Human polyomavirus 9 infection in kidney transplant patients.

Several human polyomaviruses of unknown prevalence and pathogenicity have been identified, including human polyomavirus 9 (HPyV9). To determine rates of HPyV9 infection among immunosuppressed patients, we screened serum samples from 101 kidney transplant patients in the Netherlands for HPyV9 DNA and seroreactivity. A total of 21 patients had positive results for HPyV9 DNA; positivity rates peaked at 3 months after transplantation, but the highest viral loads were measured just after transplantation. During 18 months of follow-up, HPyV9 seroprevalence increased from 33% to 46% among transplant patients; seroprevalence remained stable at ≈30% in a control group of healthy blood donors in whom no HPyV9 DNA was detected. Further analysis revealed an association between detection of HPyV9 and detection of BK polyomavirus but not of cytomegalovirus. Our data indicate that HPyV9 infection is frequent in kidney transplant patients, but the nature of infection-endogenous or donor-derived-and pathogenic potential of this virus remain unknown.

Molecular profiling of cutaneous squamous cell carcinomas and actinic keratoses from organ transplant recipients.

BACKGROUND: The risk of developing cutaneous squamous cell carcinoma (SCC) is markedly increased in organ transplant recipients (OTRs) compared to the normal population. Next to sun exposure, the immunosuppressive regimen is an important risk factor for the development of SCC in OTRs. Various gene mutations (e.g. TP53) and genetic alterations (e.g. loss of CDKN2A, amplification of RAS) have been found in SCCs. The aim of this genome-wide study was to identify pathways and genomic alterations that are consistently involved in the formation of SCCs and their precursor lesions, actinic keratoses (AKs). METHODS: To perform the analysis in an isogenic background, RNA and DNA were isolated from SCC, AK and normal (unexposed) epidermis (NS) from each of 13 OTRs. Samples were subjected to genome-wide expression analysis and genome SNP analysis using Illumina's HumanWG-6 BeadChips and Infinium II HumanHap550 Genotyping BeadChips, respectively. mRNA expression results were verified by quantitative PCR. RESULTS: Hierarchical cluster analysis of mRNA expression profiles showed SCC, AK and NS samples to separate into three distinct groups. Several thousand genes were differentially expressed between epidermis, AK and SCC; most upregulated in SCCs were hyperproliferation related genes and stress markers, such as keratin 6 (KRT6), KRT16 and KRT17. Matching to oncogenic pathways revealed activation of downstream targets of RAS and cMYC in SCCs and of NFκB and TNF already in AKs. In contrast to what has been reported previously, genome-wide SNP analysis showed very few copy number variations in AKs and SCCs, and these variations had no apparent relationship with observed changes in mRNA expression profiles. CONCLUSION: Vast differences in gene expression profiles exist between SCC, AK and NS from immunosuppressed OTRs. Moreover, several pathways activated in SCCs were already activated in AKs, confirming the assumption that AKs are the precursor lesions of SCCs. Since the drastic changes in gene expression appeared unlinked to specific genomic gains or losses, the causal events driving SCC development require further investigation. Other molecular mechanisms, such as DNA methylation or miRNA alterations, may affect gene expression in SCCs of OTRs. Further study is required to identify the mechanisms of early activation of NFκB and TNF, and to establish whether these pathways offer a feasible target for preventive intervention among OTRs.

Beta-papillomavirus DNA loads in hair follicles of immunocompetent people and organ transplant recipients.

There is increasing evidence of an association between human papillomaviruses (HPV) of the beta-genus (beta-PV) and the development of cutaneous squamous cell carcinoma (SCC). The viral DNA load may be an important determinant of pathogenicity, but there are currently no baseline epidemiological data relating to load in people without SCC. We investigated DNA-loads of eight beta-PV types previously associated with risk of SCC. We collected eyebrow hairs from immunocompetent people (ICP) and organ transplant recipients (OTR), determined load by quantitative PCR and obtained demographic, phenotypic, and sun exposure information. Viral loads for ICP from Australia (n = 241) and Italy (n = 223) and OTR from across Europe (n = 318) spanned seven orders of magnitude. The median loads for all types were below one viral DNA copy per 60 cells and were highest for HPV5, HPV8 and HPV20. None of the populations had consistently higher viral loads for all 8 types. However, a higher proportion of OTR were in the top deciles of viral load distributions for six of the eight beta-PV types examined. In a nested analysis of Italian OTR and ICP, this finding was significant for six beta-PV types and cumulative load. Increasing age was significantly associated with higher viral loads in Australia, and there was a weak trend for higher loads with the time elapsed since transplantation in the OTR. We observed a wide distribution of beta-PV loads with OTR significantly more likely to have the highest viral loads. Thus, viral loads may be an important contributor to the higher risk of SCC in OTR.

