In a recent study published in Nature Microbiology, researchers performed retrospective detection of the monkeypox virus (MPXV) within the testes of nonhuman primates (NHPs).

Study: Retrospective detection of monkeypox virus within the testes of nonhuman primate survivors. Image Credit: BalazsSebok/Shutterstock

Background

Close sexual contact has been related to the spread of (MPXV in the worldwide pandemic in 2022. Nevertheless, it continues to be unclear whether MPXV duplicates within the testicles or transmits through semen and leads to an energetic infection. The team retrospectively examined crab-eating macaques infected with MPXV of clade I or clade II MPXV using immunostaining and ribonucleic acid (RNA) in situ hybridization.

Concerning the study

In the current study, researchers examined MPXV infection and its persistence within the testes of infected crab-eating macaques, including MPXV-recovered macaques.

Crab-eating macaques infected with MPXV on the team’s institute were utilized to look at the pathogenesis of human MPVX or in its place animal model to review smallpox. MPXV infection was detected by screening formalin-fixed paraffin-embedded (FFPE) testicular, prostatic, and epididymal tissues from 21 male crab-eating macaques that died inside six to 13 days of MPXV exposure via IT, IV, or AS inoculation route, without therapeutic intervention. This facilitated the understanding of the potential for MPXV infection within the testes and shedding into semen.

The team created an RNA in situ hybridization (ISH) assay to discover the MPXV-specific transcript D1L, which causes smallpox. The study hypothesized that MPXV might linger within the testes of NHP survivors. Moreover, the testicular tissues collected from 20 crab-eating macaques that had withstood the MPXV challenge without medical treatment were screened.

Results

 The team observed that 18 out of 21 animals possessed MPXV antigen of their testes, including 14 out of 16 animals with the clade I strain of MPXV and 4 out of 5 animals with the clade I strain. In seven of the 18 animals, the team detected the MPXV antigen within the epididymis, while six out of the 21 had MPXV antigen of their prostate glands. In comparison with the uninfected control testicular tissue, MPXV antigen staining was multifocal and largely present in the testes’ interstitial tissue.

Intriguingly, MPXV antigen was occasionally present in the inflammatory cells and spermatozoa or in cellular debris present within the seminiferous tubules, which house sperm production in addition to immune privilege. MPXV antigen was largely present in the duct epithelium and the lamina propria of the epididymis. Remarkably, MPXV antigen was also present in degenerated spermatozoa, cellular debris within the epididymal duct lumen, or inflammatory cells. Within the regions of inflammation observed within the prostate of six of 21 animals, immunohistochemistry (IHC) staining was multifocal or focal.

The team employed antibodies to perform immunofluorescence staining on alpha-smooth muscle actin (SMA) and MPXV to point out that these MPXV had spread to the lumen of the epididymal ducts and the seminiferous tubules of the testis, that are crucial for the generation, maturation, and transportation of sperm. These findings imply that MPX virions could also be released within the semen in the course of the acute stage of the infection in crab-eating macaques, albeit additional verification requires viral isolation from semen.

Two of the 20 survivors with testicular tissues stained positively by IHC survived to the top of the trial and their scheduled death. Crab-eating macaques that survived MPXV exposure typically displayed scabbed skin lesions around 20 days following infection with a viral deoxyribonucleic acid (DNA) level below the detection threshold. On the face, tail, arms, feet, and/or back, these two survivors often had scabs in addition to desquamated or healed skin sores.

The necrotic seminiferous tubules present within the two survivors’ testes, in addition to the necrotic center area of granulomas, were the foremost sites of IHC staining signal detection. Excluding one survivor’s lung and the opposite survivor’s tracheobronchial lymph node and skeletal muscle, the IHC staining signal was not seen within the skin lesions or in the opposite organs. Moreover, MPXV-specific RNA ISH provided additional evidence of infection within the testicular granulomas. Along with largely non-cell associated viral antigen within the necrotic center of granulomas, a small variety of CD68+ monocytes/macrophages near the necrotic areas also contained viral antigen.

The necrotic patches were also surrounded by lymphocytic, plasmacytic, and neutrophilic inflammation, as shown by the abundance of CD68+ monocytes/macrophages, CD3+ T cells, and myeloperoxidase (MPO)+ neutrophil granulocytes. Interestingly, CD8+ T cells account for a lot of the CD3+ T cells. These findings suggested that MPXV may have the opportunity to persist, especially in areas of inflammation and necrosis, within the testes of recovering crab-eating macaque survivors.

Our data provide evidence that monkeypox virus could also be shed into semen during each acute and convalescent stages of the disease in crab-eating macaques.”

Conclusion

Overall, the study findings showed that crab-eating macaques may shed MPXV into their semen during each acute and convalescent stages of the infection.