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Journal of Virology, January 2009, p. 811-816, Vol. 83, No. 2
0022-538X/09/$08.00+0 doi:10.1128/JVI.01338-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
Intrafamilial Transmission and Family-Specific Spectra of Cutaneous Betapapillomaviruses
S. J. Weissenborn,1*
M. N. C. De Koning,2
U. Wieland,1
W. G. V. Quint,2 and
H. J. Pfister1
Institute of Virology, University of Cologne, Fuerst-Pueckler-Str. 56, 50935 Cologne, Germany,1
DDL Diagnostic Laboratory, Voorburg, The Netherlands2
Received 26 June 2008/
Accepted 29 October 2008

ABSTRACT
Cutaneous human betapapillomaviruses (beta-HPVs) are widespread
in the general population and have been associated with skin
cancer. To evaluate the impact of continuous person-to-person
contact within families on an individual's beta-HPV type spectrum,
we collected serial skin swab samples from parents and children
from 10 families. All participants were found to be beta-HPV
DNA positive, with 1 to 13 types at study entry (median, 4.0
types). Initial and cumulative (2 to 16 types) HPV type multiplicities
varied widely between different families but only a little between
family members. The high intrafamilial correlation of HPV multiplicity
is already obvious for babies aged 10 days to 10 months. Family
members typically displayed similar spectra of HPV types. More
than 75% of the HPV types in babies were also detected in their
parents. This indicates that HPV transmission mainly results
from close contact between family members. Type-specific persistence
for at least 9 months was more prevalent in parents (92%) than
in children (66%). Of the types detected throughout the study,
24% turned out to persist in the parents and only 11% in the
children. Interestingly, about one-half of the HPV types found
to persist in one of the parents occurred less frequently or
even only sporadically in the spouse. Similarly, only one-third
of the persisting parental types also persisted in their children.
This indicates that even regular exposure to cutaneous HPV does
not necessarily lead to the establishment of a persistent infection,
which may point to type-specific susceptibilities of different
individuals.

INTRODUCTION
Cutaneous human papillomaviruses (HPV) cluster in the genera
Betapapillomavirus (beta-HPV),
Gammapapillomavirus, Mupapillomavirus,
and
Nupapillomavirus of the family
Papillomaviridae, and several
types are classified in genus
Alphapapillomavirus together with
mostly mucosal types (
7). Common, plantar, and flat warts are
induced by representatives of genera
Alphapapillomavirus, Gammapapillomavirus, Mupapillomavirus, and
Nupapillomavirus most frequently in children
and adolescents 12 to 16 years of age (
13). Beta-HPV causes
flat warts and red-brown plaque-like and pityriasis versicolor-like
lesions in patients with epidermodysplasia verruciformis but
no characteristic pathology in the general population (
14).
Clinically inapparent infections by members of genera beta-HPV
and
Gammapapillomavirus have been found to be extremely widespread
in the general population when testing skin swabs or plucked
eyebrow hairs for HPV DNA (
1,
3,
4). These HPV types seem to
be acquired already in the first days of life (
2), but everybody
will be exposed throughout life to multiple beta-HPV and gamma-HPV
types in view of their high prevalence.
Follow-up studies showed that a part of the transmitted HPV is able to establish persistent infections in the new host. Type-specific persistence was observed over 5 to 7 years in forehead skin and for up to 24 months in eyebrow hairs (6, 10).
Beta-HPVs deserve special interest because of compelling evidence for the carcinogenicity of beta-HPV types 5 and 8 in the skin of patients with epidermodysplasia verruciformis and because of growing evidence for the carcinogenicity of beta-HPV in the skin in general (12). Beta-HPV DNA was detected in up to 85% of precancerous actinic keratoses (15), in 30% to 50% of cutaneous squamous cell carcinomas of immunocompetent patients, and in up to 90% of cutaneous squamous cell carcinomas of immunosuppressed patients (reviewed in reference 14).
We became interested in the impact of continuous person-to-person contact within a family on an individual's beta-HPV type spectrum. To address this question, we collected serial samples from the foreheads, the backs of the hands, and the buttocks of parents and children. Since young children were involved, easy and painless skin swabs were used as study material instead of plucked hairs. To ensure a comprehensive and sensitive analysis, we chose a recent HPV detection and typing method which allows the parallel identification of the 25 established betapapillomavirus (beta-PV) genotypes (5).