Cryotherapy with liquid nitrogen versus topical salicylic acid application for cutaneous warts in primary care: randomized controlled trial.

BACKGROUND: Cryotherapy is widely used for the treatment of cutaneous warts in primary care. However, evidence favours salicylic acid application. We compared the effectiveness of these treatments as well as a wait-and-see approach. METHODS: Consecutive patients with new cutaneous warts were recruited in 30 primary care practices in the Netherlands between May 1, 2006, and Jan. 26, 2007. We randomly allocated eligible patients to one of three groups: cryotherapy with liquid nitrogen every two weeks, self-application of salicylic acid daily or a wait-and-see approach. The primary outcome was the proportion of participants whose warts were all cured at 13 weeks. Analysis was on an intention-to-treat basis. Secondary outcomes included treatment adherence, side effects and treatment satisfaction. Research nurses assessed outcomes during home visits at 4, 13 and 26 weeks. RESULTS: Of the 250 participants (age 4 to 79 years), 240 were included in the analysis at 13 weeks (loss to follow-up 4%). Cure rates were 39% (95% confidence interval [CI] 29%-51%) in the cryotherapy group, 24% (95% CI 16%-35%) in the salicylic acid group and 16% (95% CI 9.5%-25%) in the wait-and-see group. Differences in effectiveness were most pronounced among participants with common warts (n = 116): cure rates were 49% (95% CI 34%-64%) in the cryotherapy group, 15% (95% CI 7%-30%) in the salicylic acid group and 8% (95% CI 3%-21%) in the wait-and-see group. Cure rates among the participants with plantar warts (n = 124) did not differ significantly between treatment groups. INTERPRETATION: For common warts, cryotherapy was the most effective therapy in primary care. For plantar warts, we found no clinically relevant difference in effectiveness between cryotherapy, topical application of salicylic acid or a wait-and-see approach after 13 weeks. (ClinicalTrial.gov registration no. ISRCTN42730629).

Betapapillomaviruses: innocent bystanders or causes of skin cancer.

Human papillomaviruses (HPV) are found in almost all squamous epithelia where they can cause hyperproliferative disease of mucosa and skin. Mucosal HPV types, such as HPV6 and HPV16, are known to cause anogenital warts and dysplasia or neoplasia, respectively. These HPV types have been studied extensively, and for some of them recently preventive vaccines have become available. Although HPV that populate the skin were the first identified HPV types, knowledge of the pathogenicity of HPV in the cornified epithelia stayed behind. What the majority of cutaneous HPV types do, for instance those belonging to the beta genus (betaPV), is largely unknown. As the number of reports that describe epidemiological associations between markers of betaPV infection and skin cancer gradually increases, the need for basic knowledge about these viruses grows as well. This review aims to picture what is currently known about betaPV with respect to infection, transmission and transformation, in order to envisage their potential role in cutaneous carcinogenesis.

Tumor cell-specific AIM2 regulates growth and invasion of cutaneous squamous cell carcinoma.

Cutaneous squamous cell carcinoma (cSCC) is the most common metastatic skin cancer. Inflammation is a typical feature in cSCC progression. Analysis of the expression of inflammasome components in cSCC cell lines and normal human epidermal keratinocytes revealed upregulation of the expression of AIM2 mRNA and protein in cSCC cells. Elevated levels of AIM2 mRNA were noted in cSCCs in vivo compared with normal skin. Strong and moderate tumor cell specific expression of AIM2 was detected with immunohistochemistry (IHC) in sporadic human cSCCs in vivo, whereas expression of AIM2 was moderate in cSCC in situ (cSCCIS) and low or absent in actinic keratosis (AK) and normal skin. IHC of cSCCs, cSCCIS and AKs from organ transplant recipients also revealed strong and moderate tumor cell specific expression of AIM2 in cSCCs. Knockdown of AIM2 resulted in reduction in viability of cSCC cells and onset of apoptosis. RNA-seq and pathway analysis after knockdown of AIM2 in cSCC cells revealed downregulation of the biofunction category Cell cycle and upregulation of the biofunction category Cell Death and Survival. Knockdown of AIM2 also resulted in reduction in invasion of cSCC cells and downregulation in production of invasion proteinases MMP1 and MMP13. Knockdown of AIM2 resulted in suppression of growth and vascularization of cSCC xenografts in vivo. These results provide evidence for the role of AIM2 in the progression of cSCC and identify AIM2 inflammasome function as a potential therapeutic target in these invasive and metastatic tumors.

