Background
Human papillomavirus (HPV) is a known oncovirus and it has potential to cause carcinoma in the genital, anal and oropharyngeal regions [
1]. The natural history of HPV is currently well known in the female cervical region as well as in the oropharyngeal region. Nonetheless, HPV can infect other body sites as well [
2,
3].
Several studies have reported the presence of HPV DNA in 2–31% of semen samples from healthy men [
4‐
7]. Luttmer et al. [
8] found that the presence of HPV in semen was associated with the presence of HPV in the penile scrapes but not with flat penile lesions (FPL). Foresta et al. [
9] found HPV16 proteins in peripheral blood leukocytes in individuals with HPV-positive seminal samples. Therefore, suggesting the presence of HPV in semen seems not to be only local. HPV in semen has been implicated in male infertility. A systematic review including 21 original articles, concluded that HPV DNA found in semen is connected with reduced semen quality [
10]. In a relatively recent study, women undergoing intrauterine insemination with HPV-positive semen were found to have four times fewer pregnancies than couples with HPV-negative semen [
11]. To date, the association between the bacterial microbiota and HPV DNA in semen has yet remained unknown. Besides various factors, including sexual behavioural characteristics being determinant of the presence of HPV in semen particularly in adjusted analysis [
8], other factors such as the semen microbiota could potentially impact the HPV status in semen. This speculation seems logical following the reports on concordance of HPV detection in semen and penile scrapes [
8] and potential role of penile microbiota (specifically bacterial communities) on penile HPV infection [
12]. Nonetheless, our knowledge about the interactions between HPV infection and the bacterial microbiota and its impact on human health is still limited.
Although limited, published literature in the last decade have given us a glimpse into the composition of semen microbiota. The semen microbiota is mainly composed of the genera
Lactobacillus,
Pseudomonas,
Prevotella,
Gardenella,
Corynebacterium, Staphylococcus and
Streptococcus [
13‐
17]. Semen microbial composition has been associated with seminal health [
13,
14,
16]. HIV infection, prostatitis (inflammation of the prostate gland) and sexual intercourse can all elicit an impact to the microbial composition in semen [
12,
15,
16,
18]. According to previous studies, changes in the relative amount of different bacteria have been linked with semen quality [
13,
14]. However, not all studies have been able to observe differences in semen bacterial microbiota between fertile and infertile couples [
14,
17]. This could be explained by differences in study design, study populations or methods.
Since it is known that seminal microbiota can influence fertility and even offspring health, it is important to understand aspects that might affect semen microbiota composition [
19]. We investigated the prevalence in HPV positivity in a subset of samples from Finnish Family HPV Study and evaluated the association between HPV and bacterial microbiota in these semen samples.
Discussion
In the present study, we detected that the presence of HPV in semen is associated with some detectable changes in the semen bacterial microbiota composition in healthy individuals. The bacterial microbiota of the semen samples consisted mainly of
Comamonadaceae,
Bifidobacteriaceae, Tissirellaceae, Corynebacteriaceae,
Delftia, unclassified
Comamonadeceae,
Propionibacterium and
Streptococcus members. The overall seminal bacterial composition has been seen to vary between different studies [
13,
14]. Previous studies have reported that the genera
Lactobacillus,
Corynebacterium,
Streptococcus,
Pseudomonas,
Prevotella and
Gardenella mainly constitute the healthy/normal semen bacterial microbiota [
13,
14,
17]
. The bacterial composition in our semen samples were detected to be somewhat different compared to previous studies, but overall, the genera
Corynebacterium and
Streptococcus were consistent. The small sample size may have an effect on our results.
The semen microbiota can be influenced by the bacteria colonized the penis, urethra and from the urine [
12,
19,
26‐
30]. Contamination from skin bacteria from the participants’ hands is also possible. The circumcision status of the men is seen to change the penile microbiota composition as well [
26,
28]. The Finnish Family HPV Study did not collect information about the male circumcision status, but in Finland it is not customary.
In the HPV-negative samples we detected higher abundance of Fusobacteria when compared to HPV-positive semen. Fusobacteria is a known oral pathogen [
31] which has not, to authors’ best knowledge, been detected in human semen samples before. In the female reproductive health, on the other hand, Fusobacteria have been detected to play a part in cervicovaginal dysbiosis and HPV persistence [
32].
