The newly described human metapneumovirus (hMPV) is reported here to be more commonly associated with lower respiratory tract disease. The present study examined nasal swab specimens from 90 infants with acute respiratory tract infections in Pisa, Italy, over a period of three respiratory virus seasons. The incidence of infection varied in each of the 3 years, with the rates of positivity for hMPV being 7% in 2001 but 37 and 43% in 2000 and 2002, respectively. hMPV was noted to occur seasonally in a pattern typical of the frequency of occurrence of respiratory syncytial virus. More than one-half (14 of 23) of the infants infected with hMPV had bronchopneumonia. One-third (9 of 23) of the hMPV-infected patients were also infected with another respiratory virus, a relationship that has not previously been reported. Mixed infections did not account for a higher percentage of cases of bronchopneumonia than hMPV infection alone did. Furthermore, 7 of 17 infants whose plasma was also tested for hMPV RNA were demonstrated to have virus in both nasal swab and blood specimens. The study indicates that hMPV is seen as commonly as other respiratory viruses, may be associated with severe respiratory disease in infants, can establish mixed infections with other respiratory viruses, and has a seasonal occurrence.

Active infection with torquetenovirus (TTV) has been associated with an increased severity of diseases in which inflammation plays a particularly important pathogenetic role. Here, we report that cloned DNA of a genogroup 4 TTV (ViPiSAL) is an activator of proinflammatory cytokine production by murine spleen cells and that the effect is mediated via toll-like receptor (TLR)9. The same DNA also increased the levels of proinflammatory cytokines induced by two well-characterized TLR9 stimulants. Finally, in silico analyses of the genomes of ViPiSAL and other TTVs revealed marked differences in the representation of CpG motifs known to be most effective at activating immune cells via TLR9. These findings demonstrate for the first time that at least one TTV isolate has the potential to stimulate and co-stimulate inflammatory responses.

In 239 torquetenovirus-positive people, multiple-genogroup infections were common and associated with higher viral loads than would be expected from simple additive effects. The latter observation was restricted to the infections which included both genogroups 1 and 3, pointing to the possible existence of some kind of infection facilitation between these genogroups.Torquetenovirus (TTV), formerly known as TT virus, was discovered in 1997 by Japanese workers in the blood of a patient with cryptogenetic hepatitis and has since been shown to sustain long-term, possibly permanent viremia in a surprisingly high proportion (around 80%) of the general population worldwide (1-3, 5, 12, 13). It is also clearly documented that the loads of TTV (viral load [VL]) in plasma may differ extensively among individual hosts (15). Due to its high genetic heterogeneity, TTV is currently subdivided into five highly divergent genogroups, designated 1 to 5 (4, 14). Although multiple-genogroup TTV infections are quite frequent (1, 6, 7), there have been no reported studies on the possible relationships between the number of genogroups carried and the total VL present in an individual.In the course of our studies, we noted that individuals with high VLs tended to yield more TTV genogroups than those with low VLs. Thus, in preliminary work, we examined whether this might be due to the fact that high VLs permitted detection of TTV genogroups which escaped detection in low-VL plasma because they represented a small fraction of the total VL. The experiments did not support this explanation. In particular, the processing of five low-VL plasma specimens that had yielded one or two TTV genogroups in such a way as to augment 10-and 100-fold the amount of DNA examined in the typing assays had little or no impact on the number of genogroups detected. Similarly, when five specimens positive for four genogroups and with VLs between 6.1 and 6.8 log 10 copies per ml were diluted 100-fold, i.e., to a point where the VLs were in the range that is associated mostly with single-genogroup infections, they still yielded three to four TTV genogroups (data not shown).Such failure to provide an easy explanation for the observation prompted a systematic look at the issue. To this purpose, we assessed the presence, load, and genogroup(s) of TTV in plasma samples from 300 people. The methods have been previously reported (8, 9, 15). Briefly, extracted DNA was assayed for TTV presence and load with a universal TaqMan real-time PCR having the potential to detect and quantitate all hitherto-recognized genetic forms of the virus (8, 9). TTVpositive DNA extracts were then typed with five distinct genogroup-specific PCRs, as described previously (8, 9), using the primer sets shown in Table 1. TTV was detected in 267 people (89%) and successfully typed in 239. Most TTV-positives carried two distinct genogroups, followed by one, three, and four. TTV genogroups 1 and 3 were the most prevalent, followed at a distance by genogroups 4 and 5, while genogroup 2 was rather in...

