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Researchers from Australia and the United Kingdom report that the risk of developing MS was significantly reduced in a population of more than 20,000 people with HIV (human immunodeficiency virus, which causes the acquired immunodeficiency syndrome, or AIDS) infection identified through an English data set. It is not clear whether this association is related to the biological impact of HIV infection or its treatment with anti-viral therapies. Further study is necessary to understand the significance of these results. Julian Gold, MD (Prince of Wales Hospital, Sydney) and colleagues report their findings in the Journal of Neurology Neurosurgery and Psychiatry (published online August 4).

Background: The cause of MS is still unknown. Data from epidemiological studies (studies that analyze the geographical, socioeconomic, genetic and other factors that may contribute to who gets MS) suggest that exposure to an infectious agent may be involved in triggering the disease. To date, researchers have not been able to identify a single virus as the trigger for MS. Several viruses have been studied, but multiple steps are required in order to show that a particular virus causes MS. Researchers must prove that: the virus is in the body before MS develops, and the virus actually causes the disease and is not just happening alongside the disease.

In 2011, a case was reported in which a person with MS and HIV  was treated with anti-retrovirus therapy for the HIV infection, and did not experience MS disease activity for more than 10 years while on treatment (European Journal of Neurology 2011;18:e110-1) This led researchers in Denmark to study the incidence of MS in 5,018 people with HIV infection; they found a reduction of MS in this population but the results did not reach statistical significance. (Epidemiology 2013;24:331-2) The current study explores the question in a larger population.

The Study: Dr. Gold’s team obtained information on all people with HIV who were discharged from National Health Service hospitals in England between 1999 and 2011 from the English Hospital Episode Statistics data set. They analyzed the records of 21,207 HIV-positive patients and 5,298,496 controls, looking for differences in the proportion of people diagnosed with multiple sclerosis.
  
The results showed that HIV infection was associated with a significantly decreased risk of developing MS. It cannot be determined from this study whether this decrease was due to the HIV infection itself (since it has profound impacts on the immune system) or its treatment with anti-viral medications, since detailed information on HIV treatment was not captured in the database used in the study.

Conclusion: This study explores an intriguing observation and adds new evidence to a possible negative link between HIV and MS.  In an accompanying editorial, Mia L van der Kop (a doctoral student in epidemiology at the University of British Columbia Centre for Disease Control) comments, “Their replication of previous findings, the magnitude of their effect size and the statistical significance of their results combine to provide further evidence to support the hypothesis that there is an association between HIV (or its treatment) and a reduced risk of MS... A logical next step would be to directly examine the association between exposure to ART [antiretroviral treatment] and the development of MS.”

Read more about ongoing research to determine whether viruses play a role in MS.