Review of 373 studies: “Among the 22 viruses for which we found evidence for detection in the semen following acute infection, nine had published evidence for sexual transmission as well.”

@RTHM_Health:

New research shows SARS-CoV-2 infection particles can persist in semen for up to 8 months after infection, raising critical questions about viral reservoirs and potential sexual transmission. The virus remained detectable in over half the study participants and was confirmed as infectious through cell culture. While decreased sperm quality showed signs of recovery by 6 months, the implications of viral persistence in the male genital tract remain under investigation.

This study adds to growing evidence that the male reproductive system may serve as an immune privileged site for virus reservoirs, similar to findings in Post-Ebola Syndrome.

@loscharlos:

Large review study on the subject:

“Evidence was found of detection of 22 viruses in human semen following acute infection.. nine had published evidence for sexual transmission.”

Covid, Zika, Ebola, Mpox, West Nile, etc. included. #LongCovid

Duration of viral persistence in human semen after acute viral infection: a systematic review Caitlin Pley, Laura Jung, Nadra Nurdin, Tim Venkatesan, Vasanth V Naidu, Rosemary James et al, May 2025, Volume 6, Issue 5 The Lancet

Summary

The persistence of viruses in human semen following acute infection can contribute to the ongoing transmission of a disease or cause resurgence after an outbreak has been declared ended. Viral persistence in semen affects embryonic development and male fertility, and the development of drugs and vaccines. We conducted a systematic review of viral persistence in semen in accordance with PRISMA guidelines. 373 original studies were included in this Review after screening 29 739 articles from five databases. Evidence was found of detection of 22 viruses in human semen following acute infection, including pathogens with pandemic potential. In addition to collating the largest evidence base to date on viral detection in semen following acute infection, this Review reports the maximal and median viral persistence (in days) after the onset of illness and evidence for sexual transmission and viability of the viruses in semen. Finally, the Review presents research gaps that need to be prioritised to guide further study of the dynamics of viral persistence in semen.

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Results

24 258 studies were screened in stage 1 of title and abstract screening, and 643 of them were retained for full-text screening. From the results of stage 1 review, a list of 27 viruses that cause acute infection in humans with published evidence for presence in semen or the male reproductive tract was compiled.

Stage 2 review, which involved a search for publications on detection of the viruses listed in stage 1 in semen or evidence for sexual transmission, yielded an additional 5481 studies, from which 325 studies were retained for full-text screening. Review articles were retained for reference screening, which led to the identification of an additional 61 articles for full-text screening. 677 full-text research articles were screened, and 373 articles were ultimately included in the systematic review. Figure 1 presents the PRISMA flowchart of the results of our literature search and screening. Detailed summaries of all the studies included in the systematic review, categorised as studies providing evidence for virus detection in semen (appendix pp 3–10), virus detection in other parts of the male reproductive tract (appendix p 11), and sexual transmission (appendix pp 12–16) are given in the appendix. …

Most studies included in the systematic review were case reports (98 of 373) or case series (120 of 373; appendix p 2). For most of the viruses, studies with various study designs were identified. A 2017 review on virus detection in semen found that only two viruses that cause acute infection had been systematically investigated for detection in semen: Zika virus and Ebola virus.¹⁰ However, the present systematic review identified several new and additional studies that have systematically investigated the presence of viruses in semen. Since we imposed no date restrictions, studies published between 1962 and 2023 were included in this Review.

22 viruses (belonging to 14 virus families) that could be detected in semen during or following acute infection in humans were identified (table). An additional three viruses for which there was evidence for detection in other parts of the human male reproductive tract, but not in semen, were also identified, as follows: Crimean–Congo haemorrhagic fever virus, hantavirus causing haemorrhagic fever with renal syndrome, and Heartland virus (figure 2). Two more viruses, hepatitis A virus and vaccinia virus, had evidence for sexual transmission but no evidence for detection in the semen or elsewhere in the male reproductive tract (figure 2).

Figure 2Evidence for detection of all 27 viruses in the semen, their viability in the semen, sexual transmission, and detection in other parts of the male reproductive tract

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Overall, 208 studies, encompassing 8387 participants, provided evidence on detection of viruses in semen during or following acute infection (table). The viruses were detected using a range of methods, including PCR, whole-genome sequencing, antigen detection using immunofluorescence and immunohistochemistry, and replication in cell and animal systems.

