Zika Virus Infection
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Zika virus infection is a mosquito-borne viral infection
that typically causes no symptoms but can cause fever, rash, joint pain, or
infection of the membrane that covers the white of the eye (conjunctivitis, or
pinkeye). Zika virus infection in a pregnant woman can cause microcephaly (a serious
birth defect) and eye abnormalities in the baby.
The Zika virus is spread by mosquitoes, but it can also be
spread through sexual intercourse, through blood transfusions, and from a
pregnant woman to her baby before or during birth.
Symptoms of Zika
virus infection, if they occur, are usually mild.
Doctors suspect Zika based on a person’s symptoms and recent
travel history and confirm the diagnosis based on results of blood or urine
tests.
The best ways to prevent Zika virus infection are to avoid
being bitten by mosquitoes and to avoid unprotected sex with a partner who has
or may have the infection.
There is no specific treatment for Zika virus infection, but
rest, plenty of fluids, and acetaminophen to relieve fever and pain can help.
The Zika virus, like the viruses that cause dengue, yellow
fever, and chikungunya disease, is an arbovirus, spread by a certain species of
mosquito, the Aedes mosquito, which breeds in areas of stagnant water. These
mosquitoes prefer to bite people and live near people, indoors and outdoors.
They bite aggressively during the day indoors and in shady areas outdoors. They
are most active during the several hours after sunrise and before sunset. They
also bite at night.
Overview of Zika Virus Infection
Overview of Zika Virus Infection
In 1947, the Zika virus was first identified in monkeys in
the Zika Forest of Uganda. It was relatively unknown until 2007, when the first
large-scale outbreaks occurred in the South Pacific islands. In May 2015, local
transmission was reported in South America, then in Central America and in the
Caribbean, reaching Mexico by late November 2015. Local transmission means that
people are bitten by an infected mosquito where they live or work, as opposed
to becoming infected while they were traveling.
As of May 2017, cases of locally transmitted Zika virus
infection were reported in Miami-Dade County in southeastern Florida and
Brownsville, Texas. As of December 2019, no new cases of locally transmitted
Zika virus have been reported in the continental United States. Zika virus
infection has been reported in travelers returning to the United States after
travel to countries where the virus is transmitted locally.
The Centers for Disease Control and Prevention (CDC) issues
travel alerts when outbreaks occur. As of December 2019, there are no areas
with Zika outbreaks.
Transmission of Zika Virus
During the first week of infection, Zika virus is present in
blood. When mosquitoes bite an infected person, they ingest blood containing
the virus. The virus replicates in the mosquitoes and, after a few days, when
the mosquitoes bite another person, they can transmit the virus to that person.
People who have traveled to areas where Zika virus infection
is common may have Zika virus in their blood when they return home. If they
live in an area with Aedes mosquitoes, the mosquitoes may bite them, then
spread the virus to other people living in the area, resulting in local
transmission of the Zika virus.
Although the Zika virus is usually spread by mosquitoes, it
may be spread in other ways:
Through sexual intercourse (vaginal, anal, or oral sex) and
the sharing of sexual devices
From an infected pregnant woman to her baby before or during
birth
Through blood transfusion or organ transplantation
Through accidental exposure in a laboratory
People with Zika virus infection can transmit the virus
through sexual intercourse in many circumstances:
If the infection never causes any symptoms
Before their symptoms start
While they have symptoms
After their symptoms end
Zika virus remains in semen much longer than it remains in
blood and other body fluids. It can be spread by infected men to their sex
partners (male or female) through unprotected (no condom) sexual intercourse,
including vaginal, anal, and oral sex (see also Zika: Sexual Transmission and
Prevention).
The Zika virus also remains in vaginal fluids after it
disappears from blood and urine. Infected women can spread the virus to their
male partner during sexual intercourse.
Transmission by blood transfusion has been reported in
Brazil. However, at present, no cases of transmission by blood transfusion have
been confirmed in the United States.
The Zika virus can be spread from mother to child during
pregnancy or around the time of birth.
At present, there have been no reports of infants becoming
infected with Zika virus through breastfeeding. Even though the genetic
material of Zika virus has been found in breast milk, risk of transmission from
breast milk is outweighed by the nutritional benefits of breast milk for the
infant.
