What You Need to Know About Zika Virus Disease

On February 1, 2016, the World Health Organization (WHO) declared the spread of Zika virus a Public Health Emergency of International Concern (PHEIC), an official designation that indicated a high level of concern about the rapid spread of the virus. The WHO declaration, followed a May 1 alert from the Pan American Health Organization (PAHO) about the spread of Zika virus in Brazil – and a simultaneous increase in babies born with birth defects.

What is Zika virus disease? How concerned should you be about it? What can you do to protect yourself and your family? Here are the things you need to know about Zika virus disease and the current epidemic.

What is Zika Virus Disease?

Zika virus disease is a disease caused by infection with a virus called – unsurprisingly — Zika. The virus spreads mostly when people are bitten by an infected Aedes species mosquito. The virus is a member of the flaviviridae family and is related to other flaviviruses carried by mosquitoes, including dengue, West Nile, and Japanese encephalitis viruses.

Zika virus was first isolated in 1947 from a rhesus monkey that was being used for research on jungle yellow fever. The first human cases of Zika virus disease were reported in 1952 in Uganda and the United Republic of Tanzania. Since then, outbreaks of Zika virus disease have been reported in tropical Africa, Asia, and the Pacific Islands. The current outbreak is the first in the Americas, and there is concern that it will spread throughout Americas and Europe.

What is a PHEIC?

A PHEIC is defined in the International Health Regulations as “an extraordinary event which is determined to constitute a public health risk to other States through the international spread of disease and to potentially require a coordinated international response.”

The WHO’s action in declaring a PHEIC was a call to governments around the world to invest in preventing a rapidly spreading disease from potentially devastating effects. On February 22, U.S. President Barak Obama called on Congress to approve used of $1.9 billion (some of which was left from emergency funding to fight the Ebola outbreak in 2015). While the U.S. request was by far the largest, other countries followed suit. The European Union pledged €10m, while the U.K. contributed £1 million [$1.46 million] to the effort.

What are the Signs and Symptoms of Zika Virus Infection?

Zika virus infection generally causes mild disease. Symptoms, which last from two to seven days, include fever, skin rashes, conjunctivitis, muscle and joint pain, malaise, and headache. While the incubation period is not known, it is thought to be a few days.

While most people affected by Zika virus experience only mild – and in many cases, no – symptoms, the disease can also have severe consequences, especially in people with immune disorders or severe chronic illness.  

Problems with the immune system and nervous system may develop after infection with Zika virus. A team of French scientists reported that the risk of Guillain-Barré syndrome (GBS) – a rare disorder in which the body’s immune system attacks part of the nervous system, causing partial paralysis – was dramatically higher for people who had been infected with Zika virus. After a Zika outbreak in French Polynesia, 42 people were diagnosed with GBS, all of whom had experienced Zika disease. In contrast, during a typical year, between 3 and 10 cases of GBS would have usually been expected to occur.

How is Zika Virus Diagnosed?

Diagnosis of Zika virus is based on symptoms, history, and laboratory tests. History includes travel to an affected region, sexual relations with a person who has or is at risk of infection, and, in the case of an infant, a mother who is at risk or showing signs of infection.

A blood test can confirm whether a person is actively infected or has been infected with the virus. Using just a small sample of blood taken from the person’s arm, the laboratory can detect Zika virus, viral RNA, or viral antigen; or Zika virus immunoglobulin M (IgM) antibodies. Testing is available through the CDC and in some state health departments.

How Does Zika Virus Spread?

Zika virus is a vector-borne disease, meaning it spreads mostly via the bite of an infected Aedes species mosquito (the “vector”). The primary carrier of Zika virus is the Aedes aegypti mosquito, which lives in tropical and subtropical regions. The Aedes aegypti mosquito does not survive in cooler temperatures. Another mosquito species – Aedes albopictus – has also been identified as a vector for Zika virus. Unlike its tropical cousin, the Aedes albopictus mosquito can hibernate and survive in cooler temperatures.

Like other vector-borne diseases such as dengue, malaria, and West Nile, the wide and growing range of mosquitoes makes it difficult to control. While mosquitoes are the primary vector for the spread of Zika virus, there’s growing concern about human-to-human transmission of the virus. Human-to-human transmission appears to be possible with sexual activity; pregnant women may also transmit the virus to their fetuses. It is not known whether the virus can be spread through blood transfusions or breastmilk, but officials are recommending caution.

According to the U.S. Centers for Disease Control (CDC), three cases suggest that sexual transmission of Zika virus is possible. In the first case, a man appears to have transmitted the disease to his female sex partner; sexual contact occurred before the man showed any symptoms of the disease. A second case is under investigation by the Dallas County Health and Human Services department. In the third case, researchers isolated Zika virus from the semen of an infected man up to 10 weeks after he had first shown signs of the disease.

In all three cases, the men showed symptoms of Zika infection. Researchers do not know whether infected men who never develop symptoms can transmit Zika virus to their sex partners. Sexual transmission of Zika virus from infected women to their sex partners has not been reported.

Evidence suggests that pregnant women can pass the virus to their fetuses – often with devastating consequences. Infection with Zika virus has been linked to birth defects, especially microcephaly, a condition in which babies are born with small heads and underdeveloped brains. In infants with microcephaly, the head may head stop growing after birth. Convulsions are common in Infants born with microcephaly, as are physical and learning disabilities during development. Microcephaly can range from mild to severe. Zika virus infection in pregnant women has also been associated with miscarriage (spontaneous abortion) and other severe birth defects.

