Cytomegalovirus-related sequence in an atypical cytopathic virus repeatedly isolated from a patient with chronic fatigue syndrome.

An atypical virus, cytopathic for human and animal fibroblasts, was repeatedly cultured from a patient with chronic fatigue syndrome. Viral particles, suggestive of cytomegalovirus (CMV) were seen by electron microscopy. Infected cells did not, however, stain with antisera specific for CMV, herpes, simplex virus, or human herpes-virus-6. Polymerase chain reaction (PCR) assays for these viruses were also negative. Two distinct products of approximately 1.5 kilobase pairs were amplified from virally infected cells using the human T lymphotropic virus-II tax gene reactive primer, SK44, in low stringency PCR. Sequencing of one of the amplified products showed a region of highly significant partial homology with the UL34 gene of CMV. The sequence of the other PCR product did not correspond with CMV or any other virus. DNA was extracted from the material pelleted by ultracentrifugation of filtered culture supernatants. It migrated in agarose gels as a single band of approximately 20 kpb. The banded DNA was digested with EcoRI and cloned. A 2.2 kbp plasmid containing the CMV-related sequence identified within the PCR product was recovered. Sequencing of this plasmid extended the region of partial sequence homology with CMV to include a portion of the UL35 gene of CMV. Initial sequencing of additional plasmids has confirmed the partial relatedness to CMV. The data indicate a novel type of CMV-related "stealth" virus that is able to establish a clinically persistent human infection.