Critical Reviews http://cro.sagepub.com/ in Oral Biology & Medicine Human Papillomavirus Infections in Children: the Potential Role of Maternal Transmission Stina Syrjanen and Mirja Puranen CROBM 2000 11: 259 DOI: 10.1177/10454411000110020801 The online version of this article can be found at: http://cro.sagepub.com/content/11/2/259 Published by: http://www.sagepublications.com On behalf of: International and American Associations for Dental Research Additional services and information for Critical Reviews in Oral Biology & Medicine can be found at: Email Alerts: http://cro.sagepub.com/cgi/alerts Subscriptions: http://cro.sagepub.com/subscriptions Reprints: http://www.sagepub.com/journalsReprints.nav Permissions: http://www.sagepub.com/journalsPermissions.nav >> Version of Record - Jan 1, 2000 What is This? Downloaded from cro.sagepub.com by guest on August 22, 2014 For personal use only. No other uses without permission. HUMAN PAPILLOMAVIRUS INFECTIONS IN CHILDREN: THE POTENTIAL ROLE OF MATERNAL TRANSMISSION Stina Syripinen* Mira Puronen Department of Oral Pathology and Radiology, Institute of Dentistry, Lemminkaisenkatu 2, FIN-20520 Turku, Finland; and MediCity Research Laboratory, Facully of Medicine, University of Turku, Finland; *corresponding author, [email protected] ABSTRACT: To date, more than 100 types of human papillomavirus (HPV) have been identified. In the past 20 years, there has been an increasing interest in HPVs because of their potential role in the pathogenesis of malignant tumors. HPV infections are known to affect predominantly adult, sexually active age groups, whereas skin warts, at various anatomic sites, are usually associated with younger individuals. The modes of viral transmission in children remain controversial, including perinatal transmission, auto- and hetero-inoculation, sexual abuse, and, possibly, indirect transmission via fomites. Recent studies on perinatal infection with HPV have been inconclusive. It is still unclear how frequently perinatal infection progresses to clinical lesions, whether genital, laryngeal, or oral. Conflicting reports have been published on the prevalence of HPV infections in children. The current consensus is, however, that newborn babies can be exposed to cervical HPV infection of the mother. The detection rate of HPV DNA in oral swabs of newborn babies varies from 4% to 87%. The concordance of HPV types detected in newborn babies and their mothers is in the range of 57% to 69%, indicating that the infants might acquire the HPV infection post-natally from a variety of sources. HPV antibodies have been detected in 10% to 57% of the children, and there is usually no correlation between seropositivity and the detection of HPV DNA in either the oral or the genital mucosa. There is also evidence that transmission in utero or post-natal acquisition is possible. The mode of in utero transmission remains unknown, but theoretically the virus could be acquired hematogenously, by semen at fertilization, or as an ascending infection in the mother. The understanding of viral transmission routes is important, particularly because several vaccination programs are being planned worldwide. The serologic response to HPV detected in different populations of young women or women at risk of cervical cancer might be due to genital infections, but the possibility that HPV infection has been acquired earlier in life through the oral mucosa or respiratory tract cannot be ruled out. Key words. Human papillomavirus, HPV transmission, child, infant, mouth, vertical transmission. (1) Introduction Human papillomaviruses (HPVs) are DNA viruses that can induce hyperplastic, papillomatous, and verrucous squamous cell lesions in the skin and at various mucosal sites. HPV infections are widespread and occur worldwide. Today, the plurality of HPVs is well-established; more than 100 HPV types have been identified. HPVs have gained increasing interest because of their potential role in the pathogenesis of malignant tumors. Both low-risk and high-risk HPV types exist-the latter constituting a significant risk for cervical pre-cancerous lesions and cervical cancer. Recently, HPVs have been implicated in oral, laryngeal, and esophageal carcinogenesis, though the evidence is as yet less convincing than that for cervical cancer (Miller and White, 1996; Snijders et al., 1997; Syrjanen, 1997b,c). The biologic behavior of HPV infection is unpredictable, and more data are needed before the synergistic factors involved in these HPV-associated diseases can be identified. While genital HPV infections seem to affect predominantly adult, sexually active age groups, skin warts at various anatomic sites have been characteristically regarded as a disease affecting children. Apart from these cutaneous HPV lesions, HPV infections of the oral mucosa, and particularly those of the larynx, seem to be typical pediatric diseases as well. More recently, HPV infections have also been described in the nasal mucosa and genital tract of children (De long et al., 1982; Sundararaj et al., 1991; Handley et al., 1993a,b; Obalek et al., 1993; Alberico et al., 1995). There is ample evidence that the incidence of anogenital warts in pre-pubertal children is increasing. This increased incidence cannot be entirely attributed to the increased awareness of this disease but reflects a true increase in the incidence of these infections. The modes of viral transmission in children remain important and controversial. Several potential modes of transmission can be theorized for these pediatric HPV infections, including perinatal transmission, auto- and hetero-inoculation, sexual abuse, and, possibly, indirect transmission via fomites. ln the early days, it was thought that all genital warts in children were contagious. Subsequently, childhood sexual abuse was thought to be the most com- Biol Med Oral Biol Rev Oral Crit Rev I l(2):259-274 (2000) (2000)Crit 11(2):259-274 Med Downloaded from cro.sagepub.com by guest on August 22, 2014 For personal use only. No other uses without permission. 259 259 TABLE 1 Modes of HPV Transmission in Children (1) Non-sexual Transmission Directly - from one person to another - auto-inoculation Indirectly - via contaminated objects - via contaminated surface (2) Maternal transmission Directly - during vaginal delivery from the mother - at Caesarean section/early rupture of membranes - from mother when taking care of the baby - via saliva? - via breast milk? Indirectly - during vaginal delivery via contaminated objects or surfaces - when born by Caesarean section via contaminated objects or surfaces Transmission, in utero - through semen - ascending infection from mother's genital tract - transplacentally (3) Sexual abuse mon mode of viral transmission, and HPV types 6 and 11 were found to be the two most prevalent viral types in genital warts of children. However, more recent studies suggest that perinatal infection and auto- or hetero-inoculation may be much more prevalent than previously thought (Armbruster-Moraes et al., 1994; Cason et al., 1995; Puranen et al., 1996a, 1997; Bennett and Powell, 1987). It has been repeatedly documented that HPV type 2 is present in a significant proportion of pediatric anogenital lesions, strongly implicating auto- or heteroinoculation as an important mode of disease transmission. Similarly, the origins of HPV infections in oral and laryngeal