Zika Virus
The World Health Organization [ The World Health Organization is a specialized agency of the United Nations that is concerned with international public health. It was established on 7 April 1948, headquartered in Geneva, Switzerland. ] has declared the Zika virus, an international public health emergency, prompted by growing concern that it could cause birth defects. As many as four million people could be infected by the end of the year.
The infection appears to be linked to the development of unusually small heads and brain damage in newborns – called microcephaly – as well as other neurological defects. In adults, the virus is linked to a form of temporary paralysis.
Here are some answers and advice about the outbreak.
1. 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 May, when an outbreak occurred in Brazil.
Until now, almost no one on this side of the world had been infected. Few people here have immune defenses against the virus, so it is spreading rapidly. Millions of people in tropical regions of the Americas may now have been infected.
Yet for most, the infection causes no symptoms and leads to no lasting harm. Scientific concern is focused on women who become infected while pregnant and those who develop a temporary form of paralysis after exposure to the virus.
2. How does a mosquito transmit Zika?
The virus moves from its gut to its salivary glands.
Only female mosquitoes bite people: they need blood to lay eggs. They pick up the virus in the blood. It travels from their gut through their circulatory system to their salivary glands and is injected into its next human victim. Mosquito saliva contains proteins that keeps blood from clotting. When a mosquito bites, it first injects saliva so its prey’s blood does not clog its strawlike proboscis.
3. What areas is Zika likely to reach?
Wherever certain mosquitoes go.
Zika is spread by mosquitoes of the Aedes genus, 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, D.C., 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.
4. Can the Zika virus be sexually transmitted?
Yes.
Experts believe that the vast majority of Zika infections are transmitted by mosquitoes, not sex.
As of early March, however, more than a more than a dozen instances of transmission through sex have been reported in four countries.
In each case in which details were released, the virus was transmitted by a man who had visited a region where the infection circulates to a woman who had not.
Live virus has been found in semen more than two months after symptoms of infection disappeared. Scientists believe the prostate or testes can serve as a reservoir, sheltering the Zika virus from the immune system. In some cases, the men with infections had blood in their semen.
Health authorities now recommend that women who are pregnant or trying to become pregnant avoid contact with semen from men who have visited areas where the Zika virus is transmitted. Women who are pregnant should have sex only with partners using a condom, or abstain, until they give birth – whether they are engaging in vaginal, anal or oral sex.
There are still many unknowns.
Can a woman pass the virus to a man through sex? Can it be passed through anal, oral or other forms of sexual contact?
Does a man have to have blood in his semen to be infectious? Is he infectious before the blood appears?
If there is no blood, must he have had symptoms of Zika infection, like fever and rash, to be contagious? How long does a man remain infectious?
5. How might Zika cause brain damage in infants?
Experts aren’t yet certain.
The possibility that the Zika virus causes microcephaly – unusually small heads and often damaged brains – emerged in October when doctors in northern Brazil noticed a surge in babies with the condition.
Several reports now have shown that the virus can cross the placenta and attack fetal nerve cells, including some that develop into the brain.
Studies to prove whether the virus was to blame for microcephaly are expected to take until June, but evidence continues to mount. The virus is now considered “guilty until proven innocent,” one World Health Organization official said.
Normally, microcephaly occurs in about 1 in 5,000 to 1 in 10,000 of all births. Scientists analyzing outbreaks of the Zika virus in French Polynesia and northeast Brazil have estimated that the incidence rose to nearly 1 in 100 births nine months after those outbreaks peaked.
6. What is microcephaly?
An usually small head, often accompanied by brain damage.
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 Dr. Constantine Stratakis, a pediatric geneticist and a scientific director at the National Institute of Child Health and Human Development.
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 develop a range of problems, like developmental delays, intellectual deficits or hearing loss.
The consequences can vary widely. Pinpointing an underlying cause helps clinicians to advise parents about their newborn’s prognosis.
Genetic abnormalities are a common cause. Microcephaly can also be caused by infections of the fetus, including German measles (also known as rubella), toxoplasmosis (a disease caused by a parasite found in undercooked contaminated meat and cat feces) and cytomegalovirus.
Microcephaly may also result if a pregnant woman consumes alcohol, is severely malnourished or has diabetes. If the defect occurs in a child’s first years, it may be a result of a brain injury during labor.
There is no treatment for an unusually small head.
“There is no way to fix the problem, just therapies to deal with the downstream consequences,” said Dr. Hannah M. Tully, a neurologist at Seattle Children’s Hospital who specializes in brain malformations.
7. What places should pregnant women avoid?
More than 30 countries and territories, mostly in the Americas and South Pacific.
World health authorities expect the outbreak to eventually reach every place in the Americas where the Aedes aegypti mosquito has previously spread the dengue virus. That includes everywhere from South Florida and the Gulf Coast to northern Argentina and Chile. Hawaii will be affected as well; some Pacific Islands are now having outbreaks.
Even within those countries, according to the C.D.C., pregnant women can safely visit areas at altitudes above 6,500 feet because mosquitoes are not normally found there. The latest C.D.C. updates are here.
8. 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 hospitalized.
There is no widely available test for Zika. Because it is closely related to dengue and yellow fever, it may cross-react with antibody tests for those viruses. To detect the virus, 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.
9. I’m pregnant and live in or recently visited a country with Zika virus. What do I do?
Pregnant women should get blood tests and ultrasound scans.
The C.D.C. has updated its guidelines several times.
As of early March, all pregnant women who have visited areas with active Zika transmission should have a blood test for the virus, whether or not they have symptoms.
All pregnant women who live in those areas, such as Puerto Rico or American Samoa, should be tested at least twice during their pregnancies, whether or not they have symptoms.
