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Zika virus damages mouse testes and sperm

07 November 2016

By Dr Barbara Kramarz

Appeared in BioNews 876

Zika virus causes permanent damage to the testes of male mice, reducing sperm count and sex hormone levels, according to a study.

'While our study was in mice – and with the caveat that we don't yet know whether Zika has the same effect in men – it does suggest that men might face low testosterone levels and low sperm counts after Zika infection, affecting their fertility,' author Dr Michael Diamond of Washington University School of Medicine, Missouri, told CNN.

Zika is mainly transmitted through mosquito bites, but live virus can remain and even proliferate in male testes for months, and can be transmitted sexually.

As mice are not normally susceptible to Zika virus, the scientists first suppressed their immune system and then infected male mice with either of two different strains of Zika virus, one of which was adapted to replicate more efficiently in mice.

The study found that Zika virus mainly destroys sperm precursor cells and Sertoli cells, which do not regenerate and which protect precursor sperm throughout development. The virus was detected in testes within a week of infection, and a decrease in testicle size was apparent after two weeks.

As the infection progressed, more damage to the testes tissue was caused by inflammation by the immune system. The mouse-adapted strain caused the most severe symptoms, where after three weeks testes had shrunk to one-tenth of their normal size.

After six weeks, even though the virus had cleared the bloodstream, motile sperm was reduced by around three-fold, and reproductive hormone levels had fallen.

'We don't know what proportion of infected men get persistently infected or whether shorter-term infections also can have consequences for sperm count and fertility,' Dr Diamond said to CNN. 'These are things we need to know.'

Experts in the field of male fertility who were not involved in this work have urged caution in interpreting these results. Dr Peter Barlow from British Society for Immunology, said: 'It is worth noting that when another strain of Zika virus was compared, one that did not replicate well in mice, the damage to the testes was not as serious. It is not currently known if all strains of Zika virus would have the same effects.'

Furthermore, Professor Richard Sharpe, an expert in male reproductive health from the University of Edinburgh, emphasised that 'viruses can show highly species-specific effects', therefore more work is required to determine whether human males are similarly affected.

This study is the first to suggest that Zika infection can lead to male infertility. It was published in Nature.

Eurekalert (press release) | 31 October 2016
CNN | 31 October 2016
The Telegraph | 31 October 2016
Nature | 31 October 2016


20 March 2017 - by Annabel Slater 
The US Centers for Disease Control has identified a potential risk of Zika virus transmission from donor sperm in the Florida tri-county area...
27 February 2017 - by Dr Barbara Kramarz 
The Zika virus reduces the size of testes in infected mice up to 21 days after infection, according to a recent study...

22 August 2016 - by Arit Udoh 
The Zika virus has been detected in the semen of a man six months after the onset of infection...
27 June 2016 - by Dr Lanay Griessner 
Researchers have pinpointed a gene that, if blocked, may stop Zika and other related viruses in their tracks...
13 June 2016 - by Ayala Ochert 
British athlete Greg Rutherford has frozen a sample of his sperm ahead of the Rio Olympics this summer because of concern over the Zika virus...
22 February 2016 - by Ayala Ochert 
The Human Fertilisation and Embryology Authority is recommending that people returning from Zika-virus prone areas should not try to conceive naturally, donate eggs or sperm, or proceed with fertility treatment for 28 days...

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