Researchers have found that hamsters’ COVID-19 infection causes many undesirable effects on their reproductive organs.

The infection causes the testicles to shrink, sperm counts drop, and testosterone levels drop. The study, published Friday in the journal Clinical Infectious Diseases, was conducted at the University of Hong Kong.

The researchers infected hamsters through the nose with varying doses of “Covid-19” to examine the effect on their reproductive organs. Only some of them were grafted. The animals were then killed between one and 120 days after infection, and their testicles were examined.

The study reported a “sharp drop” in sperm count and testosterone levels four to seven days after infection in unvaccinated hamsters.

The researchers observed constant inflammation in the testicle, bleeding and necrosis, in addition to degeneration of the tubes inside the organ. Changes were observed as early as a week after infection, and persisted in the sample collected on day 120.

Affected hamsters also experienced a decrease in the size and weight of their testicles. A local reporter shared search images showing the observed reduction in size.

The study authors concluded that “SARS-CoV-2 can cause acute and chronic testicular damage in hamsters, and is consistent with anecdotal reports of clinical orchitis and hypogonadism in males infected with the emerging coronavirus.”

The researchers suggested that a long-term follow-up study might look at the sperm count and sex hormone profile of men who have recovered from Covid.

While hamsters are useful in monitoring the impact of viruses such as Covid-19, and are routinely used in studies of respiratory viruses, the biological difference between them means that the results of this study may not reflect human reactions to the coronavirus.