Chronic fatigue syndrome (CFS) is a serious systemic illness of unknown cause. A recent study identified DNA from a xenotropic murine leukemia virus-related virus (XMRV) in peripheral blood mononuclear cells (PBMCs) from 68 of 101 patients (67%) by nested PCR, as compared with 8 of 218 (3.7%) healthy controls. However, four subsequent reports failed to detect any murine leukemia virus (MLV)-related virus gene sequences in blood of CFS patients. We examined 41 PBMC-derived DNA samples from 37 patients meeting accepted diagnostic criteria for CFS and found MLV-like virus gag gene sequences in 32 of 37 (86.5%) compared with only 3 of 44 (6.8%) healthy volunteer blood donors. No evidence of mouse DNA contamination was detected in the PCR assay system or the clinical samples. Seven of 8 gag -positive patients tested again positive in a sample obtained nearly 15 y later. In contrast to the reported findings of near-genetic identity of all XMRVs, we identified a genetically diverse group of MLV-related viruses. The gag and env sequences from CFS patients were more closely related to those of polytropic mouse endogenous retroviruses than to those of XMRVs and were even less closely related to those of ecotropic MLVs. Further studies are needed to determine whether the same strong association with MLV-related viruses is found in other groups of patients with CFS, whether these viruses play a causative role in the development of CFS, and whether they represent a threat to the blood supply.

Oncogenic potential of human mycoplasmas was studied using cultured mouse embryo cells, C3H/10T1/2 (C3H). Mycoplasma fermentans and Mycoplasma penetrans, mycoplasmas found in unusually high frequencies among patients with AIDS, were examined. Instead of acute transformation, a multistage process in promotion and progression of malignant cell transformation with long latency was noted; after 6 passages (1 wk per passage) of persistent infection with M. fermentans, C3H cells exhibited phenotypic changes with malignant characteristics that became progressively more prominent with further prolonged infection. Up to at least the 11th passage, all malignant changes were reversible if mycoplasmas were eradicated by antibiotic treatment. Mycoplasma fermentans and Mycoplasma penetrans are the most common mycoplasmas associated with AIDS (1-3). M penetrans infects male homosexuals and is seroepidemiologically associated with Kaposi sarcoma (4). Wall-free mycoplasmas are among the few prokaryotes that can grow symbiotically and have a close interaction with mammalian cells for long periods of time without causing acute cytopathic effects. Thus, infections in cell culture are commonly unrecognized, and many persistent parasitic infections in humans or in animals are clinically silent (5,6). But what is the potential effect on mammalian hosts parasitically infected by the prokaryotes with seemingly low virulence? Can mycoplasmas, the simplest organisms capable of self-replication, alter significantly and permanently the biological properties of mammalian cells during the long course of persistent infection?In the 1960s, two studies reported that infection of mycoplasmas (Mycoplasma orale and one unspeciated) caused chromosomal changes (7,8). But the studies did not reveal that the cells underwent transformation. A separate study reported that introduction of mycoplasmas into cultures of baby hamster kidney (BHK) cells produced immediate morphological transformation with a higher soft agar cloning efficiency (9). Unfortunately, the BHK cells had a high rate of spontaneous transformation. In the 1980s, one article reported that an arthropod spiroplasma could rapidly transform mouse and monkey cells (10). Most scientists thought mycoplasmas simply introduced confusing artifacts that mimic cell transformation (11).Since the question of whether mycoplasmas can induce malignant transformation of mammalian cells may have great significance in general biology, tumor biology, as well as direct clinical implications, we have examined mycoplasmal transforming effects in the murine embryonic C3H/10T½/2 (C3H) cell system, pne of the few standard test systems available for studying potential carcinogenic agents or factors in animals or humans (12)(13)(14)(15). Using this model system with low inherent spontaneous transformation (12), we did not find mycoplasmas induced acute mammalian cell transformation described in the earlier studies. Instead, we found mycoplasma-mediated oncogenesis had a long latency and required a chronic pe...

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In the guts of more than 25 species of arthropods we observed filaments containing refractile inclusions previously discovered and named ''Arthromitus'' in 1849 by Joseph Leidy [Leidy, J. (1849) Proc. Acad. Nat. Sci. Philadelphia 4, 225-233]. We cultivated these microbes from boiled intestines of 10 different species of surface-cleaned soil insects and isopod crustaceans. Literature review and these observations lead us to conclude that Arthromitus are spore-forming, variably motile, cultivable bacilli. As long rod-shaped bacteria, they lose their flagella, attach by fibers or fuzz to the intestinal epithelium, grow filamentously, and sporulate from their distal ends. When these organisms are incubated in culture, their life history stages are accelerated by light and inhibited by anoxia. Characterization of new Arthromitus isolates from digestive tracts of common sow bugs (Porcellio scaber), roaches (Gromphodorhina portentosa, Blaberus giganteus) and termites (Cryptotermes brevis, Kalotermes flavicollis) identifies these flagellated, spore-forming symbionts as a Bacillus sp. Complete sequencing of the 16S rRNA gene from four isolates (two sow bug, one hissing roach, one death's head roach) confirms these as the low-G؉C Gram-positive eubacterium Bacillus cereus. We suggest that B. cereus and its close relatives, easily isolated from soil and grown on nutrient agar, enjoy filamentous growth in moist nutrient-rich intestines of healthy arthropods and similar habitats.

Murine leukemia viruses (MLV), including xenotropic-MLV-related virus (XMRV), have been controversially linked to chronic fatigue syndrome (CFS). To explore this issue in greater depth, we compiled coded replicate samples of blood from 15 subjects previously reported to be XMRV/MLV-positive (14 with CFS) and from 15 healthy donors previously determined to be negative for the viruses. These samples were distributed in a blinded fashion to nine laboratories which performed assays designed to detect XMRV/MLV nucleic acid, virus replication, and antibody. Only two laboratories reported evidence of XMRV/MLVs; however, replicate sample results showed disagreement and reactivity was similar among CFS subjects and negative controls. These results indicate that current assays do not reproducibly detect XMRV/MLV in blood samples and that blood donor screening is not warranted.