Markers of cutaneous human papillomavirus infection in individuals with tumor-free skin, actinic keratoses, and squamous cell carcinoma.

Separately, actinic keratosis (AK) and cutaneous squamous cell carcinoma (SCC) have been associated with cutaneous human papillomavirus (HPV) infections. To further explore the association between HPV infection and SCC development, we determined markers of cutaneous HPV infection within a single population in persons with precursor lesions (AK), cancerous lesions (SCC), and without. Serum and plucked eyebrow hairs were collected from 57 tumor-free controls, 126 AK, and 64 SCC cases. Presence of HPV L1 and E6 seroreactivity and viral DNA were determined for HPV types 5, 8, 15, 16, 20, 24, and 38. Significant positive associations with increasing severity of the lesions (controls, AK, and SCC, respectively) were observed for overall HPV L1 seropositivity (13%, 26%, and 37%) and for HPV8 (4%, 17%, and 30%). In parallel, the proportion of L1 seropositive individuals against multiple HPV types increased from 14% to 39% and 45%. The overall E6 seroreactivity, however, tended to decline with AK and SCC, especially for HPV8 (21%, 11%, and 2%). HPV DNA positivity was most prevalent in the AK cases (54%) compared with the SCC cases (44%) and the tumor-free controls (40%). Among all participants, there was a positive trend between overall HPV DNA positivity and L1 seropositivity, but not E6 seropositivity. Taken together, our data suggest that cutaneous HPV infections accompanied by detectable HPV DNA in eyebrow hairs and HPV L1 seropositivity, but not E6 seropositivity, are associated with an increased risk of AK and SCC.

Monochloroacetic acid application is an effective alternative to cryotherapy for common and plantar warts in primary care: a randomized controlled trial.

Cryotherapy and salicylic acid (SA) often fail as treatments for skin warts. We examined the effectiveness of monochloroacetic acid (MCA) for patients with common or plantar warts. Consecutive patients aged 4 years and older with one or more newly diagnosed common or plantar warts were recruited in 53 Dutch general practices. We randomly allocated eligible patients to 13-week treatment protocols of office-applied MCA versus liquid nitrogen cryotherapy every 2 weeks for patients with common warts (n=188), and MCA versus cryotherapy combined with daily SA self-application for patients with plantar warts (n=227). The primary outcome was the proportion of patients whose warts were all cured at 13 weeks. In the common wart group, cure rates were 40/92 (43%, 95% confidence interval 34-54) for MCA and 50/93 (54%, 44-64) for cryotherapy (risk difference (RD) -10%, -25-4.0, P=0.16). In the plantar wart group, cure rates were 49/106 (46%, 37-56) for MCA and 45/115 (39%, 31-48) for cryotherapy combined with SA (RD 7.1, 5.9-20, P=0.29). For common warts, MCA is an effective alternative to cryotherapy to avoid pain during the treatment, although pain after the treatment is similar. For plantar warts, office-applied MCA may be preferred over cryotherapy combined with SA, on the basis of comparable effectiveness, less treatment pain, and less treatment burden.

Randomized clinical trials for psoriasis 1977-2000: the EDEN survey.

