JavaScript is not available.

Zika virus outbreak What you need to know

The Zika virus was virtually unheard of until recently. But links to birth malformations, and a prediction that 4 million people could be infected this year, have led to the World Health Organization declaring it an international public health emergency. We take a look at the risks, the issues and whether there are any solutions.

What is the Zika virus?

Zika is a virus transmitted by Aedes mosquitoes, which are found in tropical regions. Typical symptoms include a fever, headache and rash lasting for up to a week. It can also cause a mild form of conjunctivitis, which can help distinguish the illness from dengue fever, another mosquito-borne illness. In some cases it can lead to the potentially fatal Guillain-Barre syndrome, a rare condition that affects the nervous system. But with about 80 per cent of people affected not showing any symptoms, the infection is often undiagnosed.

Why is infection with the Zika virus so bad for pregnant women?

The reason for such concern is that the virus seems to affect fetuses. Since the virus arrived in Brazil last year, cases of microcephaly – a congenital condition that causes babies to be born with a small head and sometimes brain damage – have increased 20-fold. However, it isn’t yet known how many of the cases are linked to Zika infection. Nutrition, environmental conditions and additional infections, for example, could also play a role.


It can affect fetuses at all stages of pregnancy, although infection is thought to be most dangerous during the first and second trimester. Women living in Zika hotspots are being advised by governments to hold off getting pregnant, in some countries for up to two years. Some have suggested the impacts of the virus could challenge anti-abortion policies in this region.

Why have I never heard of Zika before?

Before 2000, Zika mostly infected forest animals. Human infections were rare and the virus didn’t cause any of the suspected complications we are seeing today. One theory is that it has mutated, making it capable of hijacking human cells more easily.

The Zika virus is also new to the Americas. Previously, it was limited to Africa and South-East Asia, typically in areas that are also hotspots for dengue fever. But after first making its appearance in Brazil last May, Zika has been spreading across the Americas, with 25 countries now seeing active transmission of the virus. The World Health Organization believes it will spread to all countries in the region except for Canada and continental Chile. And that could happen soon, helped by this year’s El Niño potentially increasing mosquito populations.

On 4 February, Spain confirmed a case of Zika virus in a pregnant woman – the first in Europe. The woman had recently returned from Colombia. According to the Spanish health ministry, “the diagnosed cases of Zika virus in Spain… don’t risk spreading the virus in our country as they are imported cases”.

How is the Zika virus spread?

Several species of Aedes mosquitoes are known to carry the Zika virus, including Aedes aegypti, the species that transmits dengue. Although previously limited to specific tropical regions, they now seem to be taking up residence in higher latitudes, which could be due to global warming.

Zika can also be passed on through sex. The virus has been isolated from the semen of an infected individual and has been confirmed as the transmission method for a case of Zika on the US mainland.

Is there a vaccine for Zika?

There is currently no vaccine available. It could take years to develop one, although some vaccine developers claim they could have one ready this year.

Until then, efforts are focused on relieving symptoms, if any are present, and advising against pregnancy in those at risk. Protective measures include using insect repellents and mosquito nets, wearing long-sleeved shirts and long trousers, and staying indoors.

Have there been outbreaks of Zika before?

The biggest outbreak until now affected about 28,000 people in French Polynesia in 2013 and 2014, before spreading to other Pacific islands. Following the outbreak in French Polynesia there was an unusual increase in babies born with microcephaly. In 2007, there was a smaller outbreak in Yap Island, Micronesia, where about 185 cases were identified. The Zika virus was new to both of these regions.

The virus that emerged in Brazil seems to be closely related to the strain seen in French Polynesia. One theory being debated is that travellers to the 2014 Football World Cup in Brazil may have brought the virus with them.

What is being done to control the current outbreak?

The WHO has asked for international help to develop a vaccine. Other anti-Zika initiatives involve learning more about the virus, diagnosing cases more quickly and trying to control mosquito populations with techniques including the release of genetically modified insects. While cooler, dryer weather at that time of year should reduce the mosquito population, organisers are also searching venues for standing water where mosquitoes could breed.

What’s the advice to those visiting areas affected by Zika?

Pregnant travellers are being advised to avoid countries affected by Zika, while those returning from a trip should see a doctor. Conceiving after the virus has cleared from the blood, which takes about a week, is thought to be safe, although it’s always best to seek medical advice.Health authorities in the UK are advising men who have travelled to affected regions to use condoms for a month after they return, or six months after recovery if they experience Zika symptoms.