ERV3-1 and myalgic encephalomeyelitis/chronic fatigue syndrome: In the same year De Meirleir and colleagues, using immunohistochemical methods, found immunoreactivity to HERV proteins (HERV-K, HERV-18, HERV-R and HERV-FRD) in dendritic cells of the duodenum of individuals diagnosed with the syndrome [10], suggesting that alterations in endogenous retroviruses expression pattern may occur in ME/CFS.