The researchers found that Covid-19 may cause damage to the patient's kidneys and testicles. They found data on the clinical features of three groups, one with six patients and the other with 99 and 41 patients, respectively. Data show that 3%-10% of patients have abnormal renal function, and 7% have acute renal insufficiency. Patients with COVID-19 may develop orchitis, researchers say. For recovered male patients with fertility needs, it is best to check the reproductive system in the hospital.

Evenson et al. studied the characteristics of human sperm chromatin structure after influenza hyperthermia, finding that influenza may have potential effects on sperm chromatin structure, which may lead to the short-term release of abnormal sperm.

In addition, a study by the Boston University School of Public Health showed that men infected with the new crown are associated with a temporary reduction in fertility. At the same time, the researchers found a short-term decline in fertility (comparing the probability of conception per cycle between infected and uninfected people) due to the following two reasons.

1. Having a fever after a COVID-19 infection.
2. Immune and inflammatory responses in the testis and epididymis (observed in hospitalized patients with COVID-19).

Early in the COVID-19 pandemic, researchers discovered a peculiar phenomenon: SARS-CoV-2 was less common among children. Although the proportion of male and female infections is equal, the severe cases and the infection severity in males are significantly higher than in females.

In a document published by Nature Medicine, through a large-scale sample survey (average age 43.8 years old, deliberately excluding the elderly) and a comparative study of positive and negative samples, researchers found that the most common symptoms of COVID-19 were fatigue, shortness of breath, muscle pain, joint pain, headache, cough, chest pain, change in smell and taste, and diarrhea. Some patients also developed new symptoms, such as hair loss, sneezing, male dysfunction, etc., and even had similar symptoms after recovery.

Everything has a reasonable explanation after the research made it clear that ACE2 is the receptor for the SARS-CoV-2 virus to invade the host cell, and the protease TMPRSS2 is the cutting enzyme to help the virus invade the cell.

Angiotensin-converting Enzyme 2 (ACE2) exists in large quantities in testicular tissue and has a high expression level in somatic and germ cells such as seminiferous duct cells, Leydig cells, Sertoli cells, and spermatogonia. However, patients over 60 showed relatively low expression levels and were less prone to testicular damage.

The serine protease TMPRSS2 performs protein cleavage and hydrolysis to help the fusion of the viral outer membrane and the cytomembrane, enabling the virus to invade cells smoothly. TMPRSS2 expresses in all cell clusters within the testis.

Because the receptor ACE2 and serine protease TMPRSS2, which the virus invades human cells, are highly expressed in the male reproductive system cell clusters, the symptoms of men infected with COVID-19 are more severe, and their fertility and sexual function are affected. Effects include but are not limited to symptoms of erectile dysfunction (ED), penile pain, reduced testicular volume, low testosterone levels, orchitis, epididymitis, seminal vesicle discomfort, cavernous body damage, decreased libido, decreased sperm count, and decreased quality. And men aged 30 to 60 are more likely to be affected than younger and older men, and a small number of patients also have the SARS-CoV-2 virus in their semen.

In another study, in February 2022, a team from the University of Hong Kong found that even if hamsters were infected with a moderate amount of the new coronavirus, symptoms such as acute testicular injury, chronic testicular atrophy, and a decrease in serum testosterone would occur, and the side effects will still exist after recovery.

The researchers vaccinated the SARS-CoV-2 virus intranasally or directly into the testes using the influenza virus H1N1 as a control, finding that although the hamsters infected with COVID-19 did not suffer from severe illness, their sperm count and testosterone levels increased sharply within 4-7 days after infection. 

42-120 days after infection, the testicles shrank, the size and weight showed an asymmetric decline, androgen levels dropped significantly, and the testicular tissue was inflamed. However, the control group hamsters infected with the influenza virus H1N1 had no significant decrease in their associated fertility.

At the same time, the researchers used the Delta strain and Omicron strain variants to conduct intranasal inoculation experiments on hamsters and found that three hamsters infected with Delta or Omicron strains became mutated 4-7 days after infection. 

Two hamsters in the body had degeneration and necrosis of seminiferous tubules in different degrees, indicating that different types of SARS-CoV-2 have damaged the reproductive system of hamsters. However, the H1N1 influenza virus does not cause similar damage. Vaccination effectively protects the testes of hamsters from infection and lesions by SARS-CoV-2.

After recovery from COVID-19 and a human spermatogenic cycle, two and a half months, men can produce sperm. When a large amount of sperm accumulates in the epididymis, a man can give birth. But it is worth noting that half a year after being infected with the new crown, the level of testosterone produced by the testicles is still low. Therefore, it may take more than 3-6 months for patients with COVID-19 to recover. During the recovery, patients should have a healthy routine and diet to restore reproductive function.

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