Zika Virus Infection

There are four primary vectors by which Zika can spread:

1. Through Aedes mosquitoes. These make up one of the three most common mosquito genera worldwide, including in the United States. When one of these mosquitoes bites someone infected with Zika, it can then bite someone else and transmit the virus.
2. Through bodily fluids during sexual contact.
3. Through a blood transfusion. Though reported cases have been extremely rare, it is technically possible for Zika to be transmitted this way.
4. From a pregnant woman to her developing fetus. This is where Zika presents the greatest danger, because in a minority of cases it can cause serious developmental problems and congenital birth defects, including microcephaly (smaller than expected head size).

If you are pregnant or plan on becoming pregnant, it is a good idea to speak with your healthcare provider about precautions to avoid Zika, especially if you live in or will be traveling to geographic regions at a high risk for the disease. While there was a serious outbreak of the virus in 2015 and 2016—primarily in Brazil and then extending throughout Latin America and into the United States—the virus has been largely under control since then. It is always possible that another outbreak could flare up in the future, and the CDC has a website to monitor for Zika travel health advisories around the world.

Only about 1 in 5 people with Zika have symptoms. These include the following:

• Fever
• Headache
• Joint pain (arthralgia)
• Muscle aches (myalgia)
• Redness in the eyes (conjunctivitis)
• An itchy skin rash with raised and flat red areas (maculopapular rash)

The incubation period for Zika lasts between 3 and 14 days, and symptoms usually last for several days up to a week. Zika can be transmitted to others whether symptoms are present or not.

In rare cases, patients who have contracted Zika have developed brain diseases, including Guillain-Barré syndrome (GBS), encephalopathy (a broad term for damage or functional changes to the brain), and simultaneous inflammation of the brain and its surrounding membrane (meningoencephalitis). However, it bears repeating that these instances have been extremely uncommon. Zika has also occasionally also led to inflammation in the eyes or spinal cord (uveitis and myelitis, respectively) and low blood platelet count (thrombocytopenia).

Zika virus can be detected through laboratory analysis of patients’ blood, or in some cases, urine. Typically, healthcare providers will only test for Zika if patients have traveled to a location with a high risk for Zika or if they have symptoms. A lab test is necessary because the symptoms of Zika have similarities to those of many other infections, including dengue, malaria, leptospirosis, rubella, measles, group A streptococcal, and so on. 

The virus can be transmitted during pregnancy whether the mother has symptoms or not. Infants may appear asymptomatic at birth but may have neuroimaging results or vision loss that are only detected after birth. If a birthing mother has been exposed to Zika virus within two months of delivery, infants who show signs of fever, rash, conjunctivitis, and joint pain during the first two weeks of life should be tested for infection. 

So far, there are no vaccines or medications available to prevent or treat Zika infections. Acetaminophen (Tylenol, etc.) can provide some symptomatic relief for headaches and joint/muscle pain, but if the infection has not been confirmed as Zika through laboratory analysis, it is best to avoid aspirin, ibuprofen, and naproxen. That is because these and other NSAIDs can cause complications in dengue infections, which have very similar symptoms.

The best course of action is to try to avoid and prevent Zika infection. Especially if you are traveling to a region at high risk for Zika, take measures to protect yourself from mosquito bites by using insect repellent, wearing long-sleeved shirts and pants, and sleeping in areas enclosed by window screens or netting. These approaches are not guaranteed to prevent insect bites, of course, but they will help reduce the risk considerably. If you travel to an area of high risk for Zika, continue practicing mosquito-bite protection for at least three weeks after returning home, even if you do not have symptoms.

If you or your sexual partner has been diagnosed with a Zika infection, with or without symptoms, or if you are traveling to a region at higher risk for Zika, experts recommend using barrier protection (such as condoms) or abstaining from sex for at least two months for females and three months for males. The reason for the difference in these timeframes is because Zika virus can stay active in semen longer than other bodily fluids. 

The World Health Organization states that “research is ongoing to investigate the risk and effects of Zika virus infection on pregnancy outcomes, strategies for prevention and control, and effects of infection on other neurological disorders in children and adults.” Some examples of Zika research include those ongoing at Baylor College of Medicine in Texas, which include efforts to better understand the transmission pathways of the virus, its methods of causing disease and birth defects, and its possible effects on the human immune system. Researchers are also hopeful that their studies can lead to the development of a safe and effective vaccine against the virus. 

Reading scientific studies

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