mucosa are uncertain, although modes of transmission similar to those proposed for ano-genital HPV infections have been suggested. The present review deals with the different manifestations of HPV infections in children with special emphasis on their potential routes of transmission (Table 1). These data are largely based on,our experience of the biologic behavior of genital HPV infections gained from a long-term (since 1981) cohort study of HPV-infected women, conducted at the University Hospital of Kuopio. During this study, the authors undertook a systematic examination of babies born to these women. We also had access to a large series of tissue samples from upper aerodigestive tract lesions 26 260 (in the oral mucosa, sinonasal mucosa, larynx, lung, esophagus), in which HPV involvement was first suspected by our group in the early 1980s and later confirmed by the detection of HPV DNA in these lesions (Syrjanen and Syrjanen, 1981, 1987; Syrjanen et al., 1983a,b, 1986b, 1987, 1988; Chang et al., 1990; Kellokoski et al., 1992a,b; Hippelainen et al., 1993; Kataja et al., 1993). (2) Clinical Manifestations of HPV Infection (2.1) ORAL HPV INFECTIONS date, major epidemiological studies have been conducted only on genital infections, and thus, the natural history of oral HPV infection has not been well-established. However, several recent studies on adults suggest that HPV infection can also exist as a latent, subclinical, or clinical infection in oral mucosa. In oral mucosa, squamous cell papilloma, condyloma, verruca vulgaris, and focal epithelial hyperplasia (FEH) are well-established benign epithelial lesions with an HPV etiology. Fig. 1 shows a typical, HPV type- l I-positive oral papilloma of a child. Of the over 100 known HPV types, the following 24 types have thus far been detected in oral lesions: 1, 2, 3, 4, 6, 7, 10, 13, 16, 18, 31, 32, 33, 35, 45, 52, 55, 57, 58, 59, 69, 72, and 73. Several comprehensive reviews have recently been published on HPV infections in oral mucosa and/or in the upper aerodigestive tract fof adults To (Scully et al., 1985; Syrjanen, 1987, 1997a,b; Chang et al., 1991; Garlick and Taichman, 1991; Yeudall, 1992; Miller and White, 1996; Praetorius, 1997; Snijders et al., 1997). Only a few studies on oral HPV infections in children have been published, and therefore no reliable preva- lence rates of such infections in children are available. Squamous cell papilloma has been estimated to account for about 7-8% of all oral tumors in children. In a series of 2370 biopsy samples from patients up to 20 years of age, neoplastic lesions accounted for 12% of the samples, and of all neoplastic lesions, papillomas accounted for 28% (Das and Das, 1993). No such prevalence data for oral condylomas or verruca vulgaris are available in children. Using the most sensitive method, polymerase chain-reaction (PCR), investigators have found HPV 6b and HPV 16 DNA in 24% and 19%, respectively, of the oral scrapings taken from 21 pre-school children (0enison -et al., 1990). In ancAher study of .healthy..chi4ldren aged 3 to 7 years, HPV 16 DNA was detected by PCR in 67 of the 142 buccal swabs (47%) (Rice et al., 1996). In our recent series of 98 children (from 0.3 to 11.6 years of age), born to the mothers included in our prospective cohort of 530 women (Puranen et al., 1996a), oral smears were analyzed for the presence of HPV DNA with PCR, followed by Southern blot CrtRvOalBo.e Crit Rev Oral Biol Med Downloaded from cro.sagepub.com by guest on August 22, 2014 For personal use only. No other uses without permission. 1 1(2):259-274 (2000) hybridization (SBH). HPV DNA was present in 31/98 (31.6%) oral scrapings. On clinical examination, normal oral mucosa was found in 25 and 51 children with and without oral HPV infections, respectively. Minor hyperplastic growths of the oral mucosa were discovered in 22/98 children (22.4%), eight of whom (36.4%) had detectable HPV DNA in their oral scrapings One child had an oral papilloma where HPV 16 was detected. HPV 16 infection was also detected in her mother's genital mucosa at delivery (Puranen et al., 1996a). Levy et al. (1998) detected HPV DNA in only 3.7% (6/164) of oral swabs or mouthrinses taken from children aged less than 12 years, while the detection rate in adolescents was 2.1 % (2/96). Positive amplification for HPV was confirmed by direct DNA sequencing. By PCR targeting the LI region of the HPV genome, Koch et al. ( 1997) carried out a study testing a random sample of Danish children, aged 0 to 17 years, for the presence of HPV in the anal region and the oral cavity. Only four of the 249 anal samples and one of 392 oral samples were HPVpositive. The authors concluded that ano-genital types of HPV are not transmitted, to any measurable degree, by non-sexual routes, and that HPV infection occurs mainly later in life, This view, however, is not supported by studies on newborn babies in whom HPV DNA has been detected in 37% to 73% of nasopharyngeal aspirates or buccal swabs (Sedlacek et cil., 1989; Cason et aii, 1992; Fredericks et al., 1993; Pakarian et a l, 1994, Puranen et cl., 1997) This issue is discussed in detail below (see 'MATERNAL, TRANSMISSION ). Similarly, HPV infections of children seem to be common, as identified by HPV serology (10%-46%), as discussed below (see "Detection of Serum Antibodies to HPV"). (2.2) JUVENILE-ONSET LARYNGEAL PAPILLOMAS The most notable characteristic of laryngeal papillomas is their tendency to recur even after a radical surgical excision. The disease is therefore also known as juvenile-onset recurrent respiratory papillomatosis (10-RRP). Re-operations may be indicated at annual intervals or even as frequently as every two weeks (Mounts and Shah, 1984; Kashima et al 1993). The number of operations needed by single JOP patients has been between I and 118. The mean number of operations in 141 patients from three different studies was 13.7 (Cohen et cil, 1980; Abramson et ca, 1987; Padayachee and Prescott, 1993) Another characteristic of laryngeal papillomas is their tendency to regress spontaneously. Remission can be temporary or for the lifetime of the patient, and remission periods of as long as 25 or 30 years have been reported (Abramson et al, 1987; Daya and Gallimore, 1993). Spontaneous remissions have been reported at puberty, and recurrence or increase in the severity of disease during pregnancy (Hirschfield and Steinberg, 1989). (2.3) ANOGENITAL HPV INFECTIONS (2.3.1) Subclinical infections Only a few studies are available on subclinical genital HPV infections in children, In a series of 70 clinically normal foreskins of newborns undergoing routine circumcision, three foreskins (40/.) were found to contain HPV DNA, with no correlation to the abnormal PAP smears of the mothers (Roman and Fife, 1986). HPV DNA was not examined in the mothers. In a series of 52 neonatal foreskins and 46 neonatal cervical specimens obtained at necroscopy and analyzed for HPV DNA by means of PCR and LI consensus primers, no evidence was found for HPV infection (Chen et 6il., 1993). Recent cervical cytology was available in 70 of the mothers, of whom only six had cytologic evidence of HPV infection Laryngeal papillomas are the most common benign tumors of the larynx in infants and children. There are two forms of laryngeal papilloma, one appearing at an early age (juvenile-onset papilloma; JOP) and the other in adults (adult-onset papilloma, AOP). Laryngeal papillomas are usually located on the vocal cords and epiglottis or subglottis but can involve the entire larynx as well as the tracheo-bronchial tree and even the lungs (Hirschfield and Steinberg, 1989; Kashima et al., 1993). The lesions may be single or multiple. Surgery is generally indicated in children more often than in adults, and malignant conversion also appears to be more common in JOP than in the AOP disease Figure 1. Oral Fpapilloma of a seven-year-old child. (Mounts and Shah, 1984) 1 1(2):2 59-274 (2000) Crit Rev Oral Biol Med Downloaded from cro.sagepub.com by guest on August 22, 2014 For personal use only. No other uses without permission. 