Testing for the virus is highly accurate in the first week after symptoms appear. After that, diagnostic tests must rely on antibodies, and false positives are possible if a woman has been infected with related viruses, like dengue and yellow fever, or has been vaccinated against them.
More complex testing can lower the false-positive rate, but not eliminate it.
In addition, all pregnant women who may have been exposed should have at least one ultrasound looking for evidence of fetal microcephaly or calcifications, indicating that the fetal skull is hardening too early.
If tests show that a woman is infected, she should have ultrasounds at regular intervals.
Unfortunately, ultrasounds usually cannot detect microcephaly before the end of the second trimester.
10. I’m of childbearing age, but not pregnant and not planning to get pregnant. Should I go to an affected country?
Only if you use birth control consistently.
Half of pregnancies are unintended. If you want to visit a country where Zika transmission has been reported, Dr. Laura E. Riley, a specialist who works with high-risk pregnancies and infectious disease at Massachusetts General Hospital, advises strict use of birth control to ensure you don’t become pregnant.
Women who become unexpectedly pregnant while traveling or shortly afterward will have to deal with blood tests, regular ultrasounds and a great deal of anxiety.
“Why would you ever sign yourself up for that?” Dr. Riley said. “There’s enough in life to worry about. I wouldn’t add that to my list.”
11. I’m pregnant now, but wasn’t when I visited one of the affected countries. What’s the risk?
Very low.
With rare exceptions, the virus does not appear to linger in women, and those who recover from the infection are immune.
“Our understanding thus far is that the risk is very, very low if you were in that place prior to conception,” Dr. Laura E. Riley of Massachusetts General Hospital said.
“I wouldn’t be worried about if you conceived after you got back to the U.S.”
12. If I live in an area where the virus is circulating, should I delay becoming pregnant?
That may be wise, some officials say.
Health officials in five countries — Brazil, Colombia, Ecuador, El Salvador and Haiti — and Puerto Rico have suggested that women delay pregnancy temporarily. Obstetricians in some countries are privately giving patients the same advice, saying the risk of fetal damage during an epidemic’s peak is too great.
Once infected residents have recovered and have become immune, these officials argue, the epidemic will fade and women can safely become pregnant again. Also, many companies are working on Zika vaccines, and delaying pregnancy will buy time for them to arrive.
The Centers for Disease Control and Prevention recently recommended that women who have had symptoms of the virus or tested positive for it should wait at least eight weeks after their symptoms first appeared before trying to get pregnant.
Officials recommended that men who had symptoms should wait six months before having unprotected sex. The virus has been known to live longer in semen. Symptoms can include rashes and sore joints.
13. Does it matter when in her pregnancy a woman is infected with the Zika virus?
Anytime during pregnancy may be dangerous.
Originally, doctors in Brazil believed that infections in the first trimester were the most dangerous, because mothers who gave birth to babies with microcephaly were usually infected then.
A later study found that some mothers infected late in pregnancy also had disastrous outcomes, including the sudden deaths of infants in the womb.
Some experts who have studied the long-term consequences of rubella – another virus that attacks fetuses – say they believe that children who survive a Zika infection without microcephaly nonetheless may suffer serious consequences, including blindness and deafness at birth, learning and behavior difficulties in childhood, and perhaps even mental disabilities later in life.
14. Should infants be tested?
Other birth defects may be linked to the virus.
Federal health officials say that newborns should be tested for infection with the Zika virus if their mothers have visited or lived in any country experiencing an outbreak and if the mothers’ own tests are positive or inconclusive.
The reason, officials said in interviews, is that infection with the virus could be linked to defects in vision and hearing, among other abnormalities, even if the child does not suffer microcephaly. The other defects may require further assessments and testing.
15. I’m a man and have returned from a place where the Zika virus is spreading. How long until I can be sure that I won’t infect a sexual partner?
Err on the side of caution.
Whether or not you have had symptoms, you should do everything you can to avoid infecting a woman who may be pregnant or is trying to become pregnant, because the consequences for the baby may be disastrous.
To do that, you must avoid vaginal, anal and oral sex for the length of the pregnancy — or use condoms every time.
It is not known how long the Zika virus can survive in semen, but live virus has been found in men more than two months after infection. The testes are somewhat shielded from the immune system, so it may take longer for the body to eliminate an infection there.
The Centers for Disease Control and Prevention recently recommended that men and women who have traveled to Zika-infected areas, but had no active signs of the disease, wait eight weeks before trying to get pregnant “in order to minimize risk.”
Men who have had symptoms of Zika infection, on the other hand, should wait six months before having unprotected sex, officials said. Symptoms can include rashes and sore joints.
It is not known whether men must develop symptoms to be infectious, or whether men must have blood in their semen to be infectious.
It is not known whether a gay man can infect a male partner through sex, but it is theoretically possible, doctors say.
16. Is there a treatment?
No.
The C.D.C. 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.
Health workers sprayed insecticide in the Sambadrome in Rio de Janeiro as part of a campaign to combat mosquitoes, which transmit the Zika virus.
17. 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 dollars.
Because it is impossible to completely prevent mosquito bites, the C.D.C. has advised pregnant women to avoid going to regions where the virus is being transmitted, and has advised women thinking of becoming pregnant to consult doctors before going.
Travelers to these countries are advised to avoid or minimize mosquito bites by staying in screened or air-conditioned rooms or sleeping under mosquito nets; wearing insect repellent at all times; and wearing long pants, long sleeves, shoes and hats.
source-By DONALD G. McNEIL Jr., CATHERINE SAINT LOUIS and NICHOLAS ST. FLEUR