This study aims to describe the range of treatment comparisons, study designs and quality of reporting of randomized clinical trials (RCTs) in psoriasis published in a variety of medical and dermatological journals, and to analyze time trends with quality items. Hand-searching of clinical trials of psoriasis published from 1977 to 2000 in 13 medical or dermatological journals, selected as relevant to a European readership, was performed. A total of 249 trials published in 226 papers were classified as RCTs. Of these, 139 (55.8%) employed a parallel control group design, 107 (43.0%) studies adopted a self-control design and 3 (1.2%) a cross-over design. The median number of patients recruited per study was 40 (range 6-699). Overall, 55 different treatment modalities, including topical, ultraviolet-based, systemic, and other miscellaneous therapies were assessed. Only 31 (12.5%) RCTs were comparative studies of treatment modalities in different therapeutic classes. Most of the studies were short-term with a median study duration of 7 weeks (range 1-104), with only 18 studies (7.2%) lasting for more than four months. A variety of outcome measures including 44 different score systems were employed. According to the conclusions of the authors, 196 (78.7%) studies were judged to provide striking or definite observations in favor of one of the treatments examined. No important variations over time were documented for quality items. Based on our survey we have identified an enormous range of treatments that have been evaluated for psoriasis over the examined period. Most studies were short-term, and only a handful compared treatment options in different therapeutic classes. Since we did not examine all the relevant journals, the number of treatment options may be even greater than we have documented. There is an urgent need to reset the research agenda focusing on long-term comparative RCTs. Editors of major medical and dermatological journals are urged to take a role in improving the quality of RCT reporting.

Sunlight exposure and (sero)prevalence of epidermodysplasia verruciformis-associated human papillomavirus.

Ultraviolet radiation (UVR) is associated with an increased risk of squamous cell carcinoma (SCC), which is in part due to immunomodulation. In addition, human papilloma virus (HPV), especially the epidermodysplasia verruciformis (EV)-associated types, may be involved. In view of the capacity of UVR to impair host resistance to infections, we investigated the relationship between solar exposure and the prevalence of cutaneous HPV. In a case-control study on skin cancer (320 controls and 156 patients) a lifetime-retrospective questionnaire on sun exposure was administered. The presence of DNA of HPV types 5, 8, 15, 20, 24, and 38 in plucked eyebrow hair and type-specific seroreactivity were assessed and analyzed in relation to estimated exposure. Sunburn episodes in the past, especially at age 13-20 y, appeared to be associated with an enhanced risk of EV-HPV DNA positivity. In contrast, a higher lifetime sun exposure was associated with a lower risk of HPV infection. These results indicate that UVR at erythematogenic doses increases the risk of EV-HPV infection, possibly due to impaired host resistance to HPV and/or a direct effect of UVR on viral replication. The favorable association between lifetime sun exposure and HPV prevalence, however, underscores the enigmatic role of HPV in skin carcinogenesis.

Skin diseases among schoolchildren in Ghana, Gabon, and Rwanda.

OBJECTIVES: Skin diseases, especially skin infections, among schoolchildren in Africa can be a major health problem. The objective of this study was to determine the prevalences of skin diseases among children in rural and urban schools in three different African countries and to study the influence of socioeconomic level. METHODS: Cross-sectional, population-based studies were performed in Ghana, Gabon, and Rwanda. Point prevalences of skin diseases were estimated on the basis of physical examination by at least one dermatologist. RESULTS: A total of 4839 schoolchildren were seen. The overall prevalence of schoolchildren with any skin disease was high and amounted to 34.6% and 42.0% in two Ghanaian studies, 45.8% in Gabon, and 26.7% in Rwanda. In children with skin diseases, skin infections represented the greatest proportion of disease, accounting for 14.7% and 17.6% of skin disease in the Ghanaian studies, and 27.7% and 22.7% in Gabon and Rwanda, respectively. Diseases with the highest prevalence were tinea capitis and bacterial skin infections, especially in rural areas and in schools serving children living at lower socioeconomic levels. CONCLUSIONS: The prevalences of skin diseases among African schoolchildren were high. Skin infections such as tinea capitis and pyoderma predominated.

HPV type in plantar warts influences natural course and treatment response: secondary analysis of a randomised controlled trial.

