The World Health Organisation has warned that the Zika virus is "spreading explosively" in the Americas and that as many as four million people could be infected by the end of the year.
The US Centers for Disease Control and Prevention, as well as the European Centre for Disease Surveillance and Control (ECDC), have urged pregnant women against travel to several countries in the Caribbean and Latin America, where the outbreak is growing. The infection appears to be linked to the development of unusually small heads and brain damage in newborns. Here are some answers and advice about the outbreak.
What is the Zika virus?
A tropical infection new to the Western Hemisphere. 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
. Few of us have immune defences against the virus, so it is spreading rapidly. Millions of people in tropical regions of the Americas may have had it.
How is the virus spread?
Mosquitoes, but not every species. Zika is spread by mosquitoes of the Aedes species, which can breed in a pool of water as small as a bottle cap and usually bite during the day. The aggressive yellow fever mosquito,
Aedes aegypti
, has spread most Zika cases, but that mosquito is common in the United States only in Florida, along the Gulf Coast, and in Hawaii – although it has been found as far north as Washington in hot weather. The Asian tiger mosquito,
Aedes albopictus
, is also known to transmit the virus, but it is not clear how efficiently. That mosquito ranges as far north as New York and Chicago in summer. Although the virus is normally spread by mosquitoes, there has been one report of possible spread through blood transfusion and one of possible spread through sex. The virus was found on one occasion in semen.
How does Zika cause brain damage in infants?
Experts are only beginning to figure it out. Scientists do not fully understand the connection. The possibility that the Zika virus causes microcephaly – unusually small heads and damaged brains – emerged in October, when doctors in northern Brazil noticed a surge in babies with the condition. It may be that other factors, such as simultaneous infection with other viruses, are contributing to the rise; investigators may even find that Zika virus is not the main cause, although right now circumstantial evidence strongly suggests that it is.
It is not known how common microcephaly has become in Brazil’s outbreak. About three million babies are born in Brazil each year. Normally, about 150 cases of microcephaly are reported, and Brazil says it is investigating nearly 4,000 cases.
What countries should pregnant women avoid?
On Thursday, the Department of Foreign Affairs published
[ new travel adviceOpens in new window ]
for 20 countries over the Zika virus. They are: Barbados; Bolivia; Brazil; Colombia; Dominican Republic; Ecuador; French Guiana; Guadeloupe; Guatemala; Guyana; Haiti; El Salvador; Honduras; Martinique; Mexico; Panama; Paraguay; Suriname; US (Puerto Rico and US Virgin Islands); and Venezuela.
The HSE has an advice sheet at http://www.hpsc.ie/A-Z/Vectorborne/Zika/.
In the US, the Pan American Health Organization believes that the virus will spread locally in every country in the Americas except Canada and Chile.
Have there been cases of Zika in Europe?
Five people in Portugal have tested positive for the virus after recent trips to Brazil, but none required admission to hospital, according to Portugal’s national health institute on Thursday. Also on Thursday, Danish hospital officials said a Danish tourist had been infected by the Zika virus after visiting southern and central America. Romit Jain, from the ECDC in Stockholm, Sweden, said there have been confirmed cases of imported Zika virus infections in Germany and Britain. Zika is not a notifiable disease in the European Union, meaning that EU countries are not required to report cases to the ECDC. Therefore, there is wide variation on reporting by member states.
How do I know if I’ve been infected? Is there a test?
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 hospitalised.
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.
I’m pregnant and I recently visited a country with Zika virus. What do I do?
On January 21st, the European Centre for Disease Surveillance and Control (ECDC) issued an updated risk assessment for the Zika virus, which you can find
. It says that pregnant women who have travelled to areas with Zika virus transmission should mention their travel during antenatal visits in order to be assessed and monitored appropriately.
Does it matter when in her pregnancy a woman is infected with Zika virus?
Earlier in pregnancy seems to be more dangerous. The most dangerous time is thought to be during the first trimester – when some women do not realise they are pregnant. Experts do not know how the virus enters the placenta and damages the growing brain of the fetus. Closely related viruses, including yellow fever, dengue and West Nile, do not normally do so. Viruses from other families, including rubella (German measles) and cytomegalovirus, sometimes do.
Is there a treatment?
No. The US Centers for Disease Control and Prevention does not recommend a particular antiviral medication for people infected with the Zika virus. The symptoms are mild – when they appear at all – and usually require only rest, nourishment and other supportive care.
Is there a vaccine? How should people protect themselves?
Protection is difficult in mosquito-infested regions. There is no vaccine against the Zika virus. Efforts to make one have just begun, and creating and testing a vaccine normally takes years and costs hundreds of millions of euro.
According to the European Centre for Disease Surveillance and Control, travellers to affected areas should take individual protective measures to prevent mosquito bites. This include: using mosquito repellents; wearing long-sleeved shirts and long trousers, especially during the hours of highest mosquito activity; and using mosquito nets if accommodation is not adequately screened or air-conditioned.
If the Zika virus has been in Africa and Asia for decades, why wasn’t the microcephaly problem detected earlier?
Until now, the virus never struck such a large population without immunity. Microcephaly is rare, and it has many other causes, including infection of the fetus with rubella (German measles), cytomegalovirus or toxoplasmosis (cat-litter disease); poisoning of the foetus by alcohol, mercury or radiation; or severe maternal malnutrition and diabetes. It is also caused by several gene mutations, including Down syndrome.
Until recently, health officials paid little attention to Zika virus. It circulated in the same regions as dengue and chikungunya, and compared to those two painful infections Zika was usually mild. The virus is thought to have reached Asia from Africa at least 50 years ago. While it may have caused spikes in microcephaly as it first spread, there was no testing to pin down which of many possible causes was to blame.
In 2007, a Southeast Asian strain of the Zika virus began leap-frogging the South Pacific, sparking rapid outbreaks on islands where no one had immunity to it. Because island populations are small, rare side effects did not occur often enough to be noticed. But in 2013, during an outbreak in French Polynesia, which has 270,000 residents, doctors confirmed 42 cases of Guillain-Barré syndrome, which can cause paralysis. That was about eight times the normal number and the first hint that Zika virus can attack the nervous system, which includes the brain.
Zika was first confirmed in Brazil – a country of 200 million – last May, and it spread like wildfire. The first alarms about microcephaly were raised only in October, when doctors in the northeastern state of Pernambuco reported a surge in babies born with it. Pernambuco has nine million people and 129,000 annual births. In a typical year, nine are microcephalic infants. By November 2015, when Brazil declared a health emergency, Pernambuco had had 646 such births.
New York Times and additional reporting