Multiple sclerosis (MS) is an inflammatory neurological disorder that results when the myelin sheath covering nerves in the brain and spinal cord are damaged and stripped off. This results in neurological deficits such as intermittent blindness, numbness or tingling, and weakness. The disease is chronically progressive and sometimes follows a relapsing and remitting course where patient improve clinically only to worsen later in time. The disease can be severely debilitating and can result in paralysis of the affected individual. For many years, it was hypothesized to possibly result from a viral infection that triggered the illness in appropriately susceptible individuals. Evidence for the viral etiology of human multiple sclerosis has been lacking to date and all infectious hypotheses have remained unsubstantiated. Currently, no definitive cause for the disease has been identified. New research recently conducted at the Oregon Health and Science University, which was lead by Dr. Scott Wong, suggests that a multiple sclerosis like disease in Japanese macaques may be caused by a virus. The results of the research were recently published online in the journal Annals of Neurology. The authors have described a neurological condition called encephalomyelitis in the Japanese macaque colony at the Oregon National Primate Research Center which is similar to human multiple sclerosis. Since 1986, 57 Japanese macaques developed a disease that was marked by paralysis of one or more of their limbs. When the monkeys developed these symptoms, they were removed from the colony and humanely euthanized. The researchers analyzed the brain and spinal cord of eight monkeys with magnetic resonance imaging, and found the presence of white matter demyelinating lesions that were very similar to those seen in human multiple sclerosis. In addition to this finding, the researchers were able to culture a previously unknown virus belonging to the herpes virus family from the nervous tissue of the monkeys. The researchers wrote, “[Japanese macaque encephalomyelitis] is a unique spontaneous disease in a nonhuman primate that has similarities with multiple sclerosis (MS) and is associated with a novel simian herpesvirus. Elucidating the pathogenesis of [Japanese macaque encephalomyelitis] may shed new light on MS and other human demyelinating diseases”. This is a remarkable finding and suggests that the newly discovered herpes virus may be the causative agent in the development of this multiple sclerosis like disease in monkeys. Before this can be definitively concluded, the researchers will have to show that exposure to the virus reliably produces the illness. If the virus is the etiology in this monkey disease, there may be a human equivalent virus that is the cause of human multiple sclerosis. Multiple sclerosis researchers will now have a good monkey model of the disease to study which will hopefully shed light onto the cause in humans and possibly lead to better treatments, such as a vaccine.
Michael K. Axthelm et al. “Japanese macaque encephalomyelitis: A spontaneous multiple sclerosis–like disease in a nonhuman primate” Annals of Neurology 2011 69: n/a. doi: 10.1002/ana.22449