Countries and territories with transmission of Zika virus, 2007- 2016
(Source: World Health Organisation Zika situation report February 12)

The World Health Organization (WHO) has declared the Zika virus a global public health emergency. With daily headlines about the Zika virus in the press and concerns raised over travel to affected countries in South America – in particular Brazil with the Olympics coming up – it would seem that the Zika virus is now firmly on everyone’s radar. However, only a few months ago most people in the UK had not even heard of it. So what is the Zika virus and how much of a threat does it pose?

The Zika virus is spread by Aedes mosquitoes. Researchers currently believe the Zika virus is spread mainly through mosquitoes, but other methods of transmission are being investigated. When a mosquito bites an infected person it draws blood and contracts the virus. Then if the same mosquito bites another person it can pass on the virus, thus spreading the disease. Zika virus cases had previously only been recorded in the southern hemisphere, in Africa and Polynesia, until May 2015, when the Pan American Health Organization (PAHO) issued an alert regarding the first confirmed Zika virus infections in Brazil. Since then the virus has spread rapidly in South American countries.

Most people who are infected with Zika actually show no symptoms. In fact only about 1 in 5 people will have symptoms and in most cases these are mild but can include: fever, rash, joint pain, or conjunctivitis (red eyes). Symptoms typically begin 2 to 7 days after being bitten by an infected mosquito. Most people recover quickly but the real concern is that the virus could be linked to a surge in numbers of babies being born with underdeveloped brains, a condition known as microcephaly. A link between Zika virus and microcephaly has previously been suspected but has not been fully verified by any scientific studies.

Microcephaly is when a baby is born with an abnormally small head, as their brain has not developed properly. The severity varies, but it can be deadly if the brain is so underdeveloped that it cannot regulate the functions vital to life. Children that do survive face intellectual disability and development delays. There are many potential causes of microcephaly including rubella and substance abuse during pregnancy and also genetic abnormalities. However, the sudden rise in cases of microcephaly in Brazil has raised concerns about a potential link with the Zika virus.

In 2014 Brazil had less than 150 cases of microcephaly; this has increased dramatically to more than 4,700 reported cases since October 22, 2015, with 404 confirmed and 3,670 still being investigated. Some babies who died had the virus in their brain and it has been detected in placenta and amniotic fluid too.

A similar rise in microcephaly has not been seen in other affected countries in S America yet, but the virus was first reported in Brazil and then spread to more than 20 other countries; the WHO says there will be a lag of several months to know if pregnant women in these newly infected countries are affected too. There have been suggestions that Zika led to a rise in birth defects after an outbreak 2013 in French Polynesia. The WHO says it expects to decide within a few weeks if there is a link between the Zika virus and birth defects. In the meantime many countries are advising women to delay getting pregnant until more is known.

Declaring Zika as a “public health emergency of international concern” singles the disease out as a serious global threat. People are being advised to take precautions to reduce being bitten by the mosquito and efforts are under way to kill the mosquitoes with insecticide. Research is also underway to find a vaccine to prevent the virus, and ways to reduce the mosquito numbers are also being assessed.

The Olympics are due to be held in Rio de Janeiro in August later this year. The Brazilian authorities will be targeting the mosquitoes’ breeding grounds in the run-up to the Games. The International Olympic Committee says it is in “close contact” with the Rio organisers and that Olympic venues will be inspected daily in the lead-up to and during this summer’s Games. There is also some hope there will be fewer mosquitoes in August as the month is both cooler and drier. In the meantime pregnant women are being advised not to travel to infected countries.

Rachel Kayani