261 TABLE 2 Reported Anogenital Warts in Children Aged Between Newborn and 12 Years Mode of Acquisition (N) C D E F G References A B 1967-1989*Boyd, 1990 1968-1980*Neinstein etal., 1984 Shelton etal., 1986 1986 RocketaL., 1986 1986 5 0 0 0 0 0 10 0 0 2 1 0 10 2 8 0 6 0 0 0 0 0 0 0 6 0 0 1 0 0 15 28 0 8 1 21 0 2 0 9 0 1 5 13 26 0 7 16 69 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 6 10 0 0 0 0 5 0 1 0 0 2 0 0 7 2 2 0 0 0 0 1 5 16 5 0 66 2 11 0 1 0 0 0 5 0 10 0 0 0 0 0 1 0 0 3 4 0 0 0 4 8 0 2 0 1 0 0 0 0 0 4 1 1 0 0 0 4 0 0 0 0 0 0 0 6 3 2 0 1 21 32 12 Year 1989 1989 Hanson eta!., 1989 Weitzner etaL., 1989 TOTAL (136) 1990 1990 1990 1990 1990 1991 1991 1992 1992 1992 1993 1993 1993 1993 1993 1994 1994 1995 TOTAL (339) Padel eta!., 1990 Obalek et aL., 1990 Cohen etaL., 1990 Gibson et aL., 1990 Kumar etal., 1990 Sundararaj etaL., 1991 Nuovo eta/., 1991 Igawa and Nakano, 1992 Derksen, 1992 Matsumura eta., 1992 Handleyetal., 1993b Yun and Joblin, 1993 Tamsen etaL., 1993 Handley et aL., 1993a Obalek eta!., 1993 McLachlin etal., 1994 Gutman etal., 1994 deVilliers, 1995 0 0 2 0 0 1 0 3 7 0 0 4 0 0 1 0 12 25 0 5 10 0 0 54 0 0 9 0 0 12 14 41 218 A = Sexually active; B = Suspected sexual abuse; C = Proven sexual abuse; D = Autoinoculation; E = Possible non-sexual transmission from other family members; F = Possible vertical transmission from the mother; G = Unknown source. Includes cases where no data from sources other than sexual abuse were recorded. * = Review. The specimens were obtained after birth, and some degree of autolysis was present in 30 samples, which might have adversely affected the detection of HPV DNA in these samples (Chen et al., 1993). (2.3.2) Condylomas Ano-genital warts in children may have serious medical, social, and legal implications. Issues such as the sexual abuse of the child, transmission of the virus from the mother to the child, as well as the potential for the future development of ano-genital malignancies in children with ano-genital HPV infections, especially with HPV 262 types 16 and 18, cause a great deal of anxiety in parents. Ano-genital warts in girls affect vulvar, vaginal, urethral, and peri-anal areas. Most lesions in boys are located in the peri-anal area. Penile warts are rare, although they have been described (Copulsky et al., 1975; Kumar et al., 1990; Oriel, 1992). The vast majority of ano-genital HPV lesions in children are condylomatous or papular (Fig. 2). Flat warts, after application of 5% acetic acid, have also been described, usually in the presence of condylomatous and papular lesions (Cohen et al., 1990; Oriel, 1992). In the 1990s, the reported incidence of ano-genital warts has dramatically increased in children. Until 1990, only 136 cases had been reported, whereas between 1990 and 1994, at least 326 additional cases were described (Table 2). This trend is considered to parallel the increased incidence of anogenital warts in adults (Bennett and Powell, 1987; Koutsky et al., 1988). (2.3.3) HPV types detected In anogenital warts of children In all the studies presented in Table 2, 254 of 457 ano-genital warts in children were analyzed for HPV DNA. HPV DNA was found in 230 (90.5%) of those 254 samples, and the type distribution was: HPV 6 and 11 in 75.6%, HPV 2 in 11.3%, HPV 16/18 in 5.6%, and HPV 27 or 57 in 3% of the positive samples. Detection of the genital types HPV 6, 11, 16, and 18 was suggested to imply either a sexual or a vertical transmission, and the presence of cutaneous type HPV 2 hetero- or auto-inocu- lation (Obalek et al., 1990; Nuovo et al., 1991). Figs. 2 and 3 show a HPV type- 1-positive peri-anal condyloma of a two-year-old boy. No evidence of sexual abuse was found. Recently, Handley et al. (1997) studied ano-genital warts of 31 pre-pubertal children for the presence of HPV DNA. In these warts, HPV 2 was the most common type of HPV detected (1 3/3 1), followed by HPV 6 (7/3 1), HPV I 1 (5/3 1), and HPV 16 (1/31). The results suggest that the mucosal HPV type in a child's ano-genital warts signifies transmission from mucosal warts, and, conversely, that cutaneous HPV 2 signifies transmission from warts at a cutaneous site. The authors also concluded that the high prevalence of HPV 2 in children's warts and the low prevalence of sexual abuse (two of 31 children) suggest that innocent auto- or hetero-inoculation from cutaneous warts may be a common way for children to Med Bid Med Oral Biol Rev Oral Crit Rev Crit Downloaded from cro.sagepub.com by guest on August 22, 2014 For personal use only. No other uses without permission. 11(2):259-274 (2000) gous with other DNA viruses where genes are turned on according to a specific time schedule in the course of productive infection, The so-called early genes are expressed shortly after infection prior to the onset of DNA replication. Early gene products are also involved in transformation of the host cells. The late genes code for structural proteins of viral particles and are activated during the final stages of the viral cycle. In HPVs, there are eight ORFs: six early genes, referred to as El, E2, E4, E5, E6, and E7; and two late genes, LI and L2 3A, lenison et al. ( 1990) were the first to study serum IgG antibodies to HPV 6b, 16 and 18 E and L gene products Figure 2. A peri-anal condyloma of a two-year-old child before (A) and after treatment (B) in hospitalized children (n = 81, age > with local alpha-interferon compression (courtesy of Dr. Olli Ruuskanen). 12 mos). Antibodies to L gene proacquire ano-genital warts, Auto- or hetero-inoculation teins were detected more frequently than those to the E can also explain the presence of mucosal types in chilproteins, Antibodies were detected in 57%'O of the children's ano-genital warts (Handley et al., 1997). dren, and antibody to LI protein of HPV 6b was the most frequent (Ienison et al., 1990). Bonnez et cil. ( 1992) (3) Detection of Serum Antibodies to HPV analyzed sera from 32 children with a biopsy-confirmed HPV serology offers another potential means for assesslaryngeal papillomatosis and 31 healthy children for ment of the prevalence of HPV infection in children. antibodies to HPV 6b and HPV II LI fusion proteins. In Currently, the main obstacles of HPV serology are the pluthe diseased group, 47%O (15/32) proved to be seroposirality of HPV types and weak immunogenicity of HPVs. tive, but 10% of the controls also harbored these antiHowever, interest in serological detection of HPV has subbodies The difference was statistically significant, howstantially increased in the past few years. This does not yet ever (P = 0.001). lochmus-Kudielka et ali (1989) examapply to children, however, because only six studies are ined patients with