Zika is a mosquito-borne virus that is harmless to the vast majority of people who contract it, many of whom display no symptoms. But it can cause complications for the children of pregnant women. Zika has been associated with the condition known as microcephaly, in which babies have abnormally small heads.

There is concern that Zika may trigger Guillain-Barré syndrome (GBS) in a small number of victims of the virus. This rare condition involves a person’s own immune system damaging the nerve cells, causing muscle weakness and sometimes paralysis.

Some evidence has also emerged of a possible risk to male fertility. A study published in Nature looked at the effects of Zika on fertility in mice. When infected with a strain of the virus, some mice developed shrunken testicles, low testosterone levels and low sperm counts. The researchers believe the damage may be irreversible.

The current outbreak of Zika has spread widely across tropical regions, particularly in Latin America. The World Health Organization says: “The geographical distribution of Zika virus has steadily widened since the presence of the virus was confirmed in October 2015.”

A rigorous regime of avoiding mosquito bites is the best protection against Zika, as well as other more common diseases spread by mosquitoes in the tropics.