MATERIALS AND METHODS
Study population.
Ten families with young children voluntarily applied to participate
in this study after local announcement. The study population
comprised 40 individuals: 14 children (median age at study entry,
9.6 months; range, 10 days to 8.6 years), 10 mothers (median
age, 31.5 years; range, 29.1 to 44.5 years), 10 fathers (median
age, 33.2 years; range, 25.9 to 44.5 years), and 6 grandparents
(median age, 65.8 years; range, 57.3 to 77.8 years). The sampling
period spanned a mean of 13.7 months (range, 0 to 28.5 months),
with a median of 4.4 sampling episodes (range, 1 to 9 episodes).
Altogether 484 swab samples from the forehead, back of the right
hand, and right side of the buttock were collected. The study
protocol was approved by the ethics review board of the University
of Cologne, and the study was conducted according to the Declaration
of Helsinki principles. The parents gave written informed consent
to participate in the study and answered a questionnaire about
the presence/absence of psoriasis or neurodermatitis or other
acute or chronic diseases. No diseases were present in any of
the participants, and none of them suffered from clinically
apparent warts. Samples were assigned pseudonyms, and all analyses
were performed blinded to any information about the samples.
Test procedures.
Tubes including wood sticks with cotton (PS swab tube; Greiner Bio-One, Solingen, Germany) and filled with 2 ml phosphate-buffered saline (PBS) were used for swab sampling. Samples within one family were taken by one or both of the parents. Participants were advised to take samples in the evening. Swabs were soaked in saline solution (PBS) and first used to moisten a skin area of 4 by 5 cm. After 1 minute, swabs were firmly drawn back and forth 15 times over the moistened area and then suspended in the remaining PBS. The samples were stored at 4°C and processed within 72 h. Suspensions were centrifuged at 14,000 x g for 5 min, and DNA extraction of pellets (QIAamp DNA minikit; Qiagen, Hilden, Germany) was carried out according to the manufacturer's protocol. Beta-HPV detection and genotyping were carried out by a broad-spectrum PCR with subsequent analysis of amplimers with a reverse hybridization assay that permitted specific detection and identification of the 25 established beta-PV genotypes as described previously (5).
Statistical analysis.
All analyses (Pearson test, paired t test) were performed two-sided using SPSS 15.0 (SPSS Inc., Chicago, IL).

