Could a sheep disease offer clues about MS?
Although its exact prevalence in the United States is not known, the condition tends to be more common the farther from the equator that one travels.
MS affects the central nervous system (CNS) and can cause a range of symptoms — often involving problems with movement, sensation, balance, and vision.
Symptoms generally appear when an individual is in their 20s or 30s. Some can be managed, and, in some cases, progression of the disease can be slowed. However, there is still no cure.
Hunting for a cause
MS is an autoimmune disease, in which the immune system attacks otherwise healthy tissue — in this case, the CNS. Why the immune system should turn on itself is still not understood.
Despite decades of work, the exact cause of the disease is still shrouded in mystery, though both genetic and environmental factors are thought to be involved.
Recently, a group of researchers at the University of Exeter in the United Kingdom looked for clues about MS's origins in a surprising place: sheep.
The first clues that sheep might provide some insight into MS came in 2013, when a team in the U.S. noticed that some people with MS had increased levels of antibodies to a toxin known as epsilon toxin (ETX).
In other words, ETX had entered their bodies and triggered an immune response, there producing antibodies that were kept in reserve, ready to attack the toxin if it returned in the future.
This toxin is produced by the bacterium Clostridium perfringens, found in the guts of livestock — most commonly in sheep.
ETX crosses the gut wall and builds up in the kidneys and brain. And, once in the brain, it destroys both the myelin that coats nerves and the cells that produce myelin. In sheep, this type of ETX poisoning is called enterotoxemia, or pulpy kidney disease.
Myelin is a waxy layer that coats many nerve cells. It is essential for carrying signals quickly and efficiently. In MS, myelin and the cells that produce it are destroyed by the immune system.
This striking similarity between enterotoxemia and MS makes any potential relationship worth investigating further.
Searching for ETX antibodies
The most recent study was led by Prof. Richard Titball, and the findings are published this week in the Multiple Sclerosis Journal.
Following up on earlier research, Prof. Titball and his team examined the blood of MS patients and a control group without MS. They measured levels of ETX antibodies using two different sampling methods to ensure accuracy.
They found that 43 percent of MS patients had ETX antibodies, compared with just 16 percent of the control group.
"There is a growing body of wider evidence that points to a hypothesis linking MS and ETX, and we are confident that these significant findings from our latest study will help people get even closer to an answer for the elusive triggers of MS."
Simon Slater, director, MS Sciences Ltd.
Of course, these are early findings, and more work will be needed to unpick the exact details of this relationship. Also, it is worth noting that some of the control group were carrying these antibodies, too, and they did not develop MS. So, other factors are certainly involved.
However, Slater is hopeful that this is the beginning of the path that leads to an effective treatment.
He goes on to say, "If the link between epsilon toxin and MS is proven, then this would suggest that vaccination would be an effective treatment for its prevention or in the early stages of the disease."
"Interestingly," concludes Slater, "although epsilon toxin is known to be highly potent, no human vaccine has ever been developed."