A baby with microcephaly (left) compared to a baby with a typical head size. Scientists think Zika fever causes microcephaly in fetuses
**Zika fever** is an illness caused by the Zika virus. The Zika virus belongs to the genus *Flavivirus*, like dengue fever and chikungunya. However, Zika fever is usually not as bad as those illnesses. Most people who get the Zika virus (60-80%) have no symptoms.

People who do have symptoms usually have a low fever, conjunctivitis, joint pain (mainly in the hands and feet), and a rash. The rash often starts on the face and then spreads to the rest of the body. Usually, the symptoms are not very bad, and get better after 2 to 7 days.

Starting in 2015, there has been an outbreak of Zika virus (meaning that many people have gotten the virus) in Brazil. Scientists think that when a woman with the Zika virus is pregnant, she can give the virus to her fetus. Scientists think this can cause microcephaly, a birth defect that causes a baby to have a smaller head than usual. This can cause intellectual disability and other problems in the brain, like seizures. Because of this, in January 2016, the United States Centers for Disease Control and Prevention warned pregnant women not to travel to Brazil, Colombia, El Salvador, French Guiana, Guatemala, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Suriname, Venezuela, or Puerto Rico, because of the risk of getting the Zika virus there.

In places where the Zika virus lives, people are more likely to have birth defects, neurological problems like Guillain-Barré syndrome, and autoimmune diseases.

Diagnosis
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Diagnosing Zika fever is difficult for a few reasons. First, Zika fever causes many of the same signs and symptoms as many other viruses.

Second, special laboratory tests have to be done to prove that a person has Zika virus. For example, when the virus is in a person's blood or urine, it can be found by using a special test that looks for the virus's RNA in the blood. However, the Zika virus often does not stay in the blood for very long. Also, because most people with the Zika virus have no symptoms, they do not know that they need to be tested. Blood tests that look for specific antibodies (which the body sends out to fight the Zika virus) can also be done. However, these tests are expensive and have to be done in special laboratories that do not exist everywhere.

If tests cannot prove that a person has Zika virus, it can be difficult to figure out whether a person has Zika fever or a different infection. The United States Centers for Disease Control and Prevention (CDC) says that before doctors diagnose a person with Zika fever, they should think about whether the person could have one of many other infections. Examples of these infections include:

* Dengue fever
* West Nile virus
* Chikungunya
* Malaria
* Rubella
* Measles
* Leptospirosis

Transmission
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Humans get the Zika virus after being bitten by mosquitoes from the *Aedes* genus. Scientists have proven that at least eight different species of mosquitoes from the *Aedes* genus can spread the Zika virus to humans. Mosquitoes pick up the Zika virus after they bite other animals that have the virus.

Zika virus can be passed from one person to another during sexual intercourse. It can also be passed from a mother to her fetus during pregnancy.

Prevention
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Protecting against mosquitoes - like by using a mosquito net while sleeping - is the best way to avoid getting the Zika virus
There is no vaccine for Zika virus, though the United States National Institutes of Health is trying to make one.

The best way for a person to protect themselves against the Zika virus is to protect themselves against mosquitoes. For example, if people are traveling to places where the Zika virus lives, they should:

* Wear long-sleeved shirts and long pants
* Use bug spray
* Stay and sleep in rooms that are protected by window and door screens, and that have air conditioning (if possible)
* Use a mosquito net when sleeping

Treatment
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Today, there is no treatment or cure for Zika fever. Medical professionals can only give "supportive care," which means they can only treat the virus's symptoms. For example, they can give medicines to help with pain, fever, and itching. However, some scientists say that doctors should not give medicines like aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs), which are commonly used for pain and fever. This is because people with similar viruses who take these medicines have been more likely to have bleeding problems.

There are no known anti-viral medications (medicines which kill viruses) which will kill the Zika virus.

Because there are no treatments that will cure the Zika virus once a person has it, scientists suggest that pregnant women do everything they can to avoid getting the virus. Once a pregnant woman has the Zika virus, there is nothing anyone can do to keep her fetus from getting infected too.

Epidemiology
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Zika fever was first discovered in 1947, in a rhesus monkey in the Zika Forest in Uganda. The first human cases were reported in Nigeria in 1954. A few outbreaks have been reported in tropical Africa and in some parts of Southeast Asia, but not India. In 1977–1978, Zika virus caused fevers in Indonesia.

Countries where people have gotten Zika virus (as of January 2016)
The first major outbreak happened in 2007 in Micronesia's Yap Islands. 185 people were proven to have the Zika virus. This was the first time Zika fever had been reported outside Africa and Asia. In 2013, another large outbreak happened in French Polynesia.

In May 2015, Brazil officially reported its first 16 cases of Zika fever. By November 2015, Zika fever had appeared in 14 states in Brazil. Zika virus is thought to have caused 2,400 cases of microcephaly and 29 infant deaths in Brazil in 2015.

Since first appearing in the Western Hemisphere in February 2014, Zika fever has spread quickly throughout South America and Central America. It appeared in Mexico in November 2015.

On January 24, 2016, the World Health Organization warned that the Zika virus is likely to spread to nearly all countries of the Americas. This is likely since the mosquito that spreads the virus, *Aedes aegypti*, lives in all of the countries in the Americas, except for Canada and Chile.

On February 1, 2016, the World Health Organization said that the Zika virus was a "public health emergency." They also said the Zika virus was "spreading explosively" (very quickly), and that in the next year, as many as 3 million to 4 million people could get the virus.

Related pages
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* *Flaviviruses*
* *Aedes* genus of mosquitoes
	+ *Aedes agypti*
* Infectious disease