The human testes as sanctuaries for viruses - Hindustan Times
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The human testes as sanctuaries for viruses

Mar 02, 2022 08:15 PM IST

They are known to provide safe harbours from attacks by the body’s immune system. What does this mean for viruses like Covid-19 and Ebola? 

In November 2014, a 26-year-old Indian male landed in New Delhi airport after surviving the Ebola virus disease (EVD). He had contracted Ebola in September and was treated at a Liberian hospital and declared free of the disease.

Scientists must urgently answer whether these infections are sexually transmissible, how often and how long that happens, and who is at risk.(Pixabay)
Scientists must urgently answer whether these infections are sexually transmissible, how often and how long that happens, and who is at risk.(Pixabay)

He underwent screening on arrival at New Delhi airport and his blood samples were negative for Ebola. However, his semen samples tested positive, and he was quarantined for three months in the airport due to the potential risk of sexual transmission. As a public health physician, I was asked at an international conference in India for my opinion on the quarantine decision. I replied that the scientific recommendation was to abstain from sexual activity for at least six months, but that each country would have to decide on quarantine based on its own regulations.

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The human testes (or testicles) have been known to provide safe harbours from attacks by the body’s immune system (called immune privilege) for several deadly viruses including HIV, Marburg, and Zika. The evolution of this safe harbour has its roots in the testicular environment being able to protect its sperm cells from an attack by the body’s immune system.

While most of the body’s cells are recognised as "self", mature sperm cells are recognised as "foreign" because of the chemical triggers they emanate. Such a defence mechanism is akin to the testis protecting the sperm by disguising them as non-invaders. In fact, the occasional loss of this immune privilege results in autoimmune male infertility because the sperm cells are attacked by the body.

Besides the testis, immune shielding is also present in the eye, brain, and placenta because these sites are important for survival and reproduction. The list of pathogens using these sites is growing, and most recently, Sars-CoV-2 was added to the list. In the testis, immune shielding occurs because a wall of cells forms the blood-testis barrier which prevents immune cells from moving from the blood into the tubes where sperm are made.

The shielding is a double-edged sword — while it may be good for the sperm, pathogens have figured out it’s a good hiding spot for them too. Dr Avirat Vaishnav, a pediatric urologist at the Royal Hospital Muscat, notes that some of these pathogens, like the mumps and Marburg viruses, also damage parts of the testis. The testicular environment may be thought of as an underworld refuge for notorious viral gangsters who use and abuse the place because the children living here too must be shielded from attacks by the immune police. However, in a replay of the eternal Tom and Jerry cat-and-mouse game, scientists are also working on anti-viral drugs which will bridge the blood-testis barrier and neutralise the viruses.

A recent study of non-vaccinated men who died of Covid-19 complications suggests the testes may be a sanctuary for the Sars-CoV-2 virus. While the study, published in medRxiv, is yet to be peer-reviewed, the findings are potentially grim. The author, Dr Costa, has noted that “the virus was active in the patient's testis after a long period of infection, indicating that the testis is able to maintain the viable virus for extended periods. It happens for many kinds of viruses in this genital organ”. The findings were noted in animal studies too and raise questions about consequences for reproductive health among those infected.

These consequences include whether Covid-19 can be transmitted through the semen, and the long-term impact on fertility. The authors showed that the longer the severe condition, the lower the number of surviving germ cells, that there was a fluctuation in several essential testicular genes, and that testosterone levels are 30 times reduced in the testes of Covid-19 patients. Other researchers have noted that, after an initial decline in sperm quality, patients recovered from Covid-19 reestablish their sperm quality after three months of infection.

What are the implications for the general public? They need scientists to urgently answer whether these infections are sexually transmissible, how often and how long that happens, and who is at risk. In the case of Ebola virus disease, the Centers for Disease Control and Prevention recommends avoidance of contact with blood and body fluids of people who are sick.

Also, avoidance of contact with semen from a man who has recovered from the disease, until testing shows that the semen is virus-free. Couples who wish to have children may have to be warned that sperm quality may be sub-optimal in the first three months after infection.

If a patient were to ask me what to do about these potential reproductive risks, I would recommend out of an abundance of caution that, in addition to vaccines, condoms and face masks should be used per existing public health guidelines. When used correctly, they are simple and low-cost prevention methods in this increasingly unpredictable viral world.

V Ramana Dhara is a physician who explores links between the environment and health. He is a former member of the International Medical Commission on Bhopal

The views expressed are personal

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