Herpes viruses may play a role in the development of multiple sclerosis (MS). There are several types of herpes viruses, but researchers believe that only a few specific varieties increase a person’s risk of developing this neurological autoimmune disease.
Nearly all people will be infected with a herpes virus at some point in their lives, but not everyone will go on to develop MS. In this article, we’ll discuss what herpes viruses are and how they’re linked to MS development and flares.
Herpes viruses are a family of more than 100 viruses. Of all these, only eight are known to regularly infect humans. They include:
Normally, after most infections, your immune system clears away the virus so it can no longer infect you. Herpes viruses are able to become latent (dormant) and stay inside your body, without causing an active infection. Some viruses are even able to add their genes to your cells’ DNA — this “saves” the instructions to make more copies of the virus later.
MS develops when the immune system attacks the fatty coating, known as myelin, on the outside of nerve cells. When myelin is damaged, nerve cells have a hard time sending electrical signals through the central nervous system (CNS). As a result, communication between the brain and muscles gets disrupted, leading to several neurological symptoms.
MS is a demyelinating disease, meaning the nerve cells can’t make enough myelin for protection. Doctors and researchers have yet to determine the exact cause of MS, but they have a few theories. One is that infection with a certain type of herpes virus may overactivate the immune system, causing it to attack the CNS.
Several studies have investigated the link between EBV and MS. One large study of over 10 million military personnel found that EBV infection makes you 32 times more likely to develop MS. The more severe the EBV infection, the more likely MS might develop. The researchers also found that it takes around 10 years to develop MS symptoms after an EBV infection.
It’s known that EBV can become latent in immune cells called B cells, which are responsible for making antibodies. Researchers believe that these cells can collect in the brain of a person with MS. The infected B cells can also attract other types of immune cells that then create inflammation and damage the CNS. This malfunction of the immune system occurs only in people with certain genetic risk factors, especially for genes related to human leukocyte antigens (a type of molecule on the surface of cells).
Nearly all adults will become infected with EBV, but just a small portion of people go on to develop MS. Research suggests that infection is only one piece of the trigger for MS and that genetics and environmental factors can influence a person’s risk as well.
HHV-6 is another common herpes virus that infects most people during childhood. There are two types of HHV-6 — HHV-6A and HHV-6B. HHV-6A infection shows up more often in people with weakened immune systems, whereas HHV-6B is an extremely common infection seen in more than 90 percent of people worldwide.
Researchers have begun to study how HHV-6 may play a role in the development of MS. Studies show that HHV-6A can be found in MS lesions. DNA from the virus can also be seen in samples of cerebrospinal fluid (CSF) — fluid that surrounds the brain and spinal cord — from people with MS.
HV-6A can become latent in oligodendrocytes, which are cells in the CNS responsible for making myelin. Research suggests that HHV-6A may become reactivated in these cells, leading to inflammation and MS.
There is also evidence that myelin and HHV-6 have similar patterns that make them look alike. The immune system may get confused and overreact to myelin, mistaking it for the virus. The myelin is then destroyed, leading to the development of MS.
Studies have also investigated how herpes virus infections can affect MS relapses and symptoms. Researchers have found that active HHV-6 infection occurs more often in people during an MS relapse compared with when they’re in remission. This may indicate that infection with herpes virus triggers MS relapses and worsening of symptoms, but more research is needed to confirm this link.
Your immune system produces antibodies — immune proteins that target specific invaders — to help fight off viral infections. Doctors and researchers have noted that immunoglobulin G (IgG) antibody titers (levels) targeted to HHV-6 rise before an MS relapse. This means that antibody levels may be used to monitor disease activity and predict when someone may have a relapse.
The best way to avoid a viral infection is to limit contact with people who are sick. Many people with an EBV or HHV-6 infection have no symptoms, so the viruses can be unknowingly spread. If symptoms do show, they may include:
EBV spreads via bodily fluids such as saliva. You may become sick if you kiss or share a glass or silverware with someone who has EBV. HHV-6 is spread via respiratory fluids when an infected person coughs or sneezes. If someone around you shows symptoms of EBV or HHV-6, it’s best to limit contact until they’re feeling better.
If your doctor thinks you have an EBV infection, they can test for antibodies using a simple blood test. It takes time for your body to make antibodies against the virus, so you may need to be tested again after a few weeks to confirm a diagnosis. HHV-6 is detected with a polymerase chain reaction (PCR) test done on blood or saliva.
Researchers believe that staving off infection with herpes viruses may help prevent the development of MS. Unfortunately, there are no vaccinations to prevent infection with EBV or HHV-6. Clinical trials are studying an EBV vaccine, with the hopes of heading off infection and the development of autoimmune diseases like MS.
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