Symptoms of Zika
Virus Infection
Most people who become infected with the Zika virus have no
symptoms, and many do not know they are infected. If symptoms occur, they are
usually mild. Infections severe enough to require hospitalization are uncommon.
Death due to Zika virus infection is rare.
Did You Know...
Most people with Zika virus infection do not have symptoms,
and many do not know they are infected.
Symptoms of Zika virus infection include fever, conjunctivitis
(pinkeye), joint and muscle aches, pain behind the eyes, headache, and a red,
bumpy rash. Symptoms last 4 to 7 days.
Rarely, Guillain-Barré syndrome develops after a Zika virus
infection. Guillain-Barré syndrome is a nerve disorder that causes muscle
weakness and a pins-and-needles sensation or loss of sensation that usually
lasts for a limited time.
Microcephaly and other abnormalities in babies
Zika virus infection during pregnancy can cause microcephaly
or other problems in the baby. Microcephaly refers to an abnormally small head.
The head is small because the brain does not develop normally and is small.
Babies infected before birth can have many problems besides
microcephaly, sometimes including:
Seizures
Delays in development (for example, children may have
problems with speech and may sit, stand, and walk later than expected)
Intellectual disability
Problems with movement and balance
Feeding problems, such as difficulty swallowing
Hearing loss
Vision problem
In the United States, several cases of microcephaly have
been linked to the Zika virus. The mothers of these babies were probably
infected when they traveled to a country where Zika virus infection is common.
Zika virus infection can cause other abnormalities in the
brain and in the eyes (including cataracts). Infected babies may have excess
skin on the scalp and, rarely, joints with a limited range of motion (such as
clubfoot).
Diagnosis of Zika Virus Infection
Blood and urine tests
Doctors suspect Zika virus infection based on symptoms and
on the places and dates of travel. However, symptoms of Zika virus infection
resemble those of many tropical diseases (such as malaria, dengue, and other
mosquito-borne viral infections), and it occurs in the same areas as these
infections. Thus, tests are needed to confirm Zika virus infection.
Blood or urine tests can detect the virus if tests are done
within a week or two after symptoms begin. These tests may use the polymerase
chain reaction (PCR) technique, which increases the amount of the virus’s
genetic material and thus makes the virus easier to detect. Tests are also done
to check for Zika virus antibody in the blood.
Currently, men who may have been exposed to the Zika virus
are not tested to determine whether they are infected and thus at risk of
transmitting the virus through sexual intercourse. Instead measures to prevent
transmission (such as condoms) are recommended whenever people who may have
been exposed to the Zika virus have sexual intercourse (including vaginal,
anal, and oral sex).
Testing pregnant women
If pregnant women have traveled to areas where Zika virus
infection is common, blood tests for Zika virus are usually done—whether women
have symptoms of Zika virus infection or not. Also, if pregnant women may have
been exposed to Zika virus, ultrasonography is done to determine whether the
fetus is developing normally.
If pregnant women live in areas where Zika virus infection
is common, Zika virus infection is a risk throughout pregnancy. If they develop
symptoms suggesting Zika virus infection, tests are done during the first week
of illness. If they do not have symptoms, doctors usually do tests for Zika
virus at the first prenatal visit. If the results are negative, another test is
done during the middle of the 2nd trimester to check again for infection.
Ultrasonography to check on the fetus’s development is done at 18 to 20 weeks
of pregnancy.
Testing babies
If a pregnant woman traveled to or lives in an area where
Zika virus infection is common, whether the baby should be tested for Zika
virus depends on the following:
What the mother's Zika virus test results are
Whether the baby has microcephaly, other brain
abnormalities, and/or eye abnormalities
If mothers have positive Zika virus test results, the baby
is tested for Zika virus.
If mothers have negative Zika virus test results or were not
tested for Zika virus and their baby does not have microcephaly or another
abnormality, no testing is needed.
If the baby has microcephaly or another brain abnormality
that can be caused by Zika virus infection, the baby is tested for Zika virus,
regardless of the mother's test results.
Prevention of Zika Virus Infection
The Centers for Disease Control and Prevention (CDC) has
recommended that pregnant women not travel to areas with ongoing Zika virus
outbreaks (see also Zika: Pregnant Women). Before travel to areas with risk of
Zika virus infection, the CDC recommends pregnant women talk with their doctor
about the risks of infection by that virus and about the precautions to be
taken to avoid mosquito bites during the trip.
