Zika virus: what you need to know

Zika virus has been all over the news, and all over the internet, for the past month. But, a lot of the information out there is confusing, conflicting or full of hyperbole, so I thought I’d round up the current situation. It’s changing all the time, but here’s what’s happening at the moment.

What is Zika? Where has it come from? Why now?

Zika is a virus, spread predominantly by the Aedes mosquito. In addition, a few cases of sexual transmission have been reported, it can be transmitted from pregnant mother to unborn child and there’s a potential for transmission via blood products. The illness it causes is usually mild – fever, joint pain, conjunctivitis, rash – and only one in five infected develop symptoms. However it now looks likely that infection in pregnancy is linked with poor pregnancy outcomes, and specifically microcephaly.

It is not a new virus. It was first isolated in Uganda in 1947 and described in a series of reports in 1952. However, the virus has largely been confined to the African continent, and thought to be the cause of sporadic outbreaks of mild illness. The first outbreak outside Africa was reported in 2007, and in May 2015, Zika was first reported in the Americas, in Brazil. Since then, it has spread rapidly, with 26 countries in the Americas now reporting cases. Here’s a really nice review of the current situation.

Why has this happened now? Well, that’s still unclear. My (semi-educated) guess that it’s largely an unfortunate set of circumstances, and a lot of increased attention. Zika has been introduced to a large country with plenty of competent vectors and a population with no existing immunity. As Zika is new to Brazil, case finding has likely been more proactive, than in parts of Africa where it has long been known to occur and thought to cause only mild illness.

It is in this atmosphere of increased testing and a large outbreak in a unprotected population, that a potential link between microcephaly and Zika has been noticed. If Zika is associated with microcephaly, then this has likely always been the case, but in isolated outbreaks in Africa pregnant women with a slight fever have not been tested, and not connected a mild illness at the beginning of pregnancy with any adverse outcomes at the end.

What’s the link with microcephaly?

The World Health Organization are clear, that currently the link between Zika virus infection during pregnancy, and microcephaly in infants is currently unproven, but considered likely. The evidence supporting this link is mounting:

  • Over the same period of the Zika virus outbreak in Brazil, an increase of mircocephaly has been seen. Between 1 and 30 January 2016, 4,783 cases of microcephaly have been reported in Brazil, compared with an average of 163 each year between 2001 and 2014.
  • Women displaying symptoms of Zika infection in early pregnancy have had babies with microcephaly, and Zika virus has been isolated from brain tissue. Here’s a case report of one such case. Warning: Details pregnancy termination etc.
  • An increase in Guillan-barre syndrome, a neurological condition, has also been noted lending evidence to the hypothesis that Zika virus can infect the brain.
  • Other viral infections are known to cause similar syndromes during pregnancy, such as cytomegalovirus and chicken pox.

What should pregnant women in the UK be aware of?

The chances of catching Zika without leaving the UK are virtually zero.

  • The current outbreak is the Americas is fuelled largely by the Aedes aegypti mosquito, though previous outbreaks have been caused by the Aedes albopictus mosquito. Although A. albopictus is common in much of Southern Europe, Aedes mosquitoes are not established in the UK. (However, there have been informal reports of Aedes albopictus sightings in the UK).
  • There have been three cases of sexual transmission reported during this outbreak, but with only seven cases of Zika reported in the UK (who had all travelled), again your chances of being infected are tiny! If in doubt, use a condom.
  • While Zika can also be transmitted through contaminated blood products, the NHS has put measures in place to prevent this.

Update: On 1 March 2016, Public Health England and the National Travel Health Network and Centre updated their advice for pregnant travellers affected by the outbreak. Here’s the latest advice.