Since the 1980s, a child mummy buried in the Basilica of Saint Domenico Maggiore in Naples, Italy in the 16th century has been known as the earliest recorded case of smallpox in the world. The problem is, the 2-year-old didn’t have smallpox, according to new research spotted by IFLScience. But, as the scientists reexamining the remains discovered, it’s still a landmark study in disease evolution. It appears to be the earliest instance of hepatitis B that researchers have ever found in Italy, giving scientists insight into how the virus has evolved over the last several centuries.

The hepatitis B virus (HBV) attacks the liver and can result in cirrhosis and liver cancer, killing around 887,000 people per year. Though it can now be largely prevented by a vaccine, the World Health Organization estimates that 257 million people around the world live with HBV. It often affects children, spreading from mother to child during birth.

For the current study published in PLOS Pathogens, a team of researchers from McMaster University in Canada set about studying the child mummy with the hopes of continuing their past work nailing down how smallpox spread and evolved over human history. But when they used molecular analysis to study the mummy’s skin and bones, they didn’t find anything that indicated that the toddler had smallpox. Instead, they found the hepatitis B virus—which can cause a rash called Gianotti-Crosti Syndrome that the original researchers studying the mummy may have mistaken for the telltale rash associated with smallpox.

The ancient HBV strain found in the mummy's tissues had a genome closely related to that of the modern virus, which, The New York Times explains, could very well mean that the mummy was contaminated when it was first studied in the 1980s. But after analyzing the genetic material further and studying other examples of older HBV strains, they found that it’s plausible that the virus just hasn’t evolved extensively in the past 500 years. Though the contamination theory is still possible, it’s more likely that the mummy really does carry an ancient version of the virus. Considering that HBV has also been traced back to the 16th century in Asia, it’s likely that Europeans were suffering from it around the same time.

[h/t IFLScience]