Adults with a history of chicken pox or shingles infections had a fourfold increased risk for developing multiple sclerosis, researchers said.
In a population-wide epidemiological study conducted in Taiwan, the hazard ratio for MS diagnosis within a year of such infections, relative to those without such a history, was 3.96 (95% CI 2.22 to 7.07), reported Herng-Ching Lin, PhD, of Taipei Medical University.
Moreover, the mean time between the acute infection and MS diagnosis was just 104 days.
"Our findings suggest that the occurrence of MS could be associated with herpes zoster attack," Lin and colleagues wrote online in the Journal of Infectious Diseases.
It's the first large-scale study to support previous suggestions that MS may be triggered or exacerbated by herpes zoster (also known as varicella zoster) virus, the agent responsible for chicken pox and shingles.
The virus infects the central nervous system. Typically, after the initial chicken pox attack, the virus becomes latent in the dorsal root ganglion. Years later, what Lin and colleagues called "immunological derangement" or other triggers can reactivate the virus to cause skin eruptions with severe pain.
Herpes zoster has long been suspected of playing some type of causative role in MS -- for example, demyelination has occasionally been seen in conjunction with severe herpes zoster attacks -- but the rarity of MS in the population has made epidemiological studies difficult.
Lin and colleagues drew on records from the Taiwan National Health Insurance Research Database, which covered some 22.6 million people as of 2007 -- more than 98% of the entire Taiwanese population. It includes monthly claims summaries and care orders for participants, including ambulatory and inpatient care.
The researchers identified about 317,000 adults who had a principal diagnosis of herpes zoster infection from 2003 to 2005. Among them, 29 developed MS during the year after this diagnosis was recorded.
For comparison, Lin and colleagues also examined records of 946,650 other randomly selected adults who had ambulatory care visits during this same period, matched 3:1 for age, sex, and year of visit to the individuals with herpes zoster attacks.
In the control group, 24 individuals were diagnosed with MS during the year after the index ambulatory care visit.
The researchers found that those with herpes zoster had slightly but significantly higher monthly income and were more likely to live in the northern part of the country than the control group. These factors were taken into account in the statistical analysis that led to the hazard ratio of 3.96 for MS diagnosis following herpes zoster attacks.
The analysis did not include counting everyone with a diagnosis of MS and checking for a history of herpes zoster infection.
Nevertheless, in an accompanying editorial, two Mexican researchers agreed that the findings significantly bolster the case for a connection between the virus and MS.
"The evidence provided in this study ... allows us to better understand the role of these viral factors as an MS risk among certain genetically susceptible individuals," wrote Teresa Corona, MD, and José Flores, MD, of the National Institute of Neurology and Neurosurgery in Mexico City.
Lin and colleagues said the mechanisms by which the virus may cause or worsen MS remain unknown, although speculation centers on alterations in immune functioning that lead to autoimmunity against myelin.
Corona and Flores offered one specific possibility: "reactivation of latent herpes viruses by other infectious agents, and cross-recognition of common viral antigens with antigens found in the myelin sheath, which thereby induces molecular mimicry or superantigens," they wrote.
Lin and colleagues noted some limitations to their study, including its reliance on potentially flawed administrative data, lack of information on potential confounders such as smoking status, and the possibility that some people with herpes zoster attacks did not seek treatment.
Also, they stressed that it was restricted almost exclusively to people of Han Chinese ancestry living in Taiwan.
Corona and Flores recommended that similar studies be undertaken elsewhere in the world to confirm the association in other ethnic groups.
The database used in the study is managed by the Taiwan Department of Health.
Study authors declared they had no relevant financial interests.
