This update provides a general overview of Zika virus, including symptoms of infection, diagnosis, treatment and strategies for prevention. All communities aﬀected by mosquito-borne illnesses such as Zika virus infection can beneﬁt from practicing personal protection against mosquito bites and measures to reduce mosquito populations.
Even a Zika-infected person who does not have symptoms can pass Zika through sex; this includes vaginal, anal and oral sex as well as the sharing of sex toys. People experiencing symptoms of Zika virus infection are encouraged to go to the nearest health facility to be evaluated and treated. However, it is important to note that as many as 80 percent of people infected with Zika virus will not show any symptoms.
Diagnosis and reporting of illness helps local health authorities accurately estimate the scope and impact of an infectious disease outbreak and respond appropriately. This rapidly evolving outbreak has many important implications for reproductive, maternal, newborn and child health services in aﬀected areas.
In recent months, concern has grown rapidly about the potential public health threat from a multicountry outbreak of Zika virus infection. Knowledge about and public health response to this virus, which previously had limited attention, are evolving quickly. Currently, outbreaks are occurring in multiple countries concentrated in Latin America and the Caribbean, but spread of Zika virus will likely continue. Understanding how Zika virus transmission occurs and how it can be prevented are important for combatting this outbreak.
Zika virus is transmitted primarily through the bite of an infected Aedes mosquito, the same mosquito that transmits dengue fever and chikungunya, but diﬀerent from the mosquito that transmits malaria. Mosquitos that become infected when they feed on someone infected with Zika virus can spread it to other people through bites (primarily biting during the daytime hours). Zika virus has been detected in the fetuses of some women; transmission around the time of delivery has also been reported. To date, no reports suggest infants could get Zika virus from breastfeeding, and mothers are encouraged to breastfeed even in areas where Zika virus is found. Transmission of Zika virus through blood transfusion has also occurred.
Transmission of Zika virus through sexual contact has been conﬁrmed, and transmission has occurred in the absence of symptoms (Box 1) of Zika virus infection.
Zika virus infection has been associated with a ﬂu-like illness that can be similar to dengue or chikungunya and usually lasts less than a week. However, as many as 80 percent of people have no symptoms. The time between exposure to Zika virus and symptoms is not clear, but is probably a few days to a week.
Box 1. Symptoms of Zika Virus Infection
Note: As many as 80 percent of people infected will show no symptoms.
Currently, diagnostic testing for Zika virus is very limited. In some settings, diagnosis may be based on symptoms and recent history (such as mosquito bites or travel to an area with Zika virus transmission). Outside of countries reporting active transmission, travelers to and from Zika virus–aﬀected areas appear to be the group most at risk of acquiring Zika virus.
No speciﬁc antiviral treatment exists for Zika virus infection. Supportive care may include increased rest, ﬂuids, and pain-relieving and fever-reducing medications. To reduce risk of excessive bleeding, people with suspected cases of Zika should avoid aspirin and other nonsteroidal anti-inﬂammatory drugs unless dengue can be ruled out. People infected with Zika virus should also protect themselves from further mosquito exposure during the ﬁrst few days of illness to reduce the risk of local transmission to others. Once a person has been infected with Zika virus, it is believed that he or she is probably protected from future infection with Zika.
No vaccine is yet available for prevention of Zika virus infection. Personal preventive measures for Zika virus are similar to those for other mosquito-borne illnesses (Box 2). Note that Aedes are primarily daytime biters and are most active about 2 hours after sunrise and before sunset, but will bite at night as well, preferring to live near people and bite indoors.
Box 2. Protect against Mosquito-Borne Illness
Consistent and