Currently, there is no vaccine to prevent Zika virus
infection, although research to develop a vaccine is progressing.
Prevention of transmission of Zika virus by mosquitoes
Prevention of Zika virus infection depends on control of
mosquitoes in areas where Zika virus infection is common and on prevention of
mosquito bites when traveling to such areas.
To prevent mosquito bites, people should take the following
precautions:
Wear long-sleeved shirts and long pants.
Stay in places that have air conditioning or that use window
and door screens to keep mosquitoes out.
Sleep under a mosquito bed net in places that are not
adequately screened or air-conditioned.
Use Environmental Protection Agency–registered insect
repellents—with ingredients such as DEET (diethyltoluamide) or other approved
active ingredients—on exposed skin surfaces.
Treat clothing and gear with permethrin insecticide (do not
apply it directly to the skin).
For children, the following precautions are recommended:
Do not use insect repellent on infants under 2 months old.
Do not use products containing oil of lemon eucalyptus
(para-menthane-diol) on children under 3 years old.
For older children, adults should spray repellent on their
own hands and then apply it to the children's skin.
Dress children in clothing that covers their arms and legs,
or cover the crib, stroller, or baby carrier with mosquito netting.
Do not apply insect repellent to the hands, eyes, mouth, or
cut or irritated skin of children.
Prevention of sexual transmission of Zika virus
The Zika virus can be sexually transmitted from men to their
sex partner (male or female) and from women to men. The CDC has made
recommendations about preventing Zika virus from being transmitted during
sexual intercourse (CDC: Zika: Sexual Transmission and Prevention).
For pregnant women, precautions to prevent sexual
transmission of the Zika virus are particularly important. If their partner
(male or female) lives in or has traveled to an area where Zika virus infection
is common, the couple should use a preventive measure for the entire duration
of the pregnancy. The couple should do one of the following:
Abstain from sex (vaginal, anal, or oral)
Consistently and correctly use a barrier birth control
method during sex (vaginal, anal, or oral)
This recommendation applies whether the partner has symptoms
or not because most Zika virus infections do not cause symptoms, and when
symptoms do develop, they are usually mild.
The CDC also provides recommendations when there is no
existing pregnancy. The time periods for men and women differ because the Zika
virus remains in semen longer than in other body fluids.
Men who have traveled to an area with current or past Zika
virus transmission should
Use condoms or abstain from sex for at least 3 months after
he returns, or from the start of symptoms or the date he was diagnosed with
Zika.
Women who have traveled to an area with current or past Zika
virus transmission should
Use condoms or abstain from sex for at least 2 months after
she returns, or from the start of symptoms or the date she was diagnosed with
Zika.
Partners who have both traveled to an area with current or
past Zika virus transmission should
Not sharing sex devices can also reduce the risk of sexual
transmission.
Prevention of transmission of Zika virus through blood
transfusion
The risk of Zika virus transmission through blood
transfusions is considered extremely low. Nonetheless, the US Food and Drug
Administration (FDA) recommends that blood centers in the United States screen
donated whole blood and blood components for Zika with a blood screening
nucleic acid test (see CDC: Zika and Blood Transfusion).
Treatment of Zika Virus Infection
Supportive care
There is no specific antiviral drug for Zika virus infection.
Treatment of Zika virus infection is supportive. It includes
the following:
Rest
Fluids to prevent dehydration
Acetaminophen to relieve fever and pain
People who may have Zika virus infection should not take
aspirin and or other nonsteroidal anti-inflammatory drugs (NSAIDs) until dengue
has been ruled out. If people have dengue and take aspirin or another NSAID,
the risk of excessive bleeding (hemorrhage) is increased. Dengue weakens blood
vessels, making them more likely to break or leak, and NSAIDs make blood less
likely to clot. Also, because of the risk of Reye syndrome, children (aged 18
years and under) should not be given aspirin.
If the Zika virus is detected in pregnant women, doctors may
recommend that ultrasonography be done every 3 to 4 weeks to monitor how the
fetus is developing. Doctors may refer women to a maternal-fetal medicine or
infectious disease specialist with expertise in pregnancy management.