Male mice infected with a mouse-adapted strain of Zika virus can experience tissue injury associated with decreased testis size and reduced levels of two sex hormones and of sperm cells in the seminal fluid, a Nature paper reports. Longitudinal studies of sperm function and viability in humans infected with Zika virus are needed before the potential extent and consequences of the virus for human males can be established.
In addition to transmission by mosquitoes, Zika virus (ZIKV) can be detected in the seminal fluid of affected males for extended periods of time and transmitted sexually. It has previously been shown that infecting male adult mice with ZIKV results in infection of the testes.
Michael Diamond and colleagues conducted a longitudinal study to assess the effects of ZIKV infection on the reproductive tract of male mice. The virus was detected within the testis and epididymis (a coiled tube that stores and carries sperm) of male mice within seven days of infection; after 14 days, the virus was present at high levels throughout the reproductive system of most mice.
There was a noticeable decrease in testis size and weight among ZIKV-infected animals compared to controls, as well as damage to the semen-producing seminiferous tubules of the testis and tissue injury to the epididymis. The authors also detected reduced levels of testosterone and inhibin B - two hormones important for the production of sperm, which are produced in the tubules of the testis - in infected mice. Preliminary fertility studies revealed reduced rates of pregnancy and viable fetuses from females mated with ZIKV-infected compared to uninfected male mice.
The authors stress that as these experiments were performed exclusively in mice, further work is needed to determine the extent to which, if any, these results can be translated to humans.
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