RESULTS
HPV DNA prevalence and multiplicity in cutaneous swabs.
All 40 participants of this study were found to be beta-HPV
DNA positive, although to highly variable degrees. The positivity
rates of the samples from different individuals ranged from
7 to 97%. Considering site-specific prevalence per individual,
HPV positivity was on average higher on samples from the forehead
(79%) and the back of the hand (81%) than on those from the
buttock (64%). One to 13 HPV types were detected per individual
in the three swabs taken at study entry (median, 4.0 types),
and the cumulative HPV type multiplicity over all samples from
a participant ranged from 1 to 16 types (Fig.
1).
The HPV type multiplicity varied widely between different families
(2 to 18 types), but only a little between family members (Fig.
1). For example, high HPV type multiplicities could be observed
for all members of families 2 and 7, with 12 to 15 and 11 to
13 HPV types, respectively (Fig.
1). In contrast, all members
of family 5 had low type multiplicities (one to five types).
There was some concern that differences in multiplicity between
families were related to systematic differences in sampling.
Despite the specified protocol, the intensity of swabbing and
the size of the swabbed area may have varied between the different
families, and this may have resulted in differences in the number
of squames and cells per swab. We therefore tested whether type
multiplicity correlated with the amount of cellular DNA but
observed no such correlation (
R = –0.059; paired
t test)
in 28 randomly chosen samples. When the samples were divided
into three equally large groups according to cellular DNA input,
the positivity rates of the 18 specific types present in these
swabs did not appear to differ between these groups. Even HPV
types with low prevalence could be detected in the group with
the smallest amount of cellular DNA. Furthermore, no impact
of the individual sampling procedure on HPV multiplicity was
observed after two individuals from families with low type multiplicities
were swabbed by an individual who obtained a high type multiplicity
by self-swabbing (data not shown). This experiment suggests
additionally that the sampling technique is not prone to contamination
by the person taking the swab. Altogether, these observations
indicate that the characteristic HPV multiplicities observed
for different families are not biased by self-sampling.
To compare the prevalences of specific HPV types in the study population, we considered only the samples from parents and their youngest children taken at study entry to avoid any bias due to different numbers of family members and samples per participant. The most prevalent HPV types were 93, 23, 17, 76, 9, 24, 38, and 36 in ascending sequence (15.6% to 34.4%).
It was most interesting to note that the high intrafamilial correlation of HPV type multiplicity is already obvious for babies aged 10 days to 10 months (babies versus mothers: R = 0.915, P = 0.001; babies versus fathers: R = 0.662, P = 0.07; Pearson test). All the babies showed at least 1 beta-HPV type and up to 10 different beta-HPV types in their first swabs (Table 1). More than 75% of the HPV types detected in babies were also detected in at least one of their parents. Specifically, six of eight HPV types detected in the 10-day-old baby were found in its mother or father.
HPV persistence and family-specific beta-HPV spectra.
HPV persistence could be analyzed in parents and all children
of six families (families 2, 3, 4, 5, 7, and 9) for whom samples
from at least four points in time and a follow-up period of
at least nine months were available (mean follow-up time: 17.7
months; range, 9 to 28.5 months; mean number of time points,
6.0; range, 4 to 9 time points). Type-specific persistence was
defined as HPV DNA being site specifically detectable in more
than two-thirds of the samples or over 9 months with at most
one negative sample in between. HPV types found in less than
20% of samples were defined as sporadic. Of the infections classified
as sporadic, 38% occurred on the back of the hand, 36% on the
forehead, and 26% on the buttocks. Persistent HPV types could
be observed in 92% of 12 adults and 66% of 9 children, with
a maximum of 6 types and a median of 2.5 HPV types in parents
and 1.0 HPV type in children (Fig.
1). This corresponds on average
to 30% of the detectable HPV types in parents and to 12% in
children.
Overall, one-half of the persisting HPV types differed between the parents of a family. In family 2 (Fig. 2), HPV types 17, 24, and 76 fulfilled the definition of persistence, both in the father and mother, whereas HPV types 5, 9, and 93 appear to persist only in the mother. The persistent HPV types 5, 9, 24, and 93 found on the mother were furthermore detected on both parents of the mother. For the father of family 4 (Fig. 3), HPV types 20, 36, 38, and 96 could be identified as persistent. The mother persistently harbored HPV types 15 and 38. Thus, except for type 38, different HPV types persisted in the parents. HPV types 20, 36, and 96, persistently detected on the father, were only sporadically detected in swabs from the mother. HPV type 15, which persists on the mother, was also detected in 7 of 27 swabs from the father. Five of eight HPV types frequently or persistently detected in the father or mother were also detected in the respective grandparents (Fig. 1).
Eleven out of 13 HPV types that were found to persist in children
of all age groups were also persistently detected in at least
one of the parents. No child had a persistent type that was
only sporadically present or not present in the parents. However,
not all persistent HPV types on the parents were persistent
on children, too. HPV types 17, 24, and 76, which persist on
both parents of family 2, were also persistently found in the
child. In contrast, types 5, 9, and 93 were not persistently
detected on the child even though they dominated in one of the
parents. For the child of family 4, the only persisting HPV
type was 38, which is the only common persistent type found
on the parents.
Several HPV types appeared to be clearly overrepresented in the samples from families 2, 3, 4, 7, and 9 (Fig. 1) compared to the samples collected at study entry from parents and the youngest children of the nine other families. For instance, in family 2, the prevalence ratios of HPV types 5, 17, 24, 76, and 93 were 4.5 (49% versus 11%), 4.4 (71% versus 16%), 3.9 (78% versus 20%), 3.9 (67% versus 17%), and 3.1 (50% versus 16%), respectively. The impression of family-specific spectra is further supported by the fact that HPV types which are prevalent in general may be underrepresented in specific families, e.g., type 36 in family 2 (13% versus 34%) and types 17, 24, 76, and 93 in family 4 (0% versus 16%, 2% versus 20%, 4% versus 17%, and 4% versus 16%, respectively).

