Zika Virus: Important Questions Answered
Medically reviewed on Nov 3, 2017 by C. Fookes, BPharm.
The Lowdown - What is Zika?
Zika is viral infection caused by the Zika virus. This virus is more commonly spread through the bite of an infected Aedes species mosquito.
The first reported case of Zika in humans occurred in the 1960s in Nigeria. Outbreaks have previously been reported in tropical Africa, Southeast Asia, and the Pacific Islands. Researchers have suggested the Zika virus responsible for the 2016 widespread outbreak stemmed from the Pacific Islands, possibly somewhere between May and December 2013, more than a year before it was first reported in Brazil.
During 2016, Florida and Texas were the only U.S. states to report locally acquired infection, with 218 people infected in Florida and 6 in Texas, although 4830 travel-related cases were reported.
The number of Zika infections plummeted in 2017, with previous hot spots like Brazil reporting dramatic declines in rates, which was good news for U.S. travellers. Up until the end of October 2017, only 326 symptomatic cases of Zika had been reported in the U.S., with only 1 of those presumably locally acquired.
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.
Luckily, the more common and globally prevalent Culex mosquito does not appear capable of spreading the virus.
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 may also be possible to catch the virus through sweat or tears. Spread through saliva or urine has not yet been confirmed. It does appear that the Zika virus can survive on hard surfaces, such as bench tops and door handles, for 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 symptoms that are barely noticeable. One out of five people develop "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.
The biggest concern with Zika virus infection is that outbreaks in Brazil have been associated with a twenty-times higher rate of babies born with microcephaly (small head, incomplete brain development) and intracranial calcifications (calcium deposits in the brain). In addition, an increase in the number of cases of Guillain-Barré syndrome - an autoimmune nerve disorder that causes rapid-onset of muscle weakness and paralysis - have also been reported.
Zika can also cause uveitis, an inflammation of the eye, which if left untreated could cause cataracts and increased eye pressure. A case of sensory polyneuropathy tied to Zika infection has also been reported in an elderly man.
How Is Zika Diagnosed?
Blood tests can help confirm Zika infection; however, few laboratories offer Zika testing. 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. During a widespread outbreak, most people will be diagnosed clinically, based on their symptoms and recent history (ie, known Zika outbreak in their region or recent travel to areas where the virus is circulating).
In Brazil, 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 Have Reported Cases Of Zika?
Locally transmitted Zika virus has been reported in over 50 countries, including Cape Verde, the Caribbean including Jamaica, Central and South America, Mexico, Singapore and the Pacific Islands (American Samoa, Samoa, and Tonga).
Worldwide, almost every country has reported Zika in returning travelers, including pregnant women.
At least 98 cases of birth defects and eight deaths in newborns attributable to Zika had been reported to the CDC as of October, 2017.
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. Statistics already show that Dengue fever infections rose 30-fold from the 1960s to 2013, and several countries have reported record outbreaks in the past five years. International travel and the fact that almost 80% of people carrying the virus are asymptomatic means the virus can be easily spread by people who don't even know they have it. In addition, the disease has been relatively uncommon up until now, meaning most populations have no immunity against it.
The WHO has also declared that Zika-virus associated microcephaly and Guillain-Barré syndrome are a public health emergency of international concern.
Treatment For Zika
Unfortunately, there is no specific treatment available for Zika, although scientists have identified a gene pathway vital for Zika transmission that may represent a potential pathway for treatment, and three drugs have been identified that may potentially slow the effects of the virus in pregnant women.
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.
Supportive therapy (such as fluids, acetaminophen, rest) may make people more comfortable. Aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs) are not recommended until Dengue Fever has been ruled out to reduce the risk of bleeding.
People with Zika virus infection should be careful to avoid mosquito bites to reduce spreading the disease to others, and no traveler should donate blood within 28 days of traveling to a Zika-infected area.
A number of vaccines are currently being developed against Zika; however, at least one major company has pulled the plug on the development of their vaccine. Given the reduction in the number of cases of Zika in 2017, and a lack of understanding of the epidemiology of the virus, it may be lucky if any vaccines make it to market.
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, experts still consider it 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: Important Questions Answered
- Zika Spreading Rapidly Through Puerto Rico: CDC. Drugs.com News June 17, 2016 https://www.drugs.com/news/zika-spreading-rapidly-through-puerto-rico-cdc-61656.html
- Cumulative Zika Virus Disease Case Counts in the United States, 2015-2017. centers for Disease Control and Prevention. https://www.cdc.gov/zika/reporting/case-counts.html
- Walton AG. (Feb. 6, 2016) Zika Virus Transmittable Through Sex; Unclear Risk From Saliva, Urine. Forbes. http://www.forbes.com/sites/alicegwalton/2016/02/06/zika-virus-transmittable-through-sex-risk-from-saliva-urine-is-unclear/#178f9fcd3cf8
- Report Hints Zika Can Spread Through Oral Sex. Drugs.com News. June 3, 2016. https://www.drugs.com/news/report-hints-zika-can-spread-through-oral-sex-61491.html
- Zika Can Also Strike Eyes of Adults: Report. Drugs.com News. June 22, 2016. https://www.drugs.com/news/zika-can-also-strike-eyes-adults-report-61708.html
- Timing of Zika Infection in Pregnancy May Be Key to Birth Defect Risk. June 25, 2016. https://www.drugs.com/news/timing-zika-infection-pregnancy-may-key-birth-defect-risk-61629.html
- Couples Living in Zika Areas Should Delay Pregnancy, WHO Advises. Drugs.com News. June 10, 2016. https://www.drugs.com/news/couples-living-zika-areas-should-delay-pregnancy-advises-61575.html
- DermnetNZ.org. Zika Virus. Updated Jan 30, 2016. http://www.dermnetnz.org/viral/zika.html
- Faye O, Faye O, Diallo D, et al. Quantitative real-time PCR detection of Zika virus and evaluation with field-caught Mosquitoes. Virol J. 2013; 10: 311. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4016539/
- Boseley S, Watts J. (February 1, 2016) World Health Organization Declares Zikus Virus Public Health Emergency. The Guardian. http://www.theguardian.com/world/2016/feb/01/zika-virus-world-health-organisation-declares-global-health-emergency
- Zika virus. Centers for Disease Control and Prevention. Updated Nov 2017. http://www.cdc.gov/zika/index.html
- Outcomes of Pregnancies with Laboratory Evidence of Possible Zika Virus Infection, 2015-2017. Centers for Disease Control and Prevention. https://www.cdc.gov/zika/reporting/pregnancy-outcomes.html
- Berkley S. Is there a future for a Zika vaccine? Sept 18, 2017. StatNews https://www.statnews.com/2017/09/18/zika-vaccine-future/
- World Map of Areas with Risk of Zika. Centers for Disease Control and Prevention. https://wwwnc.cdc.gov/travel/page/world-map-areas-with-zika