Hamsters’ Testicles Shrink After Being Infected With COVID, Study Finds

The virus was delivered intranasally to the rodents, with researchers finding an acute decrease in sperm count and testosterone.
Koh Ewe
Hamsters study done by University of Hong Kong scientists show that COVID-19 could shrink and damage testicular tissue.
A study done on hamsters showed that SARS-CoV-2 infections resulted in damage to their testicles. Photo: Frenjamin Benklin, Unsplash

In news that will have alarm bells ringing for half the world’s population, a new study suggests that COVID-19 could spell trouble for testicular health, including a decrease in size, sperm count, and testosterone levels.

The research, published on Feb. 18, was conducted over recent months by researchers at the University of Hong Kong to investigate the effect of COVID-19 on hamsters' testicles.


Varying doses of SARS-CoV-2, the virus responsible for COVID-19, were intranasally delivered to hamsters—only some of which were vaccinated against the virus. The hamsters were then killed between one and 120 days after infection and their testicles examined. 

What researchers found was an “acute decrease” in sperm count and testosterone levels four to seven days post-infection in unvaccinated hamsters. Meanwhile, “damage” to the testicular tissue—including inflammation, degeneration, and necrosis—was observed as early as a week after infection and persisted in the sample collected on Day 120.

Testicular size and weight were also found to be reduced after infection. Hamsters that were vaccinated against the virus did not exhibit testicular damage. 

“SARS-CoV-2 can cause acute and chronic testicular damage in hamsters and is consistent with the anecdotal reports of clinical orchitis and hypogonadism in recovered COVID-19 [human] males,” concluded the authors of the study, which has been accepted for publication by the peer-reviewed journal Clinical Infectious Diseases.

“Long term follow-up of sperm count and sex hormone profile of convalescent COVID-19 males is warranted.” 

Hamsters are commonly used in COVID-19 studies as their bodies’ reactions to respiratory viruses are similar to humans. Richard J. Sugrue, associate professor of virology at Singapore's Nanyang Technological University, told VICE World News that experiments on hamsters are able to “provide useful information about the progression of virus pathogenesis.” 


However, Sugrue noted that while hamsters are helpful in studying virus infections, they remain biologically different from humans in significant ways. 

“Any results obtained with the hamster model would therefore need to be treated with caution when they are applied to human disease,” he said. “The animal model work would be the first step and the results obtained would then need validation using human clinical studies and materials.”

Testicles have been found to be sanctuaries for diseases such as HIV, Ebola, and Zika, where viruses can enter and linger for years without being detected by the immune system.

SARS-CoV-2 targets angiotensin-converting enzyme 2, a type of protein found in the testicles that’s believed to be the receptor of the virus. Other viruses in the SARS-CoV family have been suspected to cause testicular dysfunction and inflammation. However, reports differ on the susceptibility of testicular cells to COVID-19. 

Research has found that COVID significantly reduces sperm count in humans, at least in the short term. In one study, comparing median sperm count, those who were not infected by COVID had an almost five times higher sperm count in their ejaculate than those who had been infected.

The relationship between COVID and erectile dysfunction is also being investigated, with a study involving 100 men in Italy—of which 25 were COVID-positive and 75 negative—finding a positive correlation.


Researchers at the University of Miami theorized that erectile dysfunction that coincided with COVID infection was a result of restricted blood flow to the penis. Others point to the psychological impact of getting COVID—such as stress and depression—as a potential cause of erectile dysfunction.

Of all the reported side effects of COVID—which range from a prolonged loss of taste, to brain fog—how the virus affects male genitals and fertility remains among the topics of greatest public discussion. 

Rapper Nicki Minaj stirred controversy last year with an out-of-pocket tweet suggesting that the COVID vaccine could result in impotence, citing a friend of her cousin in Trinidad and Tobago. Following global backlash against her viral tweet, the White House offered to address Minaj’s queries about the COVID vaccine, while Trinidad and Tobago’s health minister dismissed her claims as false. 

In January, a man told Slate about his penis shrinking more than an inch after contracting COVID—though for now he appears to be the only one claiming this rare side effect. However, men have been reporting post-COVID testicular pain as early as 2020, while a 2021 study found that testicular pain was more frequently observed among hospitalized COVID patients.

Follow Koh Ewe on Twitter and Instagram.