Herpes Strain Found in Nervous System: Surprising Discovery

Researchers at the Seattle Children’s Research Institute have made an interesting discovery regarding the two most common strains of herpes, human herpes 6 (HHV-6) and human herpes 7 (HHV-7). According to the press release, 90% of the human population are estimated to have these herpes strains. Although more often than not these roseoloviruses do not tend to elicit severe symptoms when acquired by the human host, reactivation of dormant herpes viruses can have deadly implications.

Serge Barcy, PhD, research assistant professor at the Center for Global Infectious Disease Research, made a surprising discovery during his research of herpes viruses conducted at Seattle Children’s Research Institute: the HHV-7 virus was hidden in the nervous system of naturally infected pig-tailed macaques, a species of monkey. They named the HHV-6 and HHV-7 strains in the pig-tailed macaques MneH6 and MneH7 respectively, finding that the monkey’s strains were very similar both biologically and genetically to their human counterparts, according to the study.

Speaking of this interesting study and how it prompts further research, Dr. Barcy said, “It’s common to find herpes virus in salivary glands of humans and animals. But we found herpes 7 in the nervous system of animal models, which was a surprise because that strain of herpes has not been detected in the nervous system before. We want to understand what it does in the nervous system, if the virus is also in the human nervous system and if it could be associated with nerve diseases.”

When a herpes virus invades an individual, the body automatically responds in an effort to fight the infection. However, even after the individual gets better, some of the virus remains hidden within the body, lying dormant and undetected, such as in the case of chicken pox, a virus from the herpes family. “In a healthy child who gets chicken pox ... the body fights the virus and the child gets better. But dormant chicken pox virus remains in the body, and later in life something can trigger it and the person can develop shingles.” said Dr. Barcy.

According to the press release, researchers already know that when an individual is in need of a bone marrow transplant, one very dangerous side effect that may occur is inflammation of the brain, or encephalitis. When testing the individuals who ended up with encephalitis post-bone marrow transplant, doctors will often find that the encephalitis is the result of a herpes strain that is similar to HHV-7, called herpes 6b, reactivating in the patient’s body.

Speaking about the implications of herpes reactivating in bone marrow transplants, Dr. Barcy said, “It’s a classic case where a person has been infected with a common, benign herpes strain and never had trouble with it before. But then the person needs a bone marrow transplant for another medical condition, like leukemia. All of a sudden there is a risk that the herpes will reactivate after the bone marrow transplant and cause encephalitis.”

According to Dr. Barcy, more research will be needed in order to figure out if HHV-7 can cause damage when reactivated and how. Based on what is already known when it comes to herpes, if a person’s immune system is compromised or not particularly strong, the viruses can reactivate, and thus, cause severe systems that could potentially be deadly.

Dr. Barcy aims to conduct further research on finding out why HHV-7 was found in the immune systems of the animal models, and what it was doing while hidden away. Because other viruses are known to cause nerve diseases when interfering with myelin, a substance that surrounds and protects nerve cells, Dr. Barcy wants to study if HHV-7 interferes somehow with myelin.

When speaking of this future research, Dr. Barcy said, “More and more evidence is building that herpes viruses may use the nervous system as a highway to spread and could be interfering with normal nerve function under certain circumstances. Our next step in the research is to investigate this possible link.”