Covid can cause acute testicular damage in hamsters, might affect male fertility, study says

Scientists say testicular damages observed in study could be prevented by vaccination

Infection with the novel coronavirus causes damage to testicles in hamsters and associated hormonal changes, according to a new study that has called for better long-term follow-up studies of fertility in recovered Covid-19 patients.

Researchers, including those from the University of Hong Kong, assessed the gradual immunological, pathological and hormonal changes in hamster testes following infection with the novel coronavirus SARS-CoV-2 and its variants.

They used influenza virus A(H1N1)pdm09 which was behind the 2009 swine flu pandemic as the control for the study to compare the effects.

While respiratory tract infection in the hamsters was limited following SARS-CoV-2 inoculation, scientists found that the virus led to acute decrease in sperm count, serum testosterone up to a week post infection, and subsequently reduced testicular size and weight.

The study, published on Friday in the journal Clinical Infectious Diseases, found several signs of reproductive tissue damage in the infected hamsters.

“Acute histopathological damage with varying degree of testicular inflammation, haemorrhage, and necrosis, degeneration of seminiferous tubules and disruption of orderly spermatogenesis were seen with increasing virus inoculum,” the scientists wrote in the study.

On the contrary, they said controlled intranasal or intra-testicular infection with the flu virus showed no testicular infection or damage.

However, the scientists also pointed out that such testicular damages can be prevented by vaccination.

Over the course of the pandemic, researchers across the globe have found that while Covid-19 is primarily a respiratory disease, the novel coronavirus also infects tissues outside the lungs such as those involved in sense of smell and taste, as well as cells in the reproductive tract.

An earlier study had found evidence that one in 18 SARS-CoV-2 infected volunteers experienced discomfort in the epididymis – a long coiled tube that lies above and behind each testicle.

Another study, conducted post-mortem in Covid-19-infected males, found signs of inflammation of one or both testicles.

Previous research has also found that the ACE2 receptor proteins – which the novel coronavirus uses as a doorway to enter human cells – is not only present in the lungs, but also in cells of the reproductive system, such as in spermatogonia, Sertoli and Leydig cells.

However, it has remained unclear whether infection with the novel coronavirus can cause direct damage to testicles.

In the study, scientists inoculated eight-ten weeks old hamsters with different doses of the wild-strain of the novel coronavirus as well as Delta and Omicron variants, using the influenza strain A(H1N1)pdm09 as control.

The rodents were then sacrificed for analysing their organs and tissues at 1, 4, 7, 42, and 120 days post-infection.

Researchers found that sperm counts were “significantly reduced” in all the hamsters infected with the higher doses of the virus after 4 days, despite the absence of pathological changes in appearance, size, or weight of their organs.

At 120 days post-infection, scientists observed marked reduction in size and weight of the testes, and sperm counts were also “significantly reduced” at 42 and 120 days following infection.

However, the study found that hamsters immunised with two jabs of inactivated whole virus vaccine with doses 14 days apart showed no signs of testes tissue damage, indicating vaccination “effectively protects testes from SARS-CoV-2 infection.

While the new findings are limited to hamsters, scientists believe long-term follow-up of sperm count and sex hormone profile of recovered Covid-19 males is warranted.

“Awareness of possible hypogonadism and subfertility is important in managing convalescent COVID-19 males,” they wrote in the study.