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Zika Virus: Still of Concern?

Medically reviewed by Carmen Fookes, BPharm. Last updated on Nov 11, 2021.

The Lowdown - What is Zika?

Zika is a viral infection caused by the Zika virus. This virus is more commonly spread through the bite of an infected Aedes mosquito.

The first reported cases of Zika in humans were detected in the 1950s and in more recent years outbreaks have been reported in tropical Africa, Southeast Asia, and the Pacific Islands. Before 2014, very few travel-related cases of Zika were reported in the United States. That changed during 2015 and 2016 when large outbreaks of the Zika virus occurred in the Americas.

During 2015, Zika was not a notifiable disease in the U.S.; however, 62 cases in travelers returning from affected areas were reported to Arbonet, a national arboviral surveillance system managed by the CDC.

In 2016, the number of travelers returning with Zika skyrocketed to 4897. Florida and Texas were the only U.S. states to report locally acquired infection, with 218 people infected in Florida and 6 in Texas.

The number of Zika infections plummeted in 2017, with previous hot spots like Brazil reporting dramatic declines in rates. 452 symptomatic cases of Zika were identified in the U.S. during 2017, with 437 of those occurring in travelers returning from affected areas. 7 cases were locally acquired and 8 were acquired through other routes, such as sexual or laboratory transmission. But since 2018, no local Zika transmission has been reported in the continental United States; and less than 100 travelers have acquired the disease.

In 2021, only 1 traveler contracted Zika and there have been no confirmed cases of Zika using molecular testing from the U.S. territories.

Zika seems to have gone quiet, but although there are no current outbreaks worldwide, there is still a risk of being infected with Zika, because the virus is still present in more than 90 countries.

Zika, just like other epidemic-prone pathogens (such as dengue and chikungunya), is prone to an "ebb and flow" wave style of infection. Before traveling internationally, check out which countries have Zika as a risk.

How Is Zika Spread?

Most Zika infections are transmitted via mosquito bites, particularly from the day-time-active, Aedes species of mosquito. The mosquito bites an already infected human, then bites an uninfected person, transmitting the virus to them. Monkeys can also harbor the virus. The Aedes species of mosquito is also responsible for the transmission of other viral illnesses, such as Dengue fever and Chikungunya.

Most populations of the more common Culex mosquito do not appear capable of spreading the Zika virus; however, one type, Cx quinquefasciatus, is.

Zika can also be spread sexually through semen and possibly oral sex, and via infected blood transfusions. Pregnant women infected with the virus can pass it onto their unborn child via the placenta. It does appear that the Zika virus can survive on hard surfaces, such as bench tops and door handles, for up to eight hours; however, common household disinfectants are highly effective at killing Zika.

What Are The Symptoms?

Four out of five people infected with Zika experience no symptoms, or barely noticeable symptoms. One out of five people develops "Zika Fever", symptoms of which include a low-grade fever, headache, a facial rash that rapidly spreads over the whole body, joint and muscle pain, and conjunctivitis (red eyes). Abdominal pain, tiredness, nausea, or vomiting may also be reported. Symptoms usually arise within 10 days of a bite from an infected mosquito and recovery usually takes a week. Hospitalization because of the disease is uncommon.

Infection with Zika has been associated with Guillain-Barré syndrome - an autoimmune nerve disorder that causes rapid-onset of muscle weakness and paralysis - in adults testing positive for the virus. Zika can also cause uveitis, an inflammation of the eye, which may progress to cataracts and increased eye pressure if left untreated. A case of sensory polyneuropathy tied to Zika infection has also been reported in an elderly man.

But perhaps the most worrying thing about Zika is how it affects the unborn babies of pregnant women. Research shows 5%-14% give birth to children with signs of congenital Zika syndrome (which affects how an infant's brain and eyesight develops), and a 4%-6% subset have children with microcephaly (small head, incomplete brain development).

The good news is that fewer babies than previously thought are affected by the virus. The bad news is that some children born asymptomatic can develop Zika-related problems later on.

How Is Zika Diagnosed?

Blood or urine tests can help confirm Zika infection; however, few laboratories offer Zika testing and it is not considered necessary unless you are showing signs of Zika AND you have traveled to a country with a current Zika outbreak.

Rapid virological PCR tests used 3-5 days after the onset of symptoms can help distinguish Zika from other viral infections. Other tests look for the presence of antibodies. Testing may take two to four weeks depending on a laboratory's workload. During a widespread outbreak, most people will be diagnosed clinically, based on their symptoms and recent history (for example, the virus is known to be circulating in the area).