An overall proportion of carriage in semen among men infected with a specific viral pathogen could not be estimated owing to the high number of case reports and case series and owing to some prospective cohort studies having detection in the semen as an initial inclusion criterion, thereby exposing such an estimate to a high risk of bias.

However, the cross-sectional studies included in this Review suggested that the persistence of virus in semen following acute infection differs between pathogens. In larger studies (n>20) that systematically included and tested all men following defervescence of confirmed infection, virus was detected in the semen in 5–73% of the individuals following Ebola virus disease,^16–27 in 75% following Lassa fever,²⁸ in 33–100% following Zika virus infection,^29–33 in 46% following mpox,³⁴ and in 0–16% following COVID-19;^35–52 the interpretation varies with differences in timing of testing after acute infection.

The viruses with evidence for replication competency in the semen were adenovirus, adeno-associated virus, Chapare virus, dengue virus, Ebola virus, hepatitis E virus, Lassa virus, Marburg virus, monkeypox virus, mumps virus, Toscana virus, and Zika virus.

Among the 22 viruses for which we found evidence for detection in the semen following acute infection, nine had published evidence for sexual transmission as well.

Only epidemiological evidence for sexual transmission was available for adenovirus, Andes orthohantavirus, hepatitis E virus, Marburg virus, monkeypox virus, and West Nile virus. For dengue virus, Ebola virus, and Zika virus, we identified both molecular and epidemiological evidence for sexual transmission. We also identified three viruses (Crimean–Congo haemorrhagic fever virus, hepatitis A virus, and vaccinia virus) with evidence for sexual transmission but no evidence for detection in semen (figure 2).

The virus with the longest maximum detection time was Ebola virus (Zaire species), which was detected 988 days after discharge from an Ebola treatment unit and 965 days after onset of illness, in separate studies.⁵³^,⁵⁴ Since studies on viral kinetics following Ebola virus disease and Lassa fever either used days after onset of illness or days after discharge from Ebola treatment unit or hospital as their units of measurement, we chose to report these as originally recorded. In cases with sufficient individual-level data available for analysis, the median persistence was considerably shorter than the overall maximum detection time among all individuals (table). For example, the overall maximum detection of Zika virus in the semen was 941 days after onset of illness, yet the median persistence was only 57 days after onset of illness.

We found considerable variability between individuals with regard to the duration of persistence of virus in the semen, alongside substantial uncertainty in the duration of persistence in each individual. Many studies did not continue follow-up with individuals until they tested negative, or individuals were lost to follow-up, which suggests that the actual point of clearance of the virus from the individuals’ semen remained uncertain. For cases in which testing did continue until the individual tested negative, a period of uncertainty existed between the last positive and first negative tests. Finally, individuals who only ever tested negative could have tested positive at an earlier time after onset of illness. This inter-individual variability and intra-individual uncertainty is shown in figure 3.

A secondary outcome of this study was the immune status of the individuals, to identify an association between immunosuppression and the duration of persistence of virus in semen following acute infection. In most studies, immune status was not recorded, and thus, no trend could be discerned for most of the viruses presented in this Review. Of note, the overall maximum detection time of 941 days observed for Zika virus was in a patient who was immunosuppressed due to methotrexate, hydroxychloroquine, and steroid therapy.⁵⁵ The second longest detection of Zika virus was 414 days after onset of illness, in a patient with an unrecorded immune status.⁵⁶ Furthermore, the only report of detection of Rift Valley fever virus in semen is a case report of a patient with immunosuppression and a past history of kidney transplantation.⁵⁷

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Discussion

This Review identified 22 viruses causing acute infection that have been shown to persist in human semen, as compared with the nine viruses causing acute infections identified in the last broad review published on this topic.¹⁰ This Review also identified many newer studies using cross-sectional and cohort designs. The viruses identified in this Review were mostly vector-borne or transmitted through bodily fluids, the notable exception being SARS-CoV-2, which is, however, known to cause viraemia.⁵⁸ Nine of the 22 acute viruses identified had evidence for sexual transmission.

