A number of experts contacted by United Press International questioned the validity of the data used to support the theory, however.
"This is a new way of looking at multiple sclerosis -- it provides a testable hypothesis," Christopher Hawkes, a neurologist at London's Institute for Neurology and the expounder of the idea, told UPI.
"It's a sensitive subject, because if you had MS and you had a perfectly respectable upbringing, respectable life, with just one or two partners before you married, you wouldn't like to think it had the same stigma as something like syphilis," Hawkes said.
Sufferers of multiple sclerosis progressively develop scarring of the myelin, the protective sheath that covers the nerves. The condition leads to muscle weakness, blurred vision, slurred speech, tremors and other symptoms. MS affects as many as 500,000 people in the United States. There is no known cure.
Hawkes' research turned up four small MS epidemics that occurred on the Faroe, Orkney and Shetland islands and in Iceland following large influxes of Allied troops during World War II. This suggests sexual activity between women on the islands -- who previously had lower rates of infection -- and troops from geographic regions with higher rates of infection led to the outbreaks. There are questions about the accuracy of some of the relevant statistics, however.
Hawkes suggested -- as have other researchers -- that because the human T-Cell lymphotrophic virus-1, or HTLV-1, has been shown to cause a disease with symptoms quite similar to MS, a viral agent might be at work and might be transmitted sexually.
Among the studies cited by Hawkes are one done in Kashmir, India and another in Thugbah, Saudi Arabia, where extramarital sexual relations are thought to be relatively rare. Both showed extremely low rates of MS.
In contrast, research shows increased MS rates in western countries following the introduction of birth control pills and less use of barrier methods, beginning in the 1970s, he said.
"There is absolutely no data to support (this) hypothesis," Lauren Krupp, a neurologist and co-director of the MS center at the State University of New York at Stony Brook, told UPI. "For every point that the author raises to support his argument there is a very strong counter-argument," she said. "The specific kinds of things you would look for to support his argument aren't found in the existing data in the literature."
Krupp, who also is a spokeswoman for the National Multiple Sclerosis Society, cited a study -- also used by Hawkes -- of 13,000 married couples with one spouse contracting MS but showing no evidence of a higher rate of transmission to the other spouse.
Hawkes responded he thinks susceptibility to the disease is higher at younger ages and some studies of couples do show five times the rate expected in the general population. In addition, he said, in tropical spastic paraplegia, the disease caused by HTLV-1 -- which is known to be sexually transmitted -- transmission among married couples is relatively low. The same may be true for MS.
He acknowledged, however, that a virus, if it exists, also might need to act along with genetic susceptibility -- generally thought to be a key ingredient to developing the disease. "I say let's have a look at it rather than talking it into the ground. ... You've got to keep an open mind because nobody has the answer on MS," Hawkes said.
Although there may very well be a viral agent, or multiple viral agents, Krupp said, increased rates following higher levels of troops in isolated communities could be explained by viral transmission that was not necessarily sexual -- something Hawkes agrees is possible.
Graeme Stewart, an immunologist at Westmead Hospital in Sydney, Australia, told UPI, "The sexually transmitted infection hypothesis in multiple sclerosis is of low credibility."
Hawkes theory will be published in the October issue of the Journal of Neurology, Neurosurgery and Psychiatry.
Reported by Joe Grossman, UPI Science News, in Santa Cruz, Calif.)