and without HPV infection for the available in which serum HPV antibodies have been analyzed in children (lochmus-Kudielka et ci., 1989, lenison et al., 1990, Bonnez et ci, 1992; Cason et ail., 'tv 1992, 1995, MOller et al., 1995) The data seem to be unanimous in that HPV seropositivity is remarkably more com\ mon in children and adolescents than in adults. Importantly, these studies clearly e indicate that seroreactivity to HPV 6 and M ,9 HPV 16 infections seems to be common and develops early in life. The available data are reviewed below. For those readers who are not familiar with HPV, a short overview on viral genome will be presented, The size of the genome of human papillomavirus is about 7.9 kb. All putative protein coding sequences (open read- Figure 3. HPV 11 DNA was detected in the biopsy sample taken from the lesion ing frames, ORFs) are restricted to one shown in Fig. 2. Fype The positive signals with in situ hybridization were found in the upper DNA strand, The individual frames are part of the epithielium in two different regions. The strong signals indicate a productive classified as early (E) or late (L), analo- HPV infection. i. - ' I2nnnI 74 (2000) 111121 59-2274 1(2):225Q cr11 R.'e (Thrcl Crit Rev Orcit Biol Med Binl M'd Downloaded from cro.sagepub.com by guest on August 22, 2014 For personal use only. No other uses without permission. 263 263 tivity in younger age groups was seen Serum antibodies (IgG) to different HPV 16 gene products were measured. Low positivity rates were found for E6 (5 l'o(, E7 (2.5%), or LI -L2 proteins (1.5%), but 20.3/,, of the sera reacted with the E4-specific peptide Interestingly, no correlation was found to occur between seropositivity and the detection of HPV DNA (Mund Yt al., 1997) To conclude, all these studies indicate that HPV type 6 and/or 16 infections are common at an early age and may provoke a serological response. However, the importance of these HPV antibodies acquired during childhood is not understood Do they neutralize the virus or do they help the virus escape the immunological defense system? These are some of the key questions for the future studies in this field of HPV research Figure 4. A plantar wart of a six-year-old boy. The wart was HPV 1 -DNA -positive, as detected by in situ hybridization. presence of HPV antibodies to HPV 16 E4 and E7 Antibodies to E4 and E7 were detected in 18% and 3 7% of the 336 control subjects, respectively. The age range of the control group was from 3 months to 90 years. The highest detection rate (40.7%) of E4 antibody positivity was found in the II -to-20-year age group. Muller et al. ( 1995) reported HPV 16 E4 antibodies in 1.14% of their adult population, but the prevalence was much higher (20%) in children and adolescents. In another recent study, investigators used HPV 16 LI and L2 proteins to examine sera from 229 children to determine the age at which IgM antibodies to HPV were acquired (Cason et al., 1995). A bimodal distribution of IgM seropositivity was found peaking between 2 and 5 as well as between 13 and 16 years of age, suggesting that two distinct modes of transmission may occur (Cason et a)., 1995). Marais et al. (1997) tested sera from 155 children (aged between I and 12 years) by an enzyme-linked immunosorbent assay (ELISA) for serum IgG antibodies to 3 HPV peptides (HPV-16 E2 1E2-161, HPV-18 E2 )E2-181, HPV-16 LI ILI-16)), as well as HPV 16 virus-like particles (VLP-16) and BPV type I virus-like particles (BPV-VLPs). Antibodies were detected to E2-16 (44.5%), E2-18 (18.7%), LI-16 (20%), VLP-16 (4.5%), and BPV-VLP (5.1%). Between the ages of 3 and 12 years, the prevalence of antibodies to E2- 16 decreased with age. Only one report has been published where an attempt was made to correlate the detection of HPV DNA in buccal or genital swabs of children with HPV antibody response (Mund et al, 1997). Samples obtained from 79 children were tested, and low-level positivity was found in 34 samples, twice as often in oral swabs than in genital swabs. No sexspecific difference was found. A trend toward higher posi- 264 (4) Modes of HPV Transmission HPVs are transmitted directly by skin or mucosal contacts, or indirectly through contaminated objects, or sexually or perinatally. Table I summarizes the modes of HPV transmission in children. According to the best available estimates, the incubation period for condyloma acuminata varies from three weeks to eight months and that of skin warts from two weeks to more than a year (Bunney et cik 1987). (4.1) NON-SEXUAL TRANSMISSION Infections with HPV types causing skin warts are usually acquired through micro-injuries. Transmission occurs either directly from one person to another, or indirectly via contaminated objects or surfaces. In children, indirect HPV transmission to fingers and hands from shared glue pots has been reported (Bunney ct Il., 1987). Auto-inoculation (by scratching) from one site of the body to another is also possible HPV 2 is frequently detected in lesions of the oral mucosa, and it might be acquired by the chewing of common warts present on hands. The increased incidence of cutaneous warts in children more than 5 years of age is believed to be due to exposure to common showers during the first years of school (Schiffman, 1994, lohnson, 1995). Fig. 4 shows a typical plantar wart of a child. The lesion was HPV type-1-positive. We were interested in determining whether HPV DNA can be detected in the floor and seat surfaces of humid dwellings-e .g, showers, saunas, and dressing rooms. The survey included three bathing resorts, one indoor swimming pool, two schools, and two private homes. The samples were collected with a toothbrush. Beta-globin (human single-cell gene) could be amplified only from one of the 36 samples collected. No HPV DNA- Crit Rev Orai Biol Med11 ](2):259-274 (2000. Downloaded from cro.sagepub.com by guest on August 22, 2014 For personal use only. No other uses without permission. positive sample was found. Our results indicate that transmission of genital HPV infection via floor or seat surfaces on the above premises is highly unlikely (Puranen et al., 1996b). (4.2) SEXUAL ABUSE TABLE 3 Maternal Genital Condylomata as a Source of HPV-induced Lesion in the Child Time of Maternal HPV Infection and HPV Type Birth Reference Age at Onset, Location Hajek, 1956 In contrast to the unequivocal Pregnancy, delivery No data 3 mos, laryngeal Patel and Groff, 1972 Pregnancy, delivery No data 13 mos, vulva data on sexual transmission of Cook et 1973 al., Delivery No data 1 mo, laryngeal genital warts in adults and sexuDelivery No data 6 mos, laryngeal ally active adolescents, reports Delivery data No 4 mos, laryngeal (3 children) on the primary mode of transmiset al., 1978 Eftaiha Pregnancy, delivery No data 3 mos, peri-anal sion of genital warts in children Tang et al., 1978 Pregnancy, delivery Vaginal 0 mo, peri-anal have been more contradictory De Jong et al., 1982 After pregnancy No data 14 mos, peri-anal (Gutman et al., 1992). In children, Pregnancy, delivery No data 7 mos, peri-anal the issue of genital warts origiZamora et al., 1983 Pregnancy No data 2 yrs 6 mos, genital nating from sexual abuse was Rogo and Nyansera, 1989 Pregnancy Section 0 mo, neck, ear raised in the 1980s, when vulvar Williams et al., 1990 Pregnancy No data 3 yrs 6 mos, gingiva Sundararaj et al., 1991 Pregnancy, delivery condylomata in young children, Vaginal 8 mos, peri-anal, laryngeal Igawa and Nakano, 1992 After delivery No data 3 yrs, perineal skin previously considered extremely Obalek et al., 1993 Pregnancy No data 1 wk, anal rare, were reported with increasPregnancy No data 2 yrs 8 mos, anal ing frequency (Stumpf, 1980). The Pregnancy No data 6 mos, anal full extent of the complex probPregnancy No data 10 yrs 9 mos, anal lems posed by genital warts in Pregnancy No data 6 yrs 11 mos, genital small children was fully appreciMenton et al., 1993 Pregnancy, delivery Vaginal 2 yrs, scrotum ated only in the early 1990s. Table (HPV6/11) (HPV6/11) 2 summarizes the studies on Handley et al., 1993b Unknown Vaginal ? 