Hideyo Noguchi researched bacteria, including Treponema pallidum, the bacterium that causes syphilis, in Japan and the US during the early 1900s. Syphilis is a bacterial infection that spreads primarily through sexual transmission and can cause symptoms such as rashes, genital sores, and even organ damage. Noguchi recognized that Treponema pallidum causes neurosyphilis, which is when the syphilis infection spreads to the covering of the brain, the brain itself, or the spinal cord. Before Noguchi’s work, researchers knew about Treponema pallidum and the symptoms of the disease but did not know that untreated syphilis could lead to neurosyphilis. Additionally, Noguchi worked to alter and improve methods to diagnose syphilis. Noguchi’s work helped future researchers and doctors better diagnose people with syphilis, assisted them in understanding how to treat the disease’s long-term side effects, and helped them reduce the spread of syphilis, including between pregnant people and their fetuses.

In 1944, Joseph Earl Moore and colleagues published “The Treatment of Early Syphilis with Penicillin: A Preliminary Report of 1418 Cases,” hereafter “Treatment of Early Syphilis,” in the Journal of the American Medical Association. Moore and colleagues’ article was one of the first to study and explore the use of penicillin, an antibiotic that can kill bacteria, as a treatment for humans with syphilis, which is a bacterial disease that spreads through sexual contact. In its early stages, syphilis can cause rashes and genital sores, but in its late stages, it can also lead to organ damage. In “Treatment of Early Syphilis,” Moore and his colleagues explain that they conducted a study to determine the effects and optimal dose of penicillin in humans with early syphilis. The authors found that giving individuals with syphilis specific doses of penicillin can heal their syphilitic lesions and eradicate the bacterium that causes syphilis from their bodies. “Treatment of Early Syphilis” was one of the first articles to demonstrate that syphilis, specifically early syphilis, could be effectively treated with penicillin, the drug that physicians still most commonly use as of 2024 to treat the sexually transmitted disease.

Philippe Ricord was a nineteenth-century physician and surgeon in France who studied syphilis and demonstrated that it is different from gonorrhea. As of 2024, researchers recognize that syphilis and gonorrhea are both sexually transmitted infections, or STIs. However, the bacterium Treponema pallidum causes syphilis, leading to symptoms such as sores and fever, whereas the bacterium Neisseria gonorrhoeae causes gonorrhea and leads to different symptoms such as discharge from the urethra. Before Ricord, researchers thought syphilis and gonorrhea were the same disease. Ricord, through observation and experimentation, distinguished syphilis from gonorrhea and arranged the stages of syphilis into primary, secondary, and tertiary, each associated with different symptoms and levels of severity. By distinguishing syphilis from other STDs and accurately categorizing its stages, Ricord helped researchers better understand how to treat syphilis, a disease that can be transmitted from mother to child, causing life-threatening illness in infants.