Researchers in Japan measured salivary human herpesvirus HHV-6 and HHV-7 and found they can be used as biomarkers to tell the difference between physiological (recovers with rest) fatigue and pathological fatigue.

In healthy people, HHV-6 and HHV-7 increased with training and work then rapidly decreased with rest. In people with chronic fatigue syndrome (CFS Fukuda criteria), obstructive sleep apnea syndrome and major depressive disorder, HHV-6 and HHV-7 did not increase.

The paper, Human herpesvirus 6 and 7 are biomarkers for fatigue, which distinguish between physiological fatigue and pathological fatigue, was published in Biochemical and Biophysical Research Communications September 2016.

The researchers used members of Japan’s Self Defence Force plus 113 more controls, 42 patients with sleep apnea, 97 chronic fatigue syndrome (Fukuda criteria) patients and 33 patients with major depressive disorder. Saliva was collected from the participants.

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Disease severity was not correlated with HHV-6 and HHV-7 DNA amounts.

“Everyone experiences physiological fatigue and recovers with rest. Pathological fatigue, however, greatly reduces quality of life and requires therapeutic interventions. It is therefore necessary to distinguish between the two but there has been no biomarker for this.”

The researchers, Ryo Aoki et al, chose to focus on human herpesvirus, which are reactivated by fatigue.  From other studies, they’ve found HHV-6 is  useful for monitoring cognitive function and adverse reactions in cancer chemotherapy, HHV-7 for assessing fatigue in end-stage renal disease.

“Our findings suggest a fundamentally new approach to evaluating fatigue.”