Is Zika infection harmful to male fertility?

Zika virus infection can break down and severely damage animals' testes and affect reproductive health of males, new research suggests.

Although the Zika virus is largely transmitted to people via mosquito bites, the virus can also be sexually transmitted from person to person and through blood transfusion.

Although it can be found in the semen of infected men, the impact of Zika on the human male reproductive system is largely unknown.

To investigate further, scientists from Washington University School of Medicine in St. Louis infected male mice with a mouse-adapted African or Asian Zika virus strain, or with the related dengue virus.

Every seven days, the researchers examined samples of mouse testes to look for damage and tested cells from those organs for evidence of the virus.

The researchers found that cells in the testes showed signs of Zika infection by day seven. After 14 days, the testes visibly shrank in size. As Zika infection progressed, the seminiferous tubules where sperm is formed began to break down.

Additionally, the researchers found that inflammatory cells mounted a response, which added to the damage caused by the virus. By 42 days after infection, damage from the virus had cut the test animals' average motile sperm count by roughly three-fold, with some mice showing very low sperm counts.

Furthermore, their levels of testosterone and inhibin b, hormones vital to regulating sperm production and testes function, also fell, showed the study published online in the journal Nature.

Low sperm and hormone levels were associated with decreased fertility rates. Longitudinal studies of sperm function and viability in men who have experienced Zika infection are needed, the researchers concluded.