This Review only focused on viruses that cause acute infection, given the clinical and public health implications of persistence even after resolution of illness. Viral presence in the semen in the context of chronic infections, reviewed elsewhere,¹⁰^,¹¹ has been confirmed for HIV, hepatitis B, hepatitis C, cytomegalovirus, Epstein–Barr virus, human simplex virus 1, human simplex virus 2, varicella zoster virus, transfusion-transmitted virus, GB virus C, BK virus, JC virus, simian virus 40, simian foamy virus, human T-cell lymphoma virus 1, human herpes virus 6, human herpes virus 7, and human herpes virus 8.

The maximal detection times in semen varied between viruses, ranging from 8 days after onset of illness for Kyasanur Forest disease virus to 988 days after discharge from the Ebola treatment unit. Although the data might point to some association with viral families (for example, filoviruses and arenaviruses appear to persist longer than paramyxoviruses, poxviruses, and togaviruses), the maximal detection time is most likely also heavily influenced by the number of studies conducted and the number of subjects covered.

For example, the maximal detection times for flaviviruses were generally short, at 8 days for Kyasanur Forest disease virus, 21 days for yellow fever virus, 22 days for West Nile virus, and 37 days for dengue virus, whereas the maximal detection for Zika virus was 941 days in a man with immunosuppression and 414 days in a man presumed to be immunocompetent. Whether this difference has arisen because Zika virus has a functionally different pathophysiology with greater tropism to the male reproductive tract than other flaviviruses or because Zika virus has simply been studied more owing to its link to microcephaly remains unclear.⁵⁹

In addition to variation between different viruses, considerable person-to-person variability was also found. In cases with sufficient data, the median length of detection was often considerably shorter than the maximal detection time; this distinction is of central importance to public health recommendations and clinical guidelines (figure 3).

12 of the 22 viruses have also been shown to be capable of replication in cell culture or an animal system. Isolation of replication-competent virus from semen does not necessarily imply that the virus is capable of sexual transmission, as infection in this context will also be influenced by additional factors such as viral load, innate immune defences, and the capacity for viral entry into cells in the female and male reproductive tracts. Furthermore, viruses whose isolation was not attempted or was attempted but has been unsuccessful to date (eg, Rift Valley fever virus, chikungunya virus, and SARS-CoV-2), might still be capable of replication in semen and potential sexual transmission. Isolation of replication-competent virus is a difficult laboratory procedure; the failure rate of the assay plays a decisive role in whether viability can be shown, particularly for rare viruses with few semen samples.

Some studies reported interesting correlations between the length of detection and clinical parameters. Studies reported significant associations between length of detection of Ebola virus in semen and older age,¹⁶^,²⁶^,⁵⁴^,⁶⁰ severe disease,⁶⁰ uveitis,²² antibody titre against nucleoprotein,²⁷ and symptoms of eye or joint pain.¹⁶ Similarly, prolonged detection of Lassa virus RNA in the semen was associated with older age, higher viraemia at admission, more severe disease, and longer hospital stay.²⁸ The length of Zika virus detection was associated with the presence of conjunctivitis³² and markers of inflammation in the male reproductive tract, including elevated leukocyte counts and inflammatory cytokine concentrations in semen.²⁹

A major strength of this study is its highly sensitive search methodology, enabling inclusion of 373 studies for data extraction and identification of 22 viruses with persistence in semen following acute infection, a number much greater than the nine viruses found in previous reviews on this topic.⁷^,^10–14 Individual-level data were also extracted wherever available, allowing reporting on the longest maximum detection time in an individual and calculation of the median of maximal detection times, a figure highly relevant for clinical and public health decision making.

However, this Review also has its limitations, principally because of the studies published in this research area. The first limitation is a high likelihood of publication bias affecting the completeness of the results. Since the majority of the data were published in the form of case reports, a high possibility exists that case reports were either not written or not published when the individuals tested negative for viruses in semen. Despite this limitation, case reports are often best placed to provide epidemiological evidence for sexual transmission at a given timepoint. Although case reports offer evidence for several viruses for which studies with more robust designs have not yet been conducted and could stimulate further study, they do not permit estimation of the proportion of individuals who shed virus in semen following acute infection. Moreover, a large number of studies conducted and published on a particular virus can also be associated with a high likelihood of detecting outliers with long (or short) persistence.

