The World Health Organisation has declared the Zika virus an international public health emergency, prompted by growing concern that it could cause birth defects. Until recently, global health officials paid little attention to the Zika virus that circulated in the same regions as Dengue and Chikungunya viruses. It is estimated that four million people could be infected by the end of the year. Pregnant women have been urged not to travel to about 24 countries, mostly in the Caribbean and Latin America, where the outbreak is growing. Zika infection appears to be linked to the development of unusually small heads and brain damage in newborns.
What is the Zika virus?
The Zika virus is a mosquito-transmitted infection related to dengue, yellow fever and West Nile virus. Although it was discovered in the Zika forest in Uganda in 1947 and is common in Africa and Asia, it did not begin spreading widely in the Western Hemisphere until last May, when an outbreak occurred in Brazil.
Until now, almost no one has had major infections from Zika. Few have had immune defenses against the virus, so it is spreading rapidly. Millions of people in tropical regions of the Americas may have been infected. Scientific concern is focused on women who become infected while pregnant and those who develop a temporary form of paralysis after exposure to the Zika virus.
How is the virus spread?
Zika is spread by mosquitoes of the Aedes genus, which can breed in a tiny pool of water and usually bite during the day. The aggressive yellow fever mosquito, Aedes aegypti, has spread most Zika cases. The mosquito is found in Nigeria and some other countries.
What is the danger?
Zika causes brain damage in infants. Experts aren’t certain how it happens, or even whether the virus is to blame. The possibility that the Zika virus causes microcephaly – unusually small heads and damaged brains – emerged only in October 2015, when doctors in northern Brazil noticed a surge in babies with the condition.
What is microcephaly?
Babies with microcephaly have unusually small heads. In roughly 15 percent of cases, a small head is just a small head, and there is no effect on the infant, according to experts.
But in the remainder of cases, the infant’s brain may not have developed properly during pregnancy or may have stopped growing in the first years of life. These children may experience a range of problems, like developmental delays, intellectual deficits or hearing loss.
What countries are affected?
Pregnant women are urged to avoid about 24 destinations mostly in the Caribbean, Central America and South America.
It’s often a silent infection, and hard to diagnose. Until recently, Zika was not considered a major threat because its symptoms are relatively mild. Only one of five people infected with the virus develop symptoms, which can include fever, rash, joint pain and red eyes. Those infected usually do not have to be hospitalized.
What are the tests?
There is no widely available test for Zika infection. Because it is closely related to dengue and yellow fever, it may cross-react with antibody tests for those viruses. To detect Zika, a blood or tissue sample from the first week in the infection must be sent to an advanced laboratory so the virus can be detected through sophisticated molecular testing. The Centres for Diseases Control and prevention, CDC, testing algorithm for pregnant women who have visited countries in which the Zika virus is spreading.
Most of those who get the virus do not feel ill — and there is no evidence that babies are hurt only when the mother has been visibly ill. But at the time the guidelines were issued, the CDC and state health departments simply did not have the laboratory capacity to test every pregnant woman who visited Latin America and the Caribbean in the last nine months, as well as every pregnant woman in Puerto Rico.