Syphilis
Syphilis is a nasty piece of work. Its exact origins are unknown, but cases began popping up in the late 15th century. Since then, "The Pox" as it's referred to in Britain has tormented people. Today treatment is effective but in the 19th century that wasn't the case. The term syphilis dates back to the 16th century where an Italian poet references a shepherd named Syphilus that became cursed by Apollo. German physician first described the early-stage genital lesions as so cruel and disgusting that nothing else on Earth could compare. After the lesions, or chancre, heal stage two sets in. Stage two consists of a full-body rash, wart-like sores, and flu-like symptoms. This stage is also the most contagious. The third stage is considered the latent stage since there are no physical symptoms, but rather the disease attacks the inner body working such as the brain and heart. This stage could last years until finally, ulcerations appear on the face. Once syphilis enters the nervous system, seizures and dementia can occur. Mercury was a common but expensive cure that also didn't do much good for other body factors. Due to this, public health campaigns began in 19th century Britain that targeted female sex workers as the room of the epidemic. The 1940s saw the invention of penicillin which is used to treat syphilis. But back in the 19th century, that didn't exist and therefore it's plausible it could be hidden within the pages of Anne Brontë's work.
**I'm not adding a picture of syphilis for obvious reasons