DISCUSSION
This study describes the first comprehensive analysis of beta-HPV
spectra in healthy families. We observed a high HPV DNA prevalence
and often a high type multiplicity on the skin, which increased
with the number of samples analyzed. The type multiplicities
found here, with up to 13 different types at a single point
in time, exceed the numbers observed in earlier studies, which
differed in methods and material. Antonsson et al. (
1) also
analyzed multiple skin swabs of both healthy individuals and
dialysis patients but used a different primer set for PCR and
typed by sequencing 4 to 10 clones of PCR products of each sample.
They found up to seven different HPV types or type candidates
per individual. It can be assumed that more HPV types would
have been found if additional clones had been analyzed. de Koning
et al. (
6) used the detection and typing method applied in this
study but analyzed eight samples of 8 to 10 plucked eyebrow
hairs collected over 2 years from 23 adults. They observed a
maximum number of six to nine types at different time points
and median HPV type multiplicities ranging from 0.5 to 2. When
comparing these data with a maximum of 13 different types and
a median of 4.0 types in the current study, it must be realized
that detection of HPV DNA in plucked hairs and skin swabs reflects
to different degrees either established infections, transient
infections, or just surface contamination. Hair follicles have
been proposed as a possible reservoir of beta-HPV (reviewed
in reference
14), and thus HPV detection in follicles more likely
reflects persistent infections. In contrast, in the interfollicular
epidermis one may expect a higher proportion of transient infections.
Furthermore, rather large skin areas are sampled by swabbing,
which makes this material more sensitive to surface contamination
than plucked hairs. By the analysis of swabs, it is not possible
to distinguish between an established infection and surface
contamination in individual cases.
An established infection appears to be more likely if a type is repeatedly detected in consecutive swabs. We therefore used a very stringent definition for HPV DNA persistence: the DNA must be site specifically detectable in more than two-thirds of the samples or over 9 months with at most one negative sample in between. According to this definition, two-thirds of the children and more than 90% of the adults had at least one persistent HPV type. de Koning et al. (6) showed type-specific persistence of beta-HPV in consecutively plucked eyebrow hairs for at least one-half of a year in 74% of adults.
Different families showed characteristic HPV multiplicities, both when sporadically detected HPV types are included and when they are excluded. Furthermore, similar type spectra among family members allowed the identification of family-specific HPV types. These findings most likely reflect continuous HPV transmission by close direct contact between family members and via virus-contaminated surfaces in the common household. High multiplicities in specific families may result from a high multiplicity in at least one of the parents.
As noted before (2), beta-HPV was already detectable on the skin of children in the first months of life. In babies less than 1 month old, detection of beta-HPV DNA in skin swabs primarily reflects exposure and not-yet-established infections (2). In the current study, all children who were less than 1 year old already showed a type multiplicity strongly correlated with that of their parents. Finding the vast majority of HPV types from the children also in one or both parents strongly argues for a predominantly intrafamilial transmission. A few HPV types that were present on infants and not on parents may have been transmitted from other contact persons such as nurses or grandparents or may just have escaped detection in parents at study entry.
HPV types detected sporadically in any family member mostly occurred only sporadically or not at all in other members of that family. In about 30% of the cases sporadic HPV types in one family member were found more frequently or even persistently in at least one other family member. Sporadically detected HPV types may therefore result from transmission within the family but may also be from outside.
It was interesting that about one-half of the HPV types found to persist in one of the parents occurred less frequently or even only sporadically in the spouse. This indicates that even continuous transmission of cutaneous HPV over years through close physical contact does not necessarily result in a persistent or at least frequently detected infection in spouses. Similarly, only a fraction of HPV types found persistently in one of the parents established a persistent infection in the children. On the other hand, HPV types 20 and 92 were persistently detected in the child of family 7 and only less frequently in the parents. This is consistent with finding unique beta-PV profiles in plucked-hair samples from individuals sharing a student household for 6 to 12 months (6). Although the contact with non-family members is in general certainly less intense than that within families, one may nevertheless expect a regular exposure to cutaneous HPV. In certain families of this study we could even confirm exposure to several prevalent HPV types by sporadic detection without finding evidence for persistent infections.
There are numerous examples of HPV types that are abundant in one individual of a common household but only infrequently detected on other family members. This may point to type-specific beta-HPV susceptibility of different individuals. This concept would be in line with finding individual-specific HPV types in different immunosuppressed renal transplant recipients, which prevail in multiple benign and malignant lesions located on various anatomical sites and partially removed up to 7 years apart (8, 9, 11).
There are no data so far on a molecular basis of type-specific susceptibility. Intracellular or intercellular control mechanisms for the replication and transcription of the viral genome and the activity of viral proteins, as well as immune reactions against HPV-harboring cells, may be responsible. Individual immunologic determinants such as HLA alleles may be of major importance for the clearance of inapparent or overt HPV infections. It would be interesting to analyze possible correlations between host genetics and individual spectra of persisting beta-HPV types.

ACKNOWLEDGMENTS
We thank Monika Junk for excellent technical assistance and
W. Lehmacher, H. Christ, and Z. Tolman for helpful discussions.
Furthermore, we are very much obliged to the families who participated
in this study.

FOOTNOTES
* Corresponding author. Mailing address: Institute of Virology, University of Cologne, Fuerst-Pueckler-Str. 56, 50935 Cologne, Germany. Phone: 49 221 4783911. Fax: 49 221 4783904. E-mail:
Soenke.Weissenborn{at}uk-koeln.de 
Published ahead of print on 5 November 2008. 

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Journal of Virology, January 2009, p. 811-816, Vol. 83, No. 2
0022-538X/09/$08.00+0 doi:10.1128/JVI.01338-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
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