Zika virus disease

Zika is an infection caused by the Zika virus. It spreads mainly through the bite of an infected Aedes mosquito. These mosquitoes are found in many tropical and subtropical areas and usually bite during the day, although they can also bite at night.

Most people with Zika have no symptoms. When symptoms occur, they are usually mild and last several days to about a week. Hospital treatment is uncommon, and death from Zika itself is rare.

Zika matters mainly because the virus can pass from a pregnant person to the developing baby. Infection during pregnancy can cause serious problems with brain, eye, and nervous system development. Zika can also occasionally trigger Guillain-Barré syndrome, a condition that causes muscle weakness because the immune system attacks nerves.

Areas with current or past Zika transmission can change. Public health travel information is therefore more useful than older outbreak maps.

Only a minority of infected people develop noticeable symptoms. Symptoms usually begin 3 to 14 days after infection.

Common symptoms include:

• A flat or slightly raised rash, often spreading across the body
• A mild fever
• Pain or swelling in the joints, especially the hands and feet
• Red or irritated eyes without thick discharge

Some people also have headache, muscle pain, tiredness, or pain behind the eyes. Symptoms can resemble dengue, chikungunya, and other infections spread by mosquitoes.

Most symptoms settle within several days to a week. Tiredness or joint discomfort may take longer to disappear in some people.

Seek medical assessment if symptoms develop after travel to, or residence in, an area with Zika transmission. This is especially important during pregnancy or when a sexual partner has had a possible exposure.

Zika is caused by the Zika virus, which belongs to the same virus family as dengue and yellow fever.

The main route of infection is a bite from an infected Aedes mosquito. A mosquito becomes infected after biting someone who has the virus in their blood. It can then spread the virus through later bites.

Zika can also spread:

• Through vaginal, anal, or oral sex
• From a pregnant person to the developing baby
• Through infected blood products, although screening reduces this risk in many places
• Through accidental laboratory exposure

Zika does not usually spread through everyday contact such as touching, sharing food, coughing, or sneezing.

Your chance of exposure is higher if you live in or travel to an area where Zika is being transmitted and are bitten by mosquitoes. Sexual contact with someone recently exposed to Zika can also carry a risk, even if that person never developed symptoms.

Pregnancy does not appear to make Zika symptoms more severe, but infection can affect the pregnancy and developing baby.

Symptoms alone cannot confirm Zika because several other infections can look similar. A healthcare professional will consider your symptoms, pregnancy status, recent travel, place of residence, mosquito exposure, and sexual exposure.

A nucleic acid amplification test, or NAAT, looks for the virus's genetic material in blood or urine. A positive NAAT confirms a current or recent infection. However, the virus remains in these fluids for a limited time, so a negative result does not always exclude infection.

Antibody blood tests look for the immune system's response to Zika. These tests can sometimes help when viral RNA is no longer detectable. Results may be difficult to interpret because Zika antibodies can react with related viruses, especially dengue. Previous infection or vaccination against a related virus can also affect the result.

Testing recommendations differ according to symptoms, exposure, pregnancy, and local patterns of Zika and dengue. Routine testing is not generally used for every person without symptoms. Public health laboratories may be involved because Zika testing is specialised.

During pregnancy, ultrasound scans may be offered to monitor fetal growth and development when there has been confirmed or possible exposure. An ultrasound cannot by itself prove whether Zika infection occurred.

There is no specific antiviral medicine that removes Zika virus. Most people recover at home with supportive care while their immune system clears the infection.

Management usually includes rest, enough fluids to prevent dehydration, and medicine such as acetaminophen, also called paracetamol, for fever or pain when it is safe for you.

Avoid aspirin and nonsteroidal anti-inflammatory drugs, such as ibuprofen or naproxen, until dengue has been ruled out. Dengue can increase the risk of bleeding, and these medicines could make that risk worse. If you take aspirin or another medicine for an existing condition, get medical advice before changing it.

If you are pregnant, discuss any medicine with your maternity care team or pharmacist. Follow-up may include additional ultrasound scans and planning for assessment of the baby after birth.

People with symptoms should take steps to prevent mosquito bites. This helps stop mosquitoes from picking up the virus and passing it to someone else.

Most people do not develop complications.

The main concern is infection during pregnancy. Zika can pass through the placenta and affect the developing baby. Possible outcomes include pregnancy loss, stillbirth, premature birth, and congenital Zika syndrome.