3 yrs, peri-anal anogenital warts in children aged (HPV6/11) (HPV6/11) between newborn and 12 years. Unknown Vaginal ? 2 yrs, clitoris Unknown Sexual abuse was proved in only Vaginal ? 10 mos, vulva Unknown Vaginal ? 2 yrs, peri-anal 32 of the 339 children with Handley et al., 1993a Pregnancy Vaginal 0-1 mo, anogenital anogenital warts. (5 children) Rose and Thompson (1989) Delivery Vaginal 1-3 yrs, anogenital (7 children) reported a series of 15 children Alberico et al., 1995 Unknown 10 Vaginal mos, laryngeal with ano-genital warts. Of these (HPV 6/16) (HPV 6) 15 children, 12 were referred for an assessment of sexual abuse, which could be confirmed in six cases, strongly suspectsuggested, including auto-inoculation. Nevertheless, sexed in one, and excluded in three. In two additional cases, ual abuse was suspected or evident in only half of the the source of infection remained unclear. Seven biopsy children, suggesting that other routes of transmission samples were positive for HPV 6 or 11, one for 6/11 and (e.g., perinatal) might be involved. The authors concluded 16/18. Two samples were positive for HPV 2, and further, that although the likely mode of transmission was inditwo hybridized with both HPV 18 and HPV 2. The authors cated, to a certain extent, by the type of HPV, it can be emphasized that the diagnosis of sexual abuse was made confirmed only in conjunction with all available clinical on the basis of history rather than by clinical examinaand social information (Padel et al., 1990). tion, and that only two children showed physical signs of Undoubtedly, the assessment of pediatric ano-genital sexual abuse (Rose and Thompson, 1989). HPV typing condyloma as a result of possible sexual abuse is one of the most difficult issues in the entire field of HPV epiplays an important role in the determination of whether the source of infection might be mucosal transmission or demiology. Recently, techniques for interviewing and evalauto-inoculation from the skin. Accordingly, of the 17 uating children for suspected sexual abuse have been defined. Such an evaluation should always include (1) biopsy samples reported by Padel et al. (1990), 10 were positive for HPV 6 or 11, while 6 contained skin types HPV behavioral indication of abuse, (2) medical examination 2 or 3. In the latter case, non-sexual transmission was to identify physical indications of abuse, (3) microbiolog11(2)259-274 11(2):259-274 (2000) (2000) Crit Rev Oral Bid Crit Rev Oral Biol Med Med Downloaded from cro.sagepub.com by guest on August 22, 2014 For personal use only. No other uses without permission. 265 265 ic assessment of other sexually transmitted diseases (STDs), and (4) age-adjusted interviews of the child and caretakers by skilled personnel (Gutman et al., 1992, 1994). The detailed discussion of these issues falls outside the scope of this review. The latest guidelines from the Center for Disease Control and Prevention (1998) for the treatment of sexually transmitted diseases include an expanded section on *STDs, including HPV among infants, children, and pregnant women, and the management of patients with genital warts. (4.3) MATERNAL TRANSMISSION As early as 1956, Hajek suspected transmission of a viral wart from a mother to her child at birth. Since then, several studies have been published that provide more insight into the maternal transmission of HPV. Table 3 summarizes the cases where maternal genital condylomata have been proven as a source of HPV-induced lesions in the child. Because of its major impact on our understanding of the basic pathobiology of HPV infections, current evidence on maternal transmission of HPV and factors predisposing to this mode of viral spread are discussed below. (4.3.1) Laryngeal papillomas In 1956, Hajek wrote: "Multiple laryngeal papillomata are found in small children and adolescents. They are not hereditary, but in 20% of cases they can be found at birth." Following this early notion, a large number of studies have reported a relationship between JOP and maternal genital condylomata (Cook et al., 1973; Strong et al., 1976; Quick et al., 1980; Hallden and Majmudar, 1986; Abramson et al., 1987). Recently, a case of laryngeal papilloma was reported in a one-year-old child delivered vaginally (Alberico et al., 1995). The papilloma of the child was positive for HPV 6, and the cervical smear from the area of the condyloma of the mother was positive for HPV 6 and 16, as determined by PCR and DNA sequencing. Interestingly, the mother had been previously treated for cervical intra-epithelial neoplasia (CIN), a finding that suggests a residual infection by oncogenic HPV 16. The incidence of JO-RRP was found to be 0.6/100,000 and prevalence 0.8/100,000 in a Danish population at risk (Bomholt, 1988; Lindeberg and Elbr0nd, 1990). The incidence of JO-RRP seems to be considerably higher in the US, up to 4.3/100,000 (Derkay, 1995). Assuming that 25% of child-bearing women have genital HPV infections, of which 2-5% are clinically overt, it has been estimated that the number of births at risk for HPV infections in USA is 72,000 to 180,000 (Shah et al., 1986). However, the prevalence of genital condylomata in women of child-bearing age far exceeds the reported number of new cases of JOP. Thus, the risk of a newborn 266 contracting a laryngeal lesion as a result of viral transmission from an HPV-infected mother must be relatively low-according to the best estimates, on the order of 1:80 to 1:1500 (Shah et al., 1986). Children infected at birth may develop laryngeal papillomatosis during the first 5 years of life. In some cases, papillomas may spread extensively and cause aphonia or severe respiratory obstruction. Kashima et al. (1992) evaluated the risk factors of JOP and AOP. Compared with juvenile controls, lOP patients were more often first-born, delivered vaginally, and born to a teenage mother. AOP patients reported more lifetime sexual partners and a higher frequency of oral sex than adult controls. A maternal history of genital condyloma at the time of delivery or during pregnancy among RRP patients has been reported to vary from 54% to 67% (Cook et al., 1973; Quick et al., 1980; Hallden and Majmudar, 1986). In a series of 109 JOP patients, only one child was delivered by Caesarean section (Shah et al., 1986). These patients are also at risk, albeit low, of a malignant transformation of the laryngeal lesions during adulthood. JOPs are nearly always associated with HPV type 6 or 11 infection. The necessity of a Caesarean section in mothers with genital HPV infection has been debated. Evidently, more information on risk factors linking maternal condyloma with lOP is needed before Caesarean section can be advocated