The MS Mystery

Canines may be the culprits carrying a slow virus

Researchers seeking the cause of multiple sclerosis, a disabling disease involving damage to the protective sheathing around nerve fibers, have long suspected that the answer might lie in a delayed reaction to a viral infection contracted years in the past. One suspect has been the measles virus, but 90% or more of all Americans in the prevaccination era got measles, while only a fraction of 1% developed MS. Now three New Jersey physicians have developed preliminary data suggesting that exposure to pet dogs may be related to MS.

Drs. Stuart D. Cook and Peter C. Dowling of the neurology service at the Veterans Administration Hospital in East Orange knew that while MS is not a directly inherited disease, it often strikes two and sometimes more members of a single family. They sought out 29 such patients and examined their patterns of pet ownership and exposure. It turned out that the MS families differed from their MS-free neighbors in one relevant respect: a greater proportion of them had small dogs (defined as those weighing less than 25 lbs., or 11.4 kg.) that stayed indoors much of the time. And the MS patients were found to have been exposed to their pets most intensively during the ten years before the first symptoms of their disease appeared. (In many cases, diagnosis is so difficult that MS cannot be confirmed for many years after these first symptoms.)

Especially striking was one family with four sisters, three of whom continued to live together in their childhood home and developed MS symptoms in 1974; the fourth sister, who had left home in 1971, remains free of any sign of the disease. The three homebodies had had close contact with the family dog, which suffered a severe brain disease in 1973. In ten other families, the mother and a child had the disease; in two, the father and a child; in 16, siblings were affected. Another coincidence involved a woman and her nephew, who lived together and both developed MS in the same year.

One of the many puzzling features of MS is its geographical distribution. It is most common in northern states and decreases in incidence toward the Gulf states and the tropics. Since dogs are about equally popular in both the North and South of the U.S., some questioners of the Cook-Dowling research have asked how dogs can have anything to do with the human disease. Bowling's answer: In the warmer South, dogs are less often kept indoors as house pets, but are left to roam more freely outside than in the cooler North.

Cook and Dowling made their first report in the London medical journal the Lancet. Now they have additional data prepared for publication, and another physician, Dr. Seymour Jotkowitz of Hackensack, has described an "impressive incidence of contact with sick dogs" in MS patients. Perhaps it is significant that among the many viruses that dogs harbor, one that causes distemper is a first cousin to that of the long-suspected human measles. Whether household pet dogs can ever be proved guilty of carrying an MS-related virus and what that virus may be are still open questions. Most veterinary authorities maintain that the evidence collected so far is not strong enough for pet owners to become alarmed. Even so, MS virology researchers intend to follow up the new scent.

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