It’s estimated that about 70 percent of the world’s population carries live cytomegalovirus — one of the herpes family of viruses — in their bodies. In most cases, the person remains completely unaware of the infection because the virus is dormant or latent.

But if his or her immune system is weakened, those viruses can become activated and cause severe illness. You see this in people who have undergone transplants and are taking immune suppressants, or people with immune-suppressing cancers. They can die of overwhelming cytomegalovirus infections.

The same is true with other herpes viruses, such as the Epstein-Barr virus. Some bacteria and mycoplasma — such as Chlamydia pneumoniae, Borrelia burgdorferi (Lyme disease), and H. pylori — can also go dormant. And there are also some 50 species of mycobacteria (other than the tuberculosis organism) that may remain hidden in the body.

All of those organisms cause chronic, smoldering inflammation, and lead to conditions ranging from cancer to neurodegenerative disorders, including possibly Alzheimer’s dementia and Parkinson’s disease.

Diagnosing these infections can often be difficult, and in some cases very expensive. The least expensive methods are immune antibody tests such as the ELISA test or Western blot testing. Of those two, ELISA is much less accurate.

The most accurate test for specific infections is the polymerase chain reaction (PCR) test — though it has some limitations.

If you have persistently high inflammation, you should have your doctor pursue these tests. Lyme disease and mycoplasma infections are increasing at an alarming rate, and many cases go undiagnosed. These infections cause a number of symptoms in their active phases, and in some cases latent infection can trigger smoldering inflammation that may lead to:

• Alzheimer’s dementia

• Parkinson’s disease

• ALS

• Chronic fatigue syndrome

• Fibromyalgia

Viruses such as herpes can also infect blood vessels, leading to rapidly advancing atherosclerosis.