We extracted the immune statuses of individuals, whenever reported, to discern a possible association with detection time, which enabled us to identify that the maximum individual detection time we extracted for Zika virus was in a man with immunosuppression, which was over 500 days greater than the next longest detection in a presumed immunocompetent man. However, we did not extract other variables for individual patients, such as age, symptoms, or laboratory parameters, as our pilot study found that these data were rarely reported.

The studies included in this Review are heterogeneous not just in terms of study design but also in the type of individuals included. Although most studies only included individuals with symptomatic disease, some studies were conducted in asymptomatic individuals, such as a few of the studies on COVID-19,³⁶^,⁴⁵^,⁶¹ and some studies tested semen samples from fertility clinics^62–64 or sperm banks.⁴¹^,⁶⁵ This heterogeneity also precludes unbiased estimation of the proportion of individuals with viral persistence in semen following acute infection, which is why we did not report this measure.

Heterogeneity in the sensitivity of assays used to detect different viruses can also play an important role. Viruses that are commonly studied most likely have diagnostic tools, namely methods to detect genetic material and replication competency, which are more sensitive and specific than those for viruses that are studied less frequently. This factor could play an important role in the differences observed between viruses.

A final limitation is the potential for bias arising because of the length of follow-up, and consequently, missing data, which could underestimate the maximal persistence of virus in semen reported in this Review. There are two main issues: first, not all studies continued testing in men who tested positive for virus in semen until they tested negative, either because the men were lost to follow-up or because testing was done in an ad hoc manner rather than a standardised one. As a result, the last positive test might be a substantial underestimate of the actual length of persistence. Second, individuals who tested negative in their first test or individuals who tested negative in one or two consecutive tests after initially testing positive were usually not followed up for the same length of time as individuals who continued to test positive. Given that viral kinetics in semen are known to fluctuate heavily, as has been shown most notably for Ebola virus,²⁰^,²²^,⁶⁶ such studies are most likely to stop follow-ups with some men who could later test positive again.

This Review identified several gaps in existing knowledge about the persistence of viruses in human semen following acute infection (table; panel), which could be used to guide future research. More epidemiological and molecular studies are needed to ascertain whether viruses that have been detected in human semen are capable of sexual transmission, and whether sexual transmission plays a relevant role in overall transmission. These studies are particularly important for the priority pathogens⁶⁸^,⁶⁹ Lassa virus, chikungunya virus, Nipah virus, and Rift Valley fever virus. Further studies are also needed to ascertain whether viruses detected in semen by PCR are viable, and to elucidate the kinetics of viral shedding in semen, including length of persistence, concentration, viability over time, and fluctuations.

Panel
Knowledge gaps around the persistence of viruses in human semen following acute infection

∗Sexual transmission of hepatitis A and E most likely occurs for a major part through direct or indirect oral–anal contact, yet a role for infectious semen cannot be excluded at present.67 Hepatitis E virus has been detected in human semen (table).

Viruses with evidence of presence in human semen but with no published evidence for sexual transmission

•Lassa virus
•Chikungunya virus
•Nipah virus
•Rift Valley fever virus
•Adeno-associated virus
•Chapare virus
•Enterovirus (including coxsackievirus A/B and echovirus)
•Kyasanur Forest disease virus
•Mumps virus
•SARS-CoV-2
•Severe fever with thrombocytopenia syndrome virus
•Toscana virus
•Yellow fever virus

Viruses with PCR detection in human semen but with no published evidence for viability

•Nipah virus
•Rift Valley fever virus
•SARS-CoV-2
•Chikungunya virus
•West Nile virus
•Yellow fever virus
•Severe fever with thrombocytopenia syndrome virus
•Andes orthohantavirus
•Enterovirus

Kyasanur Forest disease virus

Viruses with evidence of sexual transmission but with no studies on presence in human semen

•Crimean–Congo haemorrhagic fever virus
•Hepatitis A∗ virus
•Vaccinia virus
•Parvovirus B19

Viruses detected in the human male reproductive tract but with no studies on presence in semen

•Crimean–Congo haemorrhagic fever virus
•Influenza virus
•Rubella virus
•Vaccinia virus
•Severe acute respiratory syndrome virus
•Parvovirus B19
•Heartland virus
•Hantavirus causing haemorrhagic fever with renal syndrome
•Lymphocytic choriomeningitis virus
•Phlebotomus fever virus

Viruses with no evidence of presence in human semen but that are part of viral families in which other members have been detected in human semen