as a means of eliminating or reducing the risk of JOP in the newborn (Derkay, 1995). Recently, Shah et al. (1998) reported a relationship between observed and expected number of JO-RRP cases as follows: Caesarean births, 4.6-fold less; first-order births, 1.6-fold greater; and maternal age < 20 years old, 2.6-fold greater. Based on these results, the authors stressed that the option of Caesarean delivery should be discussed with a mother who has condyloma at the time of delivery. (4.3.2) Oral mucosa Sedlacek et al. (1989) were the first to demonstrate HPV DNA in 11/23 (48%) nasopharyngeal aspirates of infants born by vaginal delivery to mothers with genital HPV infection. Amniotic fluid samples after rupture of the membranes were obtained from 13 patients, and two of them were positive for HPV DNA. Fredericks et al. (1993), using PCR, analyzed exfoliated cervical epithelial cells, from women 6 wks post partum, for HPV DNA, and the results were compared with those from buccal mucosal smears of their babies. Eleven mothers had genital HPV types in their cervical smears, and eight children of these mothers had an identical HPV genotype in their buccal mucosal samples. Nineteen mothers had no HPV DNA detected in their cervical smears. Only one child had a buccal mucosal sample positive for HPV DNA (p < 0.0001). The authors concluded that a contamination of Med Oral Blot Rev Oral Crit Rev Crit Biol Med Downloaded from cro.sagepub.com by guest on August 22, 2014 For personal use only. No other uses without permission. 1 l(2):259-274 11(2):259-274 (2000) a child's mouth with genital HPV from the mother's cervix appears to occur commonly at birth or during the perinatal period. Such acquired HPV DNA or infection may persist for at least 6 weeks (Fredericks et al., 1993). St. Louis et al. (1993) assessed the frequency of HPV in HIV-infected women and the detection rate of the viruses in their children. They collected cervico-vaginal lavage specimens from 80 mothers living in Kinshasa, Zaire (52 HIV-seropositive and 28 HIV-seronegative at the time of delivery), and oropharyngeal and perineal specimens from 81 of their three-year-old children (21 HIV-seropositive and 60 HIV-seronegative). Detection of HPV in the mothers was highly associated with HIVseropositivity; HPV DNA was detected in 20 HIVseropositive and one seronegative mother. Ten children were found to be HPV-DNA-positive. However, detection of HPV in children was not associated with the mothers' HPV or HIV status or with the child's HIV status. Thus, these results do not specifically support the hypothesis of a mother-to-child transmission of genital HPV types (St. Louis et al., 1993). We recently obtained similar data in a series of 98 children (0.3 to 11.6 years of age) born to mothers included in our prospective cohort of 530 women (Puranen et al., 1996b). Our evaluations included medical history, clinical examination of the oral cavity and hand warts, as well as cytological samples from the oral mucosa for HPV detection by PCR and subsequent Southern blot hybridization (SBH). Altogether, HPV was found in 31/98 (31.6%) oral scrapings. Nineteen of the positive samples become positive only when hybridized, indicating a low viral load. At delivery, five mothers had a genital HPV infection with the same virus type as that found in their children. In an additional 11 mothers, genital infection with the same HPV type as in the child was diagnosed a few months before or after delivery. One child had an oral papilloma where HPV 16 was detected, a type that was also found in her mother's genital mucosa (Puranen et al., 1996b). These results support the concept that an infected mother can transmit HPV to her child, and that this infection can persist for years. Alberico et al. (1996) assessed the prevalence of HPV infection in pregnant women and the prevalence of maternal-to-fetal transmission in a prospective longitudinal cohort of 11 months' duration. They collected endocervical biopsy samples from 170 pregnant women during the 1st and/or 2nd trimester of pregnancy and/or at the onset of labor, and oropharyngeal secretions from their neonates. Of these subjects, 23 mother-baby pairs provided all biopsy and other samples. HPV DNA was detected by PCR in at least one of the three samples collected during the various periods of pregnancy in 31.2% of the mothers and in 30.4% of those completing the whole sampling protocol. HPV DNA positivity in the (2000) 1 1(2)259-274 (2000) 11(2):259-274 oropharyngeal secretions from the neonates was 21.7%. The concordance of HPV DNA positivity between the mothers at the time of labor and their neonates was 57.1%. Analysis of these data indicates that the possibility of HPV DNA transmission from an infected mother to the child is high, particularly when the maternal PCR test is positive at the time of delivery, or in the presence of a high viral load (Alberico et al., 1996). Similar data were reported from another recent study (Tseng et al., 1998), where 301 pregnant women and their neonates, born by vaginal delivery (n = 160) or Caesarean delivery (n = 141), were assessed by PCR for the presence of HPV 16 and 18 DNA sequences in buccal and genital swabs. The overall frequency of HPV 16/18 infection among the pregnant women was 22.6% (68/301). At delivery, the frequency of HPV transmission from HPV 16/18-positive mothers to their newborn babies was 39.7% (27/68). A significantly higher rate of HPV 16/18 infection was found at birth in infants delivered vaginally compared with those delivered by Caesarean section (18/35 or 51.4% vs. 9/33 or 27.3%, p = 0.042). These findings suggest that neonates are at higher risk for exposure to HPV after vaginal delivery than after Caesarean delivery (Tseng et al., 1998). These high rates of vertical HPV transmission were not confirmed by Smith et al. (1995), who found only one of the 25 baby-mother pairs to be positive for the same HPV type. An additional baby was HPV-positive, but the mother appeared to be negative. The samples were collected during the third trimester and prior to delivery from the cervix of the mothers and one to three days after birth from the oral cavity of the babies. The transmission rate was low (4% or 8%) compared with those reported in the other studies, but the method used for HPV detection was also less sensitive than PCR. A similar detection rate was reported recently (Watts et al., 1998). HPV-positive oral scrapings were obtained from three of 80 infants born to women with cervical HPV DNA detected at 34 weeks' pregnancy and from five (8%) of 63 born to women without HPV DNA (Watts et al., 1998). No clinical manifestations were found in the newborn babies. The authors concluded that the upper 95% confidence interval for detection of perinatal transmission from a woman with evidence of genital HPV was only 2.8%. Recently, Favre et al. (1998) found HPV genotypes (HPV types 5, 8, and 24) associated with epidermodysplasia verruciformis (EV) in the amniotic fluid and placenta specimens and cervical scrapes of a mother suffering from EV-induced skin lesions. The child was born by Caesarean section, and the amniotic fluid specimen was taken prior to rupture of membranes. No viral sequences were detected in peripheral blood mononuclear cells collected two years and six months before Caesarean section, rendering a hematogenous transmission unlikely (Favre et al. 1998). Med Oral Bid Rev Oral Crit Rev Biol Med Crit Downloaded from cro.sagepub.com by guest on August 22, 2014 For personal use only. No other uses without permission. 