When the outbreak happened in 2016 in Brazil, the diagnosis of Zika was initially challenging because of the similar way the disease presents to Dengue fever and Chikungunya. Looking back, an outbreak of disease attributed to Dengue fever in Brazil in early 2015 may have actually included a number of Zika virus infections, meaning the disease was probably rampant earlier than previously thought.

What Countries Are At Risk Of Zika?

More than 90 countries currently have some risk of Zika. How likely you are to catch it depends on exactly what country you are going to, where you are staying, how you are traveling around, and what partners you choose to have sex with.

If you are already pregnant or if there is a chance that you might become pregnant while you are away, then you are best to avoid those countries until after the baby is born. If you must travel, then you should strictly follow all advice recommended to avoid mosquito bites and prevent sexual transmission of the virus. At least 116 cases of birth defects and nine deaths in newborns attributable to Zika have been reported to the CDC.

Why Did An Outbreak Occur in 2016?

Although small and relatively minor outbreaks of Zika had previously been reported in tropical regions, the outbreak that occurred in Brazil in 2016 was unprecedented. Why?

Global trade and travel has significantly contributed to the explosive spread of the Aedes species of mosquito, such that it is now present in every continent, including North America. As a result of climate change, the world is also becoming warmer and wetter - the perfect breeding ground for all types of mosquitoes.

2016 also saw an unprecendented number of Dengue fever cases reported, with that mosquito-borne disease now endemic in more than 100 countries, up from nine in the 1970s. Although numbers dropped in 2017-18, a sharp increase in Dengue cases was reported in 2019.

Treatment For Zika

Unfortunately, there is no specific medicine or vaccine available to treat Zika, although several vaccines are or have been in development, experts are unsure if one will ever make it to market. The best way to recover from the illness is to get plenty of rest, drink fluids to prevent dehydration, and to take acetaminophen to relieve pain.

Aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs) are not recommended until Dengue Fever has been ruled out to reduce the risk of bleeding.

Most people recover from the illness within a week; however, uncommonly some people develop Guillain-Barré syndrome, uveitis, and some babies born to women infected with Zika are born with microcephaly, or other birth defects, such as hearing loss.

People with Zika virus infection should be careful to avoid mosquito bites and be aware that the virus can be passed on through sex (including vaginal, anal, and oral sex and the sharing of sex toys). Zika can remain in semen for at least three months. Condoms should be used (although these are not 100% effective at preventing transmission of the virus) or couples should abstain from sex for at least three months.

All blood that is donated in the U.S. is now screened for the Zika virus.

How Can I Avoid Getting Zika?

The same precautions recommended to protect against Dengue and Chikungunya also protect against Zika.

Eliminating or controlling mosquito breeding grounds is the most effective way to control the virus. Any container or natural depression that collects water - even as little as a teaspoonful - can become a breeding ground for mosquitoes, including water tanks, old tires, discarded tin cans, gutters and flat roofs. Water receptacles for drinking should be covered with a lid and other stagnant areas sprayed. Consider introducing larvivorous fish, such as guppies, to ornamental water features as these eat mosquito larvae.

Protect yourself from mosquito bites, even during the day by wearing long sleeves and pants, installing insect screens to windows and doors, sleeping under mosquito nets and using an insect repellent such as DEET or picaridin.

Advice Pertinent To Pregnant Women

If you are pregnant and plan to travel, always check on the CDC website to establish the Zika status of the country you intend to go to. Seriously consider postponing your trip until after you have the baby if that country carries a serious risk of Zika. The first two trimesters of pregnancy seem to be the most dangerous time for the unborn baby to be exposed to the virus; however, Zika can still cause lesions in the brains of unborn babies right up until birth. No matter which trimester you are in, it is best to save your trip for another time.

If travel to a Zika-infected country is unavoidable, then take the utmost precautions to protect yourself from mosquito bites. Since the virus is often symptomless and microcephaly may be difficult to detect on ultrasound, you may not realize you have been exposed to the virus until after your baby is born.

If you are pregnant and your partner has traveled to an area with Zika, then the CDC recommend you use barrier contraceptive methods or abstain from sex for the rest of your pregnancy, regardless of whether your partner has symptoms or not. In most men, the Zika virus lingers in semen for no longer than three months; however, it may be best to err on the side of caution and delay pregnancy for at least six months if your partner has recently traveled to a Zika-infected area.

Finished: Zika Virus: Still of Concern?

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