Zika virus is a mosquito-borne flavivirus primarily transmitted by the bite of an infected mosquito. While its impact on fetal development has received significant attention, the virus also affects adults, causing a range of symptoms and potential health issues.
How Zika Spreads to Adults
The primary way adults contract Zika is through the bite of an infected mosquito from the Aedes genus, mainly Aedes aegypti and Aedes albopictus. These mosquitoes are aggressive daytime biters that thrive near human dwellings. When a mosquito bites a person with an active Zika infection, it can ingest the virus and then transmit it to others.
Beyond mosquito bites, Zika can be transmitted between adults through sexual contact, even if the infected individual is not showing any symptoms. The virus can persist in semen much longer than in other body fluids like blood or urine, making sexual transmission a notable concern. Less common routes of transmission include blood transfusions and organ transplantation, though these are not the main drivers of outbreaks.
Recognizing Zika Symptoms in Adults
A challenge in identifying Zika is that an estimated 80% of infected adults are asymptomatic. For those who do become ill, the symptoms are mild and often mistaken for other illnesses like dengue or chikungunya. The incubation period is between 3 and 14 days.
The most common signs include a low-grade fever, a maculopapular rash (a flat, red area on the skin with raised bumps), joint pain, and conjunctivitis (red eyes). Other reported symptoms are muscle pain and headaches. These symptoms are self-limiting, lasting for two to seven days and resolving without specific medical treatment.
Potential Health Complications in Adulthood
While most adult Zika infections are mild, a small fraction can lead to serious neurological complications. The most well-documented is Guillain-Barré syndrome (GBS), an autoimmune disorder where the body’s immune system attacks its peripheral nerves. This can cause muscle weakness, numbness, and in severe cases, progressive paralysis that may require hospitalization. The onset of GBS symptoms often occurs during or immediately after the acute Zika infection.
Other, rarer neurological issues have also been linked to Zika in adults. These include meningoencephalitis (inflammation of the brain and its surrounding membranes), myelitis (inflammation of the spinal cord), and encephalopathy.
Diagnosing and Managing Zika in Adults
Diagnosing Zika relies on laboratory testing, as its symptoms overlap with other viral illnesses. The primary method during the early phase of infection is a reverse transcriptase-polymerase chain reaction (RT-PCR) test. This test detects the virus’s genetic material (RNA) in blood or urine and is most effective within the first one to two weeks after symptoms begin. After this period, antibody tests can identify a recent infection.
There is no specific antiviral medication to treat Zika, so management focuses on supportive care to alleviate symptoms. This includes rest, hydration, and over-the-counter pain and fever reducers like acetaminophen. It is advised to avoid aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) until dengue fever can be ruled out, to reduce the risk of bleeding complications.
Protective Measures for Adults Against Zika
Preventing Zika infection involves avoiding mosquito bites and preventing sexual transmission. To protect against mosquitoes, use Environmental Protection Agency (EPA)-registered insect repellents on exposed skin. Wearing long-sleeved shirts and long pants provides a physical barrier, and staying in places with air conditioning or well-screened windows reduces exposure.
To prevent sexual transmission, individuals who have traveled to an area with a risk of Zika should use condoms or abstain from sex for a recommended period after their return. Current guidelines suggest that men should take these precautions for at least three months after travel or the start of symptoms, while women should do so for at least two months. Health authorities provide up-to-date travel advisories for regions where Zika is a known risk.