While researchers are still exploring the connection between Zika virus and microcephaly, evidence suggests that Zika infection may indeed cause central nervous system birth defects including microcephaly in infants:

• Epidemiological data from affected areas on Brazil suggest a strong association: During the first 11 months of 2015, almost 1,300 suspected cases of microcephaly were reported throughout Brazil, a rate nearly 8 times that of a typical year, during which 150 to 200 children would be born with microcephaly. In the 14 Brazilian states most affected by Zika virus, epidemiological data showed a 20-fold increase in microcephaly among newborns.
• After an outbreak of Zika virus in French Polynesia, 18 infants were born with central nervous system defects – including nine with microcephaly. In comparison, the usual average was zero to two cases per year.

There’s another challenge in controlling Zika virus: In 80% of cases, people infected with Zika virus show no signs or symptoms. When symptoms do appear, they may be mistaken for symptoms of other more common illnesses, such as a cold or flu. Although the risk of sexual transmission is not well understood, it is possible that people who do not know they are infected may infect others through sexual contact.

What Countries are affected by Zika Virus?

On March 1, 2016, the WHO reported that between January 2007 and February 25, 2016, 52 countries and territories had reported local transmission of Zika virus. The primary spread occurred in parts of Asia, much of South and Central America, and islands in the Caribbean. Since first being reported in the Americas in 2015, the virus has spread to 31 countries in the region. Most recently, Marshall Islands, Saint Vincent and the Grenadines, and Trinidad and Tobago reported local transmission of Zika virus.

The CDC recommends that travelers check its travel notice website frequently, as the Zika virus continues to spread rapidly, and it is impossible to predict how or where it will spread.

What is the Treatment for Zika Virus Disease?

There is no specific treatment for Zika virus infection. Experts recommend supportive care:

• Get plenty of rest
• Drink extra fluids to prevent dehydration.
• Take acetaminophen (Tylenol) for fever and pain.
• Do not take aspirin, ibuprofen (Motrin), naproxen (Aleeve), or other nonsteroidal anti-inflammatory drugs.
• If you are taking medicine for another medical condition, consult your health-care provider.
• Consult your health-care provider if you experience any symptoms of GBS, including partial paralysis, numbness, tingling, 

How can I prevent Zika Virus disease?

There is currently no vaccine or medication that can prevent Zika virus infection. The WHO and U.S. CDC recommend that all people living in or traveling to areas of ongoing Zika virus transmission take the following precautions:

• Prevent mosquito bites:
  • Use insect repellent on exposed skin and clothing, as directed on the label. The WHO recommends using a repellent that contains DEET. Repellents are considered safe for use by pregnant women.
  • Wear light-colored clothes that cover as much of the body as possible, including long pants, long-sleeve shirts, socks, and hats.
  • Lock mosquitos out using physical barriers including screens and closing doors and windows
  • Sleep under mosquito nets.
• Practice safer sex – or refrain from sex:
  • Men who have been infected should use condoms or refrain from sexual activity, especially if their partners are pregnant. At this time, routine testing of men who have been in high-risk areas is not recommended.
  • Women who live in or travel to areas where Zika virus has been reported should discuss the risks of becoming pregnant with their health-care providers; women who do not wish to become pregnant should use contraceptive methods to prevent unintended pregnancies.
• During pregnancy:
  • If possible, pregnant women should avoid travel to areas where Zika virus has been reported.
  • Pregnant women who live in regions where Zika transmission is occurring should be tested for the virus.
  • Women are at risk throughout their pregnancies. Protection from mosquitoes remains the first and most important line of defense; pregnant women in affected regions should use condoms or refrain from sex.

Reviewed by Dr. Amesh Adalja, Infectious Diseases Society of America

Additional Sources

European Centre for Disease Prevention and Control. (10 December, 2015). Rapid risk assessment: Zika virus epidemic in the Americas: potential association with microcephaly and Guillain-Barré Syndrome. Stockholm: ECDC.

National Institute of Neurological Disorders and Stroke. (2016). Guillain-Barré Syndrome Fact Sheet. http://www.ninds.nih.gov/disorders/gbs/detail_gbs.htm

Oduyebo T, Petersen EE, Rasmussen SA, et al. (2016). Update: Interim Guidelines for Health Care Providers Caring for Pregnant Women and Women of Reproductive Age with Possible Zika Virus Exposure — United States, 2016. MMWR Morb Mortal Wkly Rep. 65:122–127. DOI: http://dx.doi.org/10.15585/mmwr.mm6505e2.

Oster AM, Brooks JT, Stryker JE, Kachur RE, Mead P, Pesik NT, Petersen LR. (12 Feb, 2016) Interim Guidelines for Prevention of Sexual Transmission of Zika Virus – United States, 2016. MMWR Morb Mortal Wkly Rep. 65(5):120-1. http://dx.doi:10.15585/mmwr.mm6505e1.  

World Health Organization. (26 Feb, 2016). Zika Virus, Microcephaly, and Gullain-Barré Syndrome. Situation Report. Retrieved March 1, 2016, from: http://apps.who.int/iris/bitstream/10665/204491/1/zikasitrep_26Feb2016_eng.pdf?ua=1