Infection with the human immunodeficiency virus (HIV) may reduce the risk of multiple sclerosis, according to new research.
A team of British and Australian researchers discovered that people with HIV have a significantly lowered risk of developing MS, a debilitating disease affecting nerves in the brain and spinal chord.
It is not yet clear if the lowered risk is caused by the HIV virus itself or by the antiretroviral drugs taken by sufferers. If antiretroviral drugs are the key, the treatment could be used to help MS patients.
Multiple Sclerosis causes symptoms including problems with muscle movement, balance and vision.
The study began after the discovery of an Australian man who was diagnosed with MS several months after being confirmed as having HIV.
His symptoms of MS disappeared entirely after he began starting antiretroviral drugs, used to treat HIV. Over a 12-year monitoring period, he remained completely free of symptoms.
In the most recent study, a team led by Julian Gold, a professor at the Prince of Wales Hospital in Sydney, examined British data which detailed hospital treatment in England between 1999 and 2011.
In this period, the data for more than 21,000 people with HIV was compared with data for a group of around 5.3 million people who did not have HIV.
In the HIV group, only seven people developed MS over the ensuing years, far fewer than the 18 that would have otherwise been expected - a risk reduction of nearly two-thirds.
The longer a person had HIV, the less likely they were to develop MS, US News and World Report stated. Compared with people in the general population, the risk of MS was 75% lower among people who had tested positive for HIV more than a year ago.
Researchers from Oxford University, Queen Mary University of London and the Prince of Wales Hospital in Sydney were all involved in the study.
The researchers said: "If subsequent studies demonstrate there is a causal protective effect of HIV [and/or its treatment], and if the magnitude of it proves to be similar to our rate ratio of 0.38, this would be the largest protective factor yet observed in relation to MS."
Dr Emma Gray, research communications manager at the MS Society, told the Independent: "This is a valuable and intriguing new study. Much more research is needed to definitively prove whether having HIV or being treated for HIV with antiretrovirals, or even a combination of the two, reduces the risk of someone developing MS."
The authors acknowledged weaknesses in the study, for example, it is unknown whether patients with HIV took antiretroviral drugs to suppress the virus.
According to the researchers, MS may be dampened because the immune system is brought back under control.
"Further investigation of our finding has the potential, after more than 170 years since MS was first described... to reveal the causes of MS," they added.
The research was published in the Journal of Neurology, Neurosurgery & Psychiatry.