Steere then learned about the work of the Swedish dermatologist Arvid Afzelius, who in 1909 had described an expanding, ring-like lesion and speculated that it was caused by the bite of an "Ixodes" tick. The rash described by Afzelius was later named erythema migrans. Research in Europe had found that erythema migrans and acrodermatitis chronica atrophicans, another rash caused by ticks in Europe, responded to penicillin, suggesting that the cause was bacterial, not viral. Yet no microorganisms could be found in fluid from the joints of Lyme disease patients.