Many aspects of the life cycle of torquetenoviruses (TTVs) are essentially unexplored. In particular, it is still a matter of speculation which cell type(s) replicates the viruses and maintains the generally high viral loads found in the blood of infected hosts. In this study, we sequentially measured the TTV loads in the plasma of four TTV-positive leukemia patients who were strongly myelosuppressed and then transplanted with haploidentical hematopoietic stem cells. The findings provide clear quantitative evidence for an extremely important role of hematopoietic cells in the maintenance of TTV viremia.Torquetenoviruses (TTVs) are small naked DNA viruses distinguished by a circular single-stranded DNA genome of only 3.8 kb, classified within the newly established family Anelloviridae (7). TTVs have been found in several animal species but do not appear capable of interspecies transmission. Due to their extensive genetic heterogeneity, human TTVs have been operatively subdivided into 5 genogroups and more than 40 genotypes (4). A remarkable feature of these TTVs is their presence in the plasma of nearly all people, regardless of geographical origin, age, and health status, raising many questions about their life cycle and possible pathological implications (2, 5). Plasma loads of TTVs vary extensively in both healthy and diseased individuals, usually ranging between 10 3 and 10 7 DNA copies per ml of plasma. However, some patients, including those with selected inflammatory or neoplastic disorders, transplant recipients, and human immunodeficiency virus-infected individuals, have a tendency to carry especially high burdens of TTVs (1,6,13,(22)(23)(24).By studying the dynamics of TTV viremia in individuals treated with alpha interferon for hepatitis C, the kinetics of virus replication was found to be quite high, with numbers of virions released into plasma and cleared from it daily on the same order of magnitude as other chronic plasma viremiainducing viruses, such as the hepatitis B, hepatitis C, and human immunodeficiency viruses (16). Yet, due to considerable difficulties encountered in propagating TTVs in culture and in distinguishing the virions passively adsorbed onto the cells from the ones replicating inside cells, the tissue or tissues where these large numbers of TTV virions originate have yet to be established. Given that the amino acid compositions of the capsid protein believed to mediate viral adsorption to cells are quite diverse in different TTVs (2, 3, 9), it is also possible that permissive cells vary depending on the TTV considered. Relevant studies are limited. Short-term cultures of phytohemagglutinin-stimulated peripheral lymphocytes, but not resting lymphocytes were found to permit a measurable level of TTV replication (15, 18), indicative of at least a moderate degree of lymphotropism. On the other hand, the detection of replicative forms of TTV DNA in several tissues, including bone marrow, peripheral blood mononuclear cells, and liver, has suggested that TTVs might be polytropic in natur...

TT virus (TTV) produces chronic plasma viremia in around 90% of healthy individuals of all ages and has, therefore, been proposed as a commensal human virus. We recently demonstrated that in children hospitalized for acute respiratory diseases high TTV loads were associated with severe forms of disease. Here, we report that in such children TTV loads showed an inverse correlation with the percentage of circulating total T and helper T cells and a direct correlation with the percentage of B cells. Thus, florid TTV replication might contribute to lymphocyte imbalances and, possibly, immunosuppressive effects, thus resembling related animal viruses.TT virus (TTV) has genome properties similar to those of animal circoviruses, such as chicken anemia virus and porcine circovirus. Because it produces chronic plasma viremia in around 90% of healthy individuals of all ages worldwide and no associated disease has yet been identified, it has been suggested that TTV might be totally apathogenic (for reviews, see references 1 and 11). Recently, we tested for the presence of TTV and assessed viral load by universal untranslated-region real-time PCR in 157 children under 2 years old with acute respiratory diseases (ARD) on the day of hospital admission and obtained convincing data that TTV might replicate in the respiratory tract (5). Also, although we found no evidence that TTV might be the direct cause of ARD, TTV loads in both nasal swabs and plasma samples were substantially higher in subjects with bronchopneumonia (BP) than in the subjects with milder ARD (laryngitis, bronchitis, and bronchiolitis), suggesting among other possibilities that TTV could be locally or systemically immunosuppressive and aggravate disease induced by other agents (5). However, there is no information on this matter except for recent reports showing an inverse relationship between TTV burdens and CD4 cell counts in patients with human immunodeficiency virus type 1 (2, 10, 13).In this study, we examined, with informed parental consent, peripheral leukocyte and lymphocyte subset counts in 40 randomly chosen children with ARD from the above study (5). Of the 40 children, 18 had an X-ray-confirmed diagnosis of BP. The same blood samples used for TTV assays were analyzed. Features similar to those described for the entire sample (5) were confirmed in this subset. In particular, mean TTV loads in plasma were significantly higher in BP patients than in children with milder ARD (7.9 Ϯ 1.2 versus 5.6 Ϯ 2.3 log 10 per ml [P Ͻ 0.001]). Interestingly, although all absolute cell counts were within the values reported for healthy children of similar age (3) with unknown TTV status (but presumably mostly TTV positive, based on what is currently known of TTV epidemiology [1,11]), the percentages of CD3 (total T lymphocytes) and CD4 cells (T helper lymphocytes) showed an inverse correlation with the levels of TTV. By contrast, the percentages of CD19 cells (B lymphocytes) showed a positive correlation with TTV levels (Fig. 1). On the other hand, lymphocyte and TT...