267 267 (5) HPV in the Neonates-A Passenger or True Infection? weeks, HPV DNA persisted in 8/31 (26%) infants, HPV 16 in six, and HPV 18 in two infants. Currently, HPV infection can be diagnosed only by the detection of virus-induced epithelial changes or by the presence of HPV DNA/RNA in the tissue. HPV infection is regarded as a latent one, if there are no clinical or histological signs of HPV infection detectable but viral DNA is found with PCR. Repeated detection of HPV DNA in tissue and/or cell samples taken from the same anatomical region at different time points indicates that the virus has infected the tissue and is not detected on the basis of the contamination of the mucosal surfaces. So far, only a few studies have analyzed the persistence of viral DNA in newborn babies. Cason et al. (1995) reported persistent HPV DNA in 3 of 4 oral smears of babies who had HPV-DNA-positive nasopharyngeal aspirates at birth. The babies were born to mothers with HPV-DNApositive cervical swabs. The nasopharyngeal aspirate of one baby born to an HPV-DNA-negative mother was also positive. HPV DNA persisted for at least 6 weeks in 79.5% of the babies and for six months in 65%. Fredericks et al. (1993) sampled cervical cells from women 6 wks post partum and buccal smears of their babies for analysis of HPV DNA by PCR. In 73% (8/1 1) of the mother-baby pairs, an identical HPV type was detected in both the buccal mucosa of the newborn and the uterine cervix of the mother. This study also confirmed that HPV infection transmitted from the mother at birth can persist for at least 6 weeks. Cason et al. (1995) assessed whether HPV 16 and 18 DNA in infants contaminated at delivery persists until the infants are 6 months of age. Of the 61 pregnant women recruited, 42 (68.8%) were HPV 16- and 13 (21.3%) were HPV-18-DNA-positive. At 24 hrs following delivery, the transmission rates from HPV-DNA-positive mothers to their infants was 73% (HPV 16, 69%; HPV 18, 76.9%). Ten mothers who were HPV 16- and 18 DNA-positive delivered six (60%) infants who were also dual-positive at 24 hrs (Cason et al., 1995). HPV DNA persisted for up to 6 weeks in 79.5% (HPV16, 84%; HPV 18, 75%) of those infants who were positive at birth. At 6 months, persistent HPV 16 DNA was still detected in 83.3% of the infants, but HPV 18 DNA had dropped to 20% by this time. Similar data have been recently provided by other workers as well. Pakarian et al. (1994) used PCR and detected HPV DNA in the cervical swabs of pregnant women between the 20th and 38th weeks of pregnancy as well as in the buccal and genital swabs of their infants at 24 hrs and 6 wks after delivery. Twenty of the 31 (65%) women were positive for HPV DNA. A total of 12/32 (38%) infants were HPV-DNA-positive at 24 hrs. Five mother-infant pairs showed HPV 16, two had HPV 18, and three had an HPV 16 and 18 double-infection. At six The above results are fully consistent with our own results (Puranen et al., 1997). In a study on the potential oropharyngeal exposure of infants to cervical HPV infection in the mother, 106 infants born by vaginal delivery or Caesarean section and their 105 mothers were analyzed by PCR and subsequent confirmation with direct sequencing and single-strand confirmation polymorphism (SSCP). HPV DNA was detected in the cervical scrapings of the mother and nasopharyngeal aspirate fluid (NPAF) of her infant. Both the mother and her child were positive for the same HPV type in 29 mother-infant pairs. Interestingly, five infants born by Caesarean section were also HPV-DNA-positive for the same HPV type as their mothers. The concordance between the HPV types of the mothers and their newborns was 69% (29/42). Regardless of a perfect match in the HPV types between the mothers and their infants, the overall HPV DNA positivity in NPAF of infants was 37% (39/106 infants) (Puranen et al., 1997). The most frequent HPV type occurring in both infant and mother was HPV 16 (10 pairs), followed by HPV 33 (3 pairs). HPV 6, 11, 31, or 53 was found in two pairs and HPV 18 or LVX160L1 in one pair. Unknown types were found in eight pairs and multiple types in two pairs. Analysis of the follow-up data showed that vertically transmitted HPV DNA of the same type was detectable from 2 days up to 3 years in 16 of the 36 (44%) babies. In 15 cases, HPV DNA was no longer detectable at the age of 2-4 days. HPV DNA was detected in another five babies during follow-up, but the HPV type was different from that detected in NPAF samples 268 Crit Rev (Puranen et al., personal communication). Interestingly, baby born by Caesarean section had HPV 16 and 33 detectable in the NPAF sample at birth. Oral smear after 3 years was also HPV-positive. The HPV type detected in the mother of this baby at delivery was HPV 33. Analysis of these data clearly suggests that great individual variation occurs in babies in the persistence of neonatally acquired oral HPV infections (Puranen et al., 1997). In addition to our study, there is only one other study confirming the maternal origin of infant infections by determination of the nucleotide sequence of HPV. By sequencing the amplified LI region, we found 12 identical samples in mothers and their newborn babies. The detected HPV types were HPV 6b, 11, 16, 33, 53, and a new type, LVX16OL1. Another 14 mother-baby pairs exhibited identical HPV types, as shown by the similar patterns of SSCP. Kaye et al. (I1996) determined the nucleotide sequence of the upstream regulatory region (URR) of HPV 16 in cervical smears from 13 HPV-DNA-positive mothers and oral and genital swabs from their infants at 6 wks and 2 yrs of age. Concordant variants or prototypic sequences were detected in nine of 13 mother/infant sample pairs, indione Oral Bid Crit Rev Oral Biol Med Downloaded from cro.sagepub.com by guest on August 22, 2014 For personal use only. No other uses without permission. 1 1(2):259-274 (2000) cating that up to 69.2% of HPV-16-positive infants acquired the virus from their mothers. (5.1) VIRAL LOAD AND VERTICAL TRANSMISSION So far, only two studies have evaluated the impact of the viral load as a determinant of HPV transmission. Kaye et al. (1994) analyzed the viral load in cervical/vaginal cells of 15 pregnant HPV-16-infected women. Eight of these women had infants who were positive for HPV 16 DNA at genital and/or buccal sites. The viral load was estimated by laser densitometry of the PCR products. The eight mothers (four with a history of abnormal smears and two with previous genital warts) who transmitted the infection to their infants had significantly higher viral loads (p < 0.05) than those who did not. The authors concluded that the viral load is an important although not the sole determinant of the transmission of HPV 16 from the mother to her infant (Kaye et al., 1994). Thus, other factors such as immunological status and genetic constitution may contribute to the transmission and subsequent persistence of the virus. Similarly, Alberico et al. (1996) undertook a study of 23 mother-baby pairs and concluded that the frequency of transmission of HPV from an infected mother to the fetus is high in the presence of high viral load. (5.2) Is THE TRANSMISSION OF HPV in utero POSSIBLE? Theoretically, in