•Measles virus (paramyxovirus)
•Japanese encephalitis virus (flavivirus)
•Tick-borne encephalitis virus (flavivirus)
•Omsk haemorrhagic fever virus (flavivirus)
•Alkhurma haemorrhagic fever virus (flavivirus)
•Spondweni virus (flavivirus)
•Machupo virus (arenavirus)
•Junin virus (arenavirus)
•Lujo virus (arenavirus)
•Sabia virus (arenavirus)
•Guanarito virus (arenavirus)
•Lymphocytic choriomeningitis virus (arenavirus)
•Haemorrhagic fever with renal syndrome virus (hantavirus)
•Heartland virus (phenuivirus)
•Phlebotomus fever virus (phenuivirus)
•Hendra virus (paramyxovirus)
•Parainfluenza virus (paramyxovirus)
•Respiratory syncytial virus (paramyxovirus)
•Orf virus (poxvirus)

Viruses detected in animal semen but with no studies on presence in human semen

•Middle East respiratory syndrome coronavirus (dromedary camel)
•Japanese encephalitis virus (pig)
•Spondweni virus (mouse)
•Foot-and-mouth disease virus (pig, cow)
•Parainfluenza virus (cow)
•Paravaccinia virus (cow)

We also listed the viruses for which published evidence of sexual transmission or detection in the human male reproductive tract exists, without published evidence of their presence in human semen, such as Crimean–Congo haemorrhagic fever virus. Some viruses, such as Japanese encephalitis virus⁷⁰ and Middle East respiratory syndrome coronavirus,⁷¹ have been detected in the semen of their animal hosts, but have not been studied in human semen.

Finally, we listed several important viral pathogens that cause acute infection in humans within the same families of viruses that have already been found to persist in human semen. In this regard, investigation of measles virus and Japanese encephalitis virus are of particular importance.

This Review has clear implications for clinical and public health practice and policy. First, viral persistence in semen following acute infection can lead to sexual transmission, driving or contributing to ongoing transmission. For example, transmission through sexual networks was the key driver in the unprecedented and unexpected global outbreak of mpox.³ Viral reservoirs in semen can also lead to resurgence when an outbreak is believed to have ended and preventive measures have been scaled back. Viral transmission from a latently infected survivor who was unknowingly shedding viable Ebola virus in his semen led to the resurgence of Ebola in Guinea in 2016⁷² and again in 2021.⁷³

Knowledge of viruses that can persist in semen enables clinicians and public health authorities to implement appropriate strategies and develop evidence-based guidelines to reduce transmission, for example through health education, recommendation of barrier-type contraception, and semen clearance testing. Availability of high-quality evidence is not only important to make appropriate recommendations but also to instil trust in the affected individuals and the public. For example, in the first months of the global mpox outbreak, when data on the presence and persistence of monkeypox virus in semen were still scarce, the UK Health Security Agency precautionarily recommended the use of condoms for 12 weeks after infection.⁷⁴

The presence of virus and concomitant local inflammation in the male reproductive tract can heighten susceptibility to sexually transmitted infections.⁷⁵ In addition, inflammation and spermatogonial stem-cell infection can have consequences for male fertility.⁷⁶ As seen with Zika virus, viral presence in semen can lead to embryonic infection, which can increase the risk of miscarriage or congenital malformations.⁷⁷^,⁷⁸

Furthermore, viral persistence in semen has implications for development of therapeutics and vaccines. Not all drugs are competent at crossing the blood–testis barrier, and thus, the virus can be cleared from the blood but would persist in semen. The virus establishing persistent infection in immunologically privileged sites can also be genetically distinct from the virus in blood,⁷⁹ a fact that needs to be considered when choosing the viral target for therapeutics (particularly, monoclonal antibodies) and vaccines.

In conclusion, many viruses and virus families can persist in human semen following acute infection, and some of these viruses have evidence for sexual transmission. Establishment of latent infection in the male reproductive tract and virus shedding in semen is probably more common than currently considered, extending to viruses not known to cause symptomatic infections in the male reproductive tract, such as orchitis or epididymitis, and viruses that are not traditionally considered to be sexually transmitted. An improved understanding of the role of semen in virus transmission is of great value for public health, most notably in the response to outbreaks of high-consequence viral pathogens.