Congenital Zika syndrome describes a pattern of conditions present from birth. It can include:

• A smaller-than-expected head and abnormal brain development
• Eye damage and problems with vision
• Hearing loss
• Stiff joints or limited movement
• Feeding, movement, learning, or developmental difficulties

Not every Zika infection during pregnancy harms the baby. It is usually not possible to predict the outcome from symptoms alone, and people without symptoms can still pass the virus to a developing baby.

A rare complication in adults is Guillain-Barré syndrome. It occurs when the immune system mistakenly attacks the nerves. Tingling or weakness may begin in the legs and move upward. Severe cases can affect swallowing or breathing and need hospital care.

Other nervous system complications, including inflammation of the brain or spinal cord, are uncommon.

There is no approved vaccine that routinely prevents Zika. Prevention focuses on avoiding mosquito bites and sexual transmission.

In places where Zika may occur, use insect repellent registered with the relevant national authority and follow the label. Approved repellents can generally be used during pregnancy when used as directed. Wear clothing that covers the arms and legs, use window screens or air conditioning, and sleep under a mosquito net when rooms are not well screened.

Empty or cover containers that collect water, such as buckets, plant saucers, and open water tanks. Aedes mosquitoes can breed in small amounts of standing water close to homes.

Zika can remain in semen longer than it remains in blood. Current US guidance advises using condoms correctly every time or avoiding sex for:

• At least three months after possible exposure for a partner who produces semen
• At least two months after possible exposure for a partner who does not produce semen
• The entire pregnancy when either partner has possible exposure and the other is pregnant

The timing starts from symptom onset, diagnosis, or departure from an area with Zika risk if there were no symptoms. Local guidance may differ, so check current public health advice when planning pregnancy or travel.

For most people, Zika is a short-term infection. Fever, rash, red eyes, and joint pain usually improve within a week. The virus does not normally cause an ongoing infection, although viral material can remain in some body fluids after symptoms have ended.

You may need to rest and reduce activity for several days. Return to usual activities as your energy and symptoms allow. Continue mosquito and sexual precautions for the recommended period even after you feel well.

Long-term follow-up is not usually needed after an uncomplicated infection in someone who is not pregnant. Arrange routine follow-up if symptoms are not improving, joint pain continues, or you remain concerned about an exposure.

Pregnancy needs a different follow-up plan. Your maternity team may discuss testing, ultrasound monitoring, and assessment of the baby after birth. Some effects of congenital infection, including vision, hearing, movement, or developmental differences, may become clearer over months or years. Early childhood services can provide support if difficulties appear.

Contact a healthcare professional promptly if you develop possible Zika symptoms after relevant travel, mosquito exposure, or sex with someone who may have been exposed.

Prompt, non-emergency advice is particularly important if:

• You are pregnant or could be pregnant
• You are planning a pregnancy after possible exposure
• A newborn may have been exposed during pregnancy
• Symptoms are worsening or not improving after about a week

Seek urgent medical care for new tingling, increasing muscle weakness, difficulty walking, facial weakness, or trouble swallowing. These can be signs of Guillain-Barré syndrome.

Call emergency services for difficulty breathing, rapidly worsening weakness, fainting, confusion, or inability to stay awake.

Severe abdominal pain, repeated vomiting, unusual bleeding, or marked drowsiness also need urgent assessment. These symptoms are not typical of uncomplicated Zika and may suggest dengue or another illness requiring prompt care.

Can I have Zika without knowing it?

Yes. Most infected people do not develop symptoms. A lack of fever or rash does not completely rule out infection, which is why exposure history matters during pregnancy.

How long does Zika last?

Symptoms usually last several days to about a week. The virus may remain in semen and some other body fluids after symptoms have resolved, so prevention measures need to continue for longer.

Can I catch Zika from another person?

Zika is not spread by ordinary social contact. It can spread through sex, from a pregnant person to a developing baby, and rarely through infected blood or laboratory exposure.

Does Zika during pregnancy always harm the baby?

No. Many pregnancies do not have an affected outcome, but infection can cause serious fetal complications. Symptoms and routine scans cannot always predict whether a baby has been affected, so specialist follow-up may be offered.

Can I get Zika more than once?

A previous infection is thought to produce immunity, but the strength and duration of that protection are not fully understood. Continue recommended mosquito precautions even if you have had Zika before.

Can I breastfeed if I have Zika?

Zika virus genetic material has been found in breast milk, but transmission through breastfeeding has not been confirmed. The World Health Organization and US Centers for Disease Control and Prevention advise that the benefits of breastfeeding outweigh the possible risk.