Researchers have found a link between hepatitis B and C infection and Parkinson's disease.
Hepatitis B and C are two of the most common hepatitis viruses.
According to the World Health Organization (WHO), hepatitis B affects around 240 million people worldwide, and it is spread through contact with the blood, semen, and bodily fluids of infected individuals.
Around 130 to 150 million people across the globe have chronic hepatitis C - a bloodborne virus that is most commonly transmitted through sharing of injection equipment and the reuse or poor sterilization of needles and other medical equipment.
Most adults infected with hepatitis B will experience symptoms such as fever, fatigue, loss of appetite, abdominal pain, and dark urine. However, around 70 to 80 percent of adults with hepatitis C have no symptoms, meaning that most people do not realize that they are infected.
Previous studies have suggested a link between hepatitis virus infection and Parkinson's. One study published in 2015 suggested that there may be a link between hepatitis C infection and Parkinson's disease, but no such association was found with hepatitis B infection.
Findings may 'help us to better understand how Parkinson's develops'
For the new study - recently published in the journal Neurology - study author Julia Pakpoor, of the University of Oxford in the United Kingdom, and colleagues further investigated the relationship between hepatitis B and C and risk of Parkinson's.
Pakpoor and team used a large U.K. hospital database to reach their findings. This included almost 22,000 people with hepatitis B and 48,000 people with hepatitis C. Around 6,000 people with autoimmune hepatitis, 4,000 people with chronic active hepatitis, and nearly 20,000 people with HIV were also included.
The incidence of Parkinson's disease among these individuals was compared with a control group of more than 6 million people who visited the hospital for minor conditions, such as cataracts and bunions.
The researchers found that the risk of developing Parkinson's was 76 percent greater for people infected with hepatitis B, while individuals with hepatitis C were at a 51 percent increased risk of Parkinson's.
The team found no link between autoimmune hepatitis, chronic active hepatitis, or HIV and risk of Parkinson's.
Further research is needed to better understand the link between hepatitis B and C and Parkinson's, but Pakpoor and colleagues believe that their findings may help to shed light on the underlying causes of Parkinson's.
"The development of Parkinson's disease is complex, with both genetic and environmental factors. It's possible that the hepatitis virus itself or perhaps the treatment for the infection could play a role in triggering Parkinson's disease or it's possible that people who are susceptible to hepatitis infections are also more susceptible to Parkinson's disease.
We hope that identifying this relationship may help us to better understand how Parkinson's disease develops."
The researchers note that their study is subject to a number of limitations. For example, they were unable to account for lifestyle factors that might contribute to Parkinson's risk. Furthermore, the study only included hospital patients.