BACKGROUND: Cryotherapy is effective for common warts, but for plantar warts available treatments often fail. OBJECTIVES: Within a pragmatic randomised controlled trial, we examined whether subgroups of common and plantar warts have a favourable natural course or response to treatment based on wart-associated HPV type. STUDY DESIGN: Consecutive patients with new common or plantar warts were recruited in 30 Dutch family practices. Patients (n=250) were randomly allocated to liquid-nitrogen cryotherapy, 40% salicylic acid self-application, or wait-and-see policy. Before treatment, swabs were taken from all separate warts and analysed by a broad spectrum HPV genotyping assay. At 13 weeks, cure rates with 95% confidence intervals of common and plantar warts on intention to treat basis were compared between treatment arms for the different wart-associated HPV types. RESULTS: In total, 7% of swabs tested negative for HPV DNA and 16% contained multiple types, leaving 278 of 371 common swabs (75%) and 299 of 373 plantar swabs (80%) with a single type for analysis. After wait-and-see policy, cure rates were 2/70 (3%, 95% confidence interval 1-10) for HPV 2/27/57-associated common warts, 4/58 (7%, 3-16) for HPV 2/27/57-associated plantar warts, and 21/36 (58%, 42-73) for HPV 1-associated plantar warts. After cryotherapy, cure rates were 30/44 (68%, 53-80), 6/56 (11%, 5-21), and 15/23 (65%, 45-81); after salicylic acid 16/87 (18%, 12-28), 15/60 (25%, 16-37), and 24/26 (92%, 76-98), respectively. CONCLUSIONS: HPV type influenced the natural course and response to treatment for plantar warts. HPV testing potentially optimises wart treatment in primary care.

No acceleration of UV-induced skin carcinogenesis from evenly spread dietary intake of cyclosporine in contrast to oral bolus dosages.

BACKGROUND: Organ transplant recipients using the immunosuppressant cyclosporine have an increased risk for developing nonmelanoma skin cancer. Disparate effects of cyclosporine have, however, been reported on UV-induced skin carcinogenesis in mouse experiments. Therefore, we set out to compare three experimental protocols using mice, with the aim to emulate most closely the increased skin cancer risk in organ transplant recipients. METHODS: UV carcinogenesis was performed in hairless SKH-1 mice by three protocols: dietary cyclosporine and daily UV exposures, dietary cyclosporine after a period of UV exposures, and bolus dosing cyclosporine by gavage and repeated UV exposures. RESULTS: Using chronic UV exposure, continuous dietary administration of cyclosporine was shown to inhibit tumor formation. Dietary cyclosporine after a period of UV exposures did not affect ensuing UV carcinogenesis. However, in contrast with dietary cyclosporine, bolus dosages of cyclosporine by gavage, resulting in strongly varying blood levels of cyclosporine, increased tumor development in chronically UV-exposed mice. There was no difference in tumor development between mice UV-irradiated during peak or trough levels of cyclosporine in the blood. Time-averaged levels in these mice were similar to those with cyclosporine in the diet. CONCLUSIONS: Cyclosporine in bolus doses appears to increase skin cancer development, whereas cyclosporine administration more evenly spread over time does not. Extrapolation to transplant patients suggests that the mode of administrating cyclosporine may be crucial for the increased skin cancer risk and that this risk might be lowered with a more steady release of cyclosporine in the body.

Human papillomavirus load in eyebrow hair follicles and risk of cutaneous squamous cell carcinoma.

BACKGROUND: Beta-human papillomavirus (betaPV) may play a role in the development of cutaneous squamous cell carcinoma (SCC). However betaPV is highly prevalent, and it may only be people with a higher viral load who have increased risk of SCCs. We therefore examined the association between betaPV load and SCCs. METHODS: We recruited 448 immunocompetent cases with SCCs and 464 controls from Italy and Australia and 497 immunosuppressed organ transplant recipients (OTR; 179 cases and 318 controls) from Europe. We used reverse hybridization to genotype 25 betaPV types in eyebrow hair follicles and determined the viral load for eight selected types using quantitative PCR. We used logistic regression to assess associations between type-specific and cumulative viral load and SCCs. RESULTS: Australian and OTR participants in the highest cumulative load tertile were at significantly higher risk of SCCs than those in the lowest tertile. Those with more than four betaPV types in the high load tertile were at approximately three-fold increased risk of SCCs. In Australia, HPV23 and 36 loads were significantly associated with SCCs, with borderline associations for HPV5 and 38. In OTR, HPV8 and 38 loads were significantly associated and HPV20 and 36 were borderline. We found little evidence for an association between load and SCCs in Italy. CONCLUSIONS: High viral load may be associated with risk of cutaneous SCCs, with total load seemingly more important than the load of any specific type. IMPACT: Our findings lend weight to the hypothesis that HPV plays a role in skin carcinogenesis.

Cutaneous wart-associated HPV types: prevalence and relation with patient characteristics.

