Impotence may be one of the less-expected side effects of the coronavirus, research suggests.
Initially considered an airway infection, the coronavirus is now known to affect almost any part of the body, with some patients enduring rashes, brain fog and diarrhoea.
To better understand how the pandemic may be impacting men's genitals, a team from the University of Miami Miller School of Medicine analysed the "penile tissue" of four individuals, all of whom were due to have surgery for severe erectile dysfunction.
Two of the men were known to have overcome the coronavirus up to eight months earlier, with both having "normal erectile function" before becoming infected.
"Viral particles" were detected in the penile tissue of both the previously infected men.
Unlike the two who had never been infected, these men also showed signs of "endothelial dysfunction" – when the lining of small blood vessels does not function as it should – in the penis.
The Miami medics have warned this dysfunction could "affect the penile vascular flow", creating or worsening impotence.
"Our research shows COVID-19 [the disease caused by the coronavirus] can cause widespread endothelial dysfunction in organ systems beyond the lungs and kidneys," said study author Dr Ranjith Ramasamy.
"The underlying endothelial dysfunction that happens because of COVID-19 can enter the endothelial cells and affect many organs, including the penis.
"In our pilot study, we found men who previously did not complain of erectile dysfunction developed pretty severe erectile dysfunction after the onset of COVID-19 infection."
Impotence is thought to affect up to 55% of men aged 40 to 70. It can be caused by stress, anxiety or excessive alcohol consumption. Obesity, diabetes and high blood pressure can also be to blame.
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All the study participants, aged 65 to 71, tested negative for the coronavirus at least 24 hours before going under the knife.
Six months before the surgery, one of the men was hospitalised with coronavirus complications, while the second had experienced only mild symptoms eight months earlier.
After analysing all the men's tissue samples, the Miami medics found the two who had overcome the infection had viral particles "near penile vascular endothelial cells". The coronavirus's genetic material was also detected in these men's samples.
The medics then turned their attention to the protein nitric oxide synthase, which leads to the production of nitric oxide.
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Nitric oxide is said to be the "principal agent responsible for relaxation of penile smooth muscle", which is required for the genital to fill with blood and become erect.
Nitric oxide synthase levels were lower in the erectile tissue of the men who had overcome the coronavirus, as published in the World Journal of Men's Health.
These men also had "substantially lower" endothelial progenitor cell levels, which help blood vessel linings regenerate.
Cells in the penis are thought to express the ACE-2 receptor, which the coronavirus binds to when invading the body.
"In this report, we provide evidence of COVID-19 in the human penis long after the initial infection," wrote the medics.
"Our study also suggests endothelial dysfunction from COVID-19 infection can contribute to resultant ED [erectile dysfunction]."
The medics have stressed their study was small. They were also unable to assess the two men's erectile dysfunction before they caught the coronavirus.
Ahead of further research, the team is calling on medics to ask men with impotence if they have had the coronavirus and "investigate accordingly".
"This suggests men who develop COVID-19 infection should be aware erectile dysfunction could be an adverse effect of the virus and they should go to a physician if they develop ED symptoms," said Dr Ramasamy.
Co-author Eliyahu Kresch – a medical student – agreed, adding: "These latest findings are yet another reason we should all do our best to avoid COVID-19.
"We recommend vaccination and to try to stay safe in general."