More than 50,000 people have been infected with monkeypox in the recent outbreak, including a notable number of sexually active gay men. Now, a study of macaques suggests that the monkeypox virus can also affect, and is present in, the testicles and sperm. The researchers detected the virus in both the testicular tubules and in cells involved in sperm production. Some of the monkeys continued to carry the monkeypox virus more than a month after the acute infection. According to the scientists, this suggests that the monkeypox viruses in the testicles are at least partially protected from the immune system – and that they can also be sexually transmitted to humans.
Monkeypox is actually a very rare disease in humans and is mainly limited to Africa. In west and central Africa, where the monkeypox virus is native, small outbreaks occur when people there come into close contact with an infected rodent or monkey. Unlike the corona virus, the monkeypox virus cannot be transmitted via aerosols, but only through direct contact with body fluids such as blood and saliva or the viruses contained in the skin pustules and their crusts. But since the beginning of May 2022, there has been a global increase in monkeypox cases for the first time, more than 50,000 people in 120 countries outside of Africa have been infected. A striking number of those affected are young men, in whom the skin lesions were mainly found in the genital area. The information they provided about possible contacts raised the suspicion that they had been infected through sexual contact.
Virus in testicular tissue and epididymis
For their study, Jun Liu and his colleagues from the US Army Medical Research Institute of Infectious Diseases (USAMRIID) in Fort Detrick examined the frozen testicles of 21 long-tailed macaques (Macaca fascicularis) that had previously been infected with the monkeypox virus for experimental purposes. This monkey species is considered to be a well-suited animal model for this viral disease because it reacts similarly to humans, even if the infection is usually more severe in it than in us humans. “We examined tissue samples from the acute phase of the infection as well as from the convalescence phase, in which the infection gradually subsides,” explains senior author Xiankun Zeng. To detect the presence of monkeypox viruses, the researchers used both fluorescent markers for the virus antigen and detection methods for the RNA of the virus.
The result: “We detected monkeypox virus antigens in 18 of 21 of the testicles examined,” report the scientists. The virus was therefore present in the sperm precursors as well as in the seminiferous tubules and the interstitial cells of the testicles. “We also detected monkeypox viruses in the epidymial ducts of the epididymis, which are the sites of sperm production and maturation,” the researchers said. In her opinion, this suggests that the monkeypox virus can also be transmitted via sperm and sperm fluid in the acute phase of the infection. This could explain why so many young men have become infected through same-sex sexual contact. “The testicles are involved in many viral infections, including Zika, Ebola, Marburg, and Crimean-Congo fever,” Liu and his colleagues explain. Because this organ, along with the eyes and brain, is one of those organs that are only partially accessible to the immune system.
Persistent even after the acute infection
According to the study, sexual transmission of the monkeypox virus could still take place after the superficial skin lesions and other acute signs of infection have disappeared. The team was also able to detect monkeypox in two testicle samples from macaques that were already convalescent. These persisted up to 37 days after infection. While the skin lesions of these monkeys no longer contained the virus, it was still present in the testicular tissue. “Our data thus provide evidence that the monkeypox virus can be passed on via the sperm both in the acute phase of infection and in the convalescence phase,” says Zeng. Further studies with human patients are now necessary in order to prove this persistent presence and transmission of the monkeypox virus in humans.
Quelle: Jun Liu (US Army Medical Research Institute of Infectious Diseases (USAMRIID), Fort Detrick) et al., Nature Microbiology, doi: 10.1038/s41564-022-01259-w