London - The Independent's science editor takes a look at the Zika virus.
What exactly is Zika virus?
It is a mosquito-transmitted virus closely related to the viruses that cause feverish illnesses such as dengue, yellow fever and West Nile disease. It has been known about since the 1950s, and named after the Zika Forest near Lake Victoria in Uganda where it was first isolated in 1947 from a captive monkey. It has since spread across equatorial Africa and, more recently, to Asia, Pacific Polynesia and now South America.
It has closely followed the spread of another mosquito-borne virus called Chikungunya and is transmitted by the Aedes group of mosquitoes, although it is not yet known whether other mosquitoes can carry it.
Why is it dangerous?
It is not particularly dangerous to anyone other than pregnant women. Symptoms include fever, rash, joint pains or conjunctivitis - red eyes. Many people might not realise they were infected and recover after two to seven days of being infected. However, there is growing evidence of a causal link between Zika virus infection in pregnancy and births of a congenital disorder called microcephaly, where the brain of the developing foetus fails to grow normally and babies are born seriously deformed. There is no vaccine or treatment for Zika virus.
What's the evidence that it causes microcephaly?
There is no definite proof as yet. But Brazil has experienced an explosive growth in cases of microcephaly and Zika transmission. Normally, Brazil reports about 200 microcephaly births a year, but since last October, it has seen nearly 4,000 reported cases, mostly concentrated in the poorer region of Pernambuco in the north east where between one and two percent of newborns now have microcephaly - the normal rate is about 0.07 percent. At about the same time, the Zika virus has spread rapidly throughout Brazil. But scientists have also seen an increase in microcephaly in other regions of the world where Zika has recently arrived, such as Yap Island in Micronesia in 2007 and French Polynesia in 2013-14 where many foetuses with microcephaly had been aborted.
How far is the Zika virus likely to spread?
Wherever there is mosquito-borne transmission of dengue, there is a possibility the Zika virus may also spread. In the Americas this means from Florida and the US-Mexican border region to the southern tip of Brazil. There is minimum risk of Zika being transmitted by mosquitoes in Britain or northern Europe. Zika transmission is ongoing in Brazil, Colombia, French Guiana, Guatemala, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Puerto Rico, Suriname and Venezuela, says the US Centres for Disease Control and Prevention (CDC).
What should women who are planning to go to these countries do?
Health authorities suggest women in any stage of pregnancy, or who think they might be pregnant, should re-consider their travel plans. CDC states: “Pregnant women in any trimester should consider postponing travel to the areas where Zika transmission is ongoing. Pregnant women who did travel to one of these areas should talk to their doctor.” For those who do travel, they are strongly advised to minimise the risk of mosquito bites by using insect repellent and wear clothing that minimises skin exposure. Women living in these countries are advised to postpone pregnancy.
What does the future hold?
So little is known about Zika virus, and how it may cause microcephaly, that scientists are anxious to learn more. They said the best case scenario is once people are exposed to the virus they develop immunity, which means that it just becomes another childhood infection. The immediate problem is to protect uninfected women who are pregnant or about to get pregnant.
The Independent