|A lab mouse. Picture via Pixabay|
A new study is causing quite the stir. Researchers used a mouse-adapted African strain of Zika to examine if the virus damages the testicles, as Zika has been detected in the sperm for up to 10 weeks post infection. In this latest study, severe damage and significantly smaller testicles were observed in infected mice. By day 21 the damage was much more extensive. Starting at day 14, sperm count and sperm motility dropped and by day 42, the differences were large. Overall, the fertility of infected mice dropped from around 80% to roughly 25% and the number of viable fetuses from the sperm of infected males dropped from 25 (from uninfected sperm) to 10. The researchers also tested this with mice infected with Dengue and an isolate of the Asian strain of Zika, but Dengue didn't damage the testes and the Asian strain caused less damage. The researchers hypothesize that the difference seen between the African and Asian strains is due to the Asian strain not being adapted to mice whereas the African strain was (it replicated less efficiently than the African strain in the mouse model).
|Mouse testicles either infected with Zika or not, after 7 (a), 14 (b) or 21 days (c) post infection. Adapted from Govero et al., 2016; doi: 10.1038/nature20556|
This study, although valuable, does have some limitations. First, a mouse-adapted strain was used which could result in mutations that make the virus different than the ones circulating in humans. Second, the work was done in a mouse model and sometimes research in mice doesn't translate to humans. However, this was just a preliminary study and something of concern was noted. These findings more than justify further work to examine if Zika causes damage to human testicles and if it can reduce fertility.