BACKGROUND: Epidemiological data on cutaneous wart-associated HPV types are rare. OBJECTIVES: To examine the prevalence of cutaneous wart-associated HPV types and their relation with patient characteristics. STUDY DESIGN: Swabs were taken from all 744 warts of 246 consecutive immunocompetent participants and analysed by a broad spectrum HSL-PCR/MPG assay. Patient details including location, duration, and number of warts were recorded. RESULTS: No HPV DNA was detected in 49 (7%) swabs, a single HPV type in 577 (78%) swabs, and multiple HPV types in 118 (16%) swabs. HPV 2, 27 and 57 (alpha genus), HPV 4 (gamma genus) and HPV 1 (mu genus) were the most frequently detected HPV types, and HPV 63 (mu genus) was only frequently detected together with other HPV types. Less frequently detected HPV types were HPV 3, 7, 10 and 28 (alpha genus), 65, 88 and 95 (gamma genus) and 41 (nu genus). Warts containing HPV 1 showed the most distinct clinical profile, being related to children aged <12 years, plantar location, duration <6 months, and to patients with <4 warts. CONCLUSIONS: HPV 27, 57, 2 and 1 are the most prevalent HPV types in cutaneous warts in general population. Warts infected with HPV 1 have a distinct clinical profile.

Genus beta human papillomaviruses and incidence of basal cell and squamous cell carcinomas of skin: population based case-control study.

OBJECTIVE: To investigate the association between genus beta human papillomaviruses and the incidence of non-melanocytic skin cancer in the general population. DESIGN: Population based case-control study. SETTING: New Hampshire, USA. PARTICIPANTS: 2366 skin cancer cases and controls from the general population aged 25 to 74 years (663 squamous cell carcinoma, 898 basal cell carcinoma, 805 controls), with plasma samples tested for L1 antibodies to 16 genus beta human papillomaviruses by multiplex serology. MAIN OUTCOME MEASURES: Odds ratios for squamous cell carcinoma and basal cell carcinoma associated with seropositivity to beta human papillomaviruses. RESULTS: Squamous cell carcinoma, but not basal cell carcinoma, cases had a higher prevalence of each of the individual beta human papillomaviruses assayed compared with controls. The odds ratios for squamous cell carcinoma increased with the number of beta types positive (odds ratio for one type positive 0.99 (95% confidence interval 0.74 to 1.33); two to three types positive 1.44 (1.03 to 2.01); four to eight types positive 1.51 (1.03 to 2.20); more than eight types positive 1.71 (1.12 to 2.62); P for trend (categorical)<0.001; P for trend (continuous)=0.003). With limited statistical power, the association was stronger among long term users of systemic glucocorticoids (odds ratio 3.21, 1.22 to 8.44) than among non-users (1.23, 0.97 to 1.55). CONCLUSIONS: These findings support a relation between genus beta human papillomavirus infection and the incidence of squamous cell carcinoma of the skin in the general population, as well as potential enhancement of risk by immunosuppression.

Betapapillomaviruses frequently persist in the skin of healthy individuals.

Infections with human papillomaviruses (HPVs) belonging to the genus Betapapillomavirus have been linked to the development of non-melanoma skin cancer. Although persistence is expected, systematic investigation of this aspect of betapapillomavirus (beta-PV) infection has not been conducted. This study investigated the prevalence and persistence of 25 known beta-PV types in the skin of immunocompetent individuals. Over a 2 year period, eight consecutive plucked eyebrow hair samples taken from 23 healthy individuals were analysed for the presence of beta-PV DNA. Using a recently published general beta-PV PCR and genotyping method, 61% of the individuals were beta-PV DNA positive for one or more types at intake, whereas during follow-up this percentage rose to 96%. HPV23 was the most frequently detected beta-PV type. Type-specific beta-PV DNA was detected over 6 months or longer in 74% of the individuals. In 57% of the individuals, DNA from multiple beta-PV types was detected simultaneously for 6 months or longer. When the detection intervals of all beta-PV type-specific infections in the study population were considered, a substantial proportion, 48%, lasted at least half a year. The consistent beta-PV patterns found over time in most individuals strongly suggested that beta-PV DNA detection in plucked eyebrow hairs reveals true beta-PV infection. If the minimum interval of detection was set at 6 months, persistent beta-PV infections were found in the majority of the study population (74%).