utero transmission of HPV can occur hematogenously, by semen at fertilization, or as an ascendant infection of the mother. It is known that HBV, CMV, HSV, parvo, and rubella virus infections can be transmitted from the mother to the child in utero (Mounts and Shah, 1984; Matero and Sever, 1990; Whitley, 1993; Treadwell, 1994). So far, hematogenous HPV transmission has been considered unlikely, because HPV is known to multiply locally at the site of entry on the skin or mucous membranes, and there has been no proof of disseminated HPV viremia (Mounts and Shah, 1984). Nevertheless, there are reports on congenital condyloma lesions (Tang et al., 1978), even after Caesarean section, without premature rupture of the membranes (Rogo and Nyansera, 1989). More importantly, in these mothers, amniotic fluid also contained HPV DNA. Armbruster-Moraes et al. (1994) used PCR to analyze the amniotic fluids from 37 pregnant women with cervical HPV lesions. They found HPV DNA in 65% (24/37) samples: HPV 16 in 13, HPV 18 in 5, and 6 samples remained untyped. In contrast, a recent study could not find HPV DNA in amniotic fluid (Maxwell et al., 1998). However, these investigators used only visualization of amplified HPV DNA fragments on the gel, and DNA samples below 10 ng are not easily detectable (2000) 1 L(2):259-274 (2000) 11(2):259-274 by this technique. As described above, Favre et al. (1998) also found HPV DNAs in amniotic fluid and placenta specimens by a nested PCR method. Because the same HPV types were also detected in cervical smears of the mother, an ascending infection of the placenta was suggested. In the early 1990s, four studies were published providing evidence of HPV detection in blood cells. However, the results of these studies have never been confirmed by other groups. Tseng et al. (1992) assessed cervico-vaginal cells and peripheral blood mononuclear cells (PBMC) from 52 pregnant women in the third trimester of pregnancy as well as cord blood specimens from neonates born to these mothers (Tseng et al., 1992). HPV 16 DNA was found in 6 (11.5%) cervico-vaginal smears and in 9 (17.3%) samples of peripheral blood mononuclear cells. Seven cord blood specimens of neonates born to nine mothers with HPV 16 DNA in their PBMCs were found to contain HPV 16 DNA. One cervico-vaginal and two PBMC specimens contained HPV 18 DNA, but this type was not found in the cord blood specimens. HPV DNA has been detected in circulating blood leukocytes (Kedzia et al., 1992; Pao et al., 1991). HPV 16 DNA has been detected in granulocytes and on lymphocytic cell membranes in the blood of cervical cancer patients (Kedzia et al., 1992). Pao et al. found HPV DNA, of various types, in PBMCs of 13/24 (52%) patients with urogenital HPV infections, but in none of 19 individuals without urogenital HPV infections (Pao et al., 1991). Similarly, Jalal et al. (1992) found HPV 16 DNA in blood mononuclear cells of 2/8 (25%) individuals who had latent oral HPV 16 infection. In two of them, peripheral blood lymphocytes also exhibited positive amplification with HPV 16 primers (Jalal et al., 1992). Honig et al. (1995) studied HPV DNA with in situ hybridization (ISH) from leukocytes of 40 patients with HPV-positive oral squamous cell carcinomas. In 92.8% of these cases, HPV DNA of an identical type could be detected in leukocytes taken from pre-operative blood samples and oral carcinomas. Despite these reports, the true hematogenous transmission of HPV must still be regarded as an unconfirmed concept. Recently, HPV DNA has been found in hydatidiform moles and choriocarcinomas of the placenta (Pao et al., 1995). Importantly, in one study, HPV DNA was demonstrated in syncytiotrophoblasts of the placenta in 5/6 cases of spontaneous abortion by ISH PCR (Hermonat et al., 1997). It was speculated that, while trophoblastic cells maintain the placental contact with maternal tissues, it might well be that HPV-infected trophoblasts may have been a predisposing factor in the compromised pregnancy in these cases (Hermonat et al., 1998). These observations could also explain the transplacen- Biol Med Oral Biol Rev Oral Med Crit Rev Downloaded from cro.sagepub.com by guest on August 22, 2014 For personal use only. No other uses without permission. 269 269 tal transmission of HPV from an infected mother to the fetus. At the mo ment, our laboratory is currently attempting to assess the role of the placenta as the source of such persistent HPV infections. implications in the design of any vaccination programs against HPV infection aimed at eliminating its worst outcome: cancer of the uterine cervix. (6) Implications of Maternal HPV Transmission REFERENCES The current consensus is that, not infrequently, the newborn baby is exposed to the cervical HPV infection of the mother, although no reliable exposure rates can be calculated. In reported studies, HPV DNA detection rates in mother-baby pairs have ranged from 4% to 87%. Several obvious reasons for this variability can be listed: (1) The study groups have been small (11-98 children and mothers); (2) the modes of sample collection have varied; (3) the children have not been of the same age in the different studies; (4) different HPV DNA detection methods have been used; (5) technical aspects have to be kept in mind, including contamination of samples either in hospitals or in laboratories, and inappropriate sample collection; and (6) false-positive results in PCR amplification. Recent follow-up studies have confirmed, however, that maternally transmitted HPV can cause a true infection of the upper aerodigestive tract or genital region of the child, and that the virus is not just a passenger. Although HPV infection can probably be acquired during the baby's passage through an infected birth canal, transmission in utero or post-natal acquisition seems to be possible as well. Several studies (Cason et al., 1995; Puranen et al., 1997) have reported cases of HPVpositive newborn babies having HPV-negative mothers. This might be because HPV DNA was not detected in the genital tract of the mothers, i.e., a false-negative result, which does occur. The other possibility is that the virus resides in the placenta, a tissue which has not thus far been systematically examined. Further, the concordance of HPV types detected in the newborn babies and their mothers is only in the range of 57% to 69%. This might signify that the infants may have acquired HPV infection post-natally from a variety of sources, including breast milk, from siblings via kissing, or even through exposure to contaminated fomites, or that semen has been the vector of virus transmission. A proper understanding of viral transmission routes is of crucial importance, particularly because several vaccination programs are ongoing worldwide. The serological response to HPV detected in various populations of young women might be due to genital infection, but there is currently no way to rule out the possibility that the HPV infection may be acquired earlier through the oral mucosa. Theoretically, HPV infection already acquired in utero or post-natally may even induce immunological tolerance to HPV infection. It should be evident that these considerations would have important Abramson AL, Steinberg BM, Winkler B (1987). Laryngeal papillomatosis: clinical, histopathologic and molecular studies. 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