Given that semen HPV and microbiota has been implicated in seminal health and disease/disorders, including infertility [
10,
11,
13,
19,
33] and that the impact of HPV infection on semen microbiota remains unknown, we characterized the semen microbiota in presumably fertile men with and without HPV infection. All men in our study were presumably fertile, since they were recruited in the Finnish Family HPV Study as fathers-to-be. In our study cohort, the prevalence of HPV positivity in semen samples was 19.4%. This was within the range (2 to 31%) that has been reported in previous studies [
4‐
6,
34,
35]. The prevalence of HPV has been reported to be slightly higher among men affected by unexplained infertility [
5,
10,
36]. Furthermore, HPV infection has been associated with negative changes in semen quality including impairment of sperm motility and presence of anti-sperm antibodies [
5,
37]. However, in our study, semen analysis (including sperm count test) was not performed to ascertain male fertility.
In our study, we detected HPV-positive semen samples to be more abundant with
Streptococcaceae, Peptostreptococcaceae,
Veillonellaceae, in addition with
Streptococcus, Serratia, Dialister and Peptostreptococcus (Supplementary Table
1). In line with our findings, present HR-HPV (high-risk HPV) infection has been connected with e.g.
Prevotella and
Dialister in one recent study [
12]. Furthermore, asymptomatic STI (sexually transmitted infections) have been shown to be more frequent in male with specific bacterial urine microbiota (mainly with
Prevotella and
Veillonella) [
29].
Previous studies have connected
Lactobacillus, Streptococcus, Veillonella and
Peptostreptococcus with undefined male infertility [
38,
39]. While HPV DNA found in semen has been linked to reduced semen quality
, the abundances of
Lactobacillus and
Streptococcus have been identified to be significantly higher in semen samples from healthy men [
13,
14]. In contrast to the present study, HPV DNA positive semen samples were associated with an increase of e.g.
Streptococcus and
Peptostreptococcus genera as compared to HPV DNA negative semen. Among the bacterial microbiota found in semen,
Ureaplasma has been described as a known pathogen connected strongly with male infertility [
40]. Both HPV infection and certain bacterial species, such as
Anaerococcus in semen have been associated in inferior semen quality in previous studies [
5,
10,
14,
36]. Male infertility is a complex multifactorial issue and cannot be explained by a single factor, such as HPV or presence of certain bacterial species. Furthermore, the connection between semen bacterial microbiota composition to male infertility is anything but simple [
17]. Nevertheless, it is therefore important to understand how HPV and bacterial microbiota interact and what impact this interaction might have on male reproductive health.
Previously, it has been shown that present viral infection with HIV can shape the bacterial microbiota composition and that the altered bacterial composition might enable viral transmission in addition with changes in the pro-inflammatory cytokines [
15]. It could be speculated that HPV might be able to interact with the bacterial microbiota in similar manner [
33].
This study has some limitations. Our study design restricts us from making definitive conclusions about the viral-bacterial associations. Furthermore, the relatively low number of samples in general and the low number of HPV-positive semen samples may have an impact on the results, as we did not find significant impact of seminal HPV on the diversity of semen microbiota. HPV DNA may also originate from the proximal excurrent ducts (including efferent ductules, the vas epididymis and the proximal vas deferens) and not from HPV-infected seminal cells [
8,
41]. The small number of samples is a limitation of the study and does not allow generalized conclusions Furthermore, the time of abstinence is based only on the participant’s own reports and might affect the sample quality and bacterial composition [
18]. In addition, only the cellular fraction of the semen was used for DNA extraction and we cannot completely rule out that there could not be small traces of bacteria present in the seminal plasma. Nevertheless, this is the first study to show that seminal HPV infection is associated with high relative abundances of specific bacteria in the semen microbiota of presumably healthy men.
Acknowledgements
The authors wish to thank all the past and present members of the Finnish Family HPV Study, especially the families participating in this study. From the original Finnish Family Human Papillomavirus Study Group, the authors wish to especially thank Seija Grénman, Hanna-Mari Koskimaa, Karolina Louvanto, Anna Paaso, Marjut Rintala and Marja Sarkola. We also want to thank Ms. Tatjana Peskova for her skillful help in the HPV MediCity Laboratory.
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