was reasonable to at least suspect that ixodes pacificus, ixodes ricinus and ixodes scapularis might also carry the spirochete. These did in fact turn up as vectors. The originally-discovered natural reservoir for the disease appeared to be a species of mouse native to Hokkaido, apodemus argentus. Any idea it was restricted to such rare mammalian hosts was quickly dispelled. It turned up in many mouse species, including mus musculus, which associates with humans. More troubling, it also turned up in rabbits, wild turkeys and passerine birds. When pathogens turn up in species humans hunt, eat or keep as pets, you need to consider this as a possible source of a zoonosis. Infections carried by passerine birds like songbirds are difficult to restrict to geographic localities.
The main reason this generally did not produce noted epidemics is that it was already widespread early in human history. There usually weren't enough surviving susceptible people to support a substantial epidemic. The main reason this infection was noticed in individual humans was the peculiar clinical sign of recurrent fever. Fever is only one manifestation of infection by spirochetes. Others fill thick books.
This makes the question of how doctors have been distinguishing infected patients from those with psychological problems in between episodes of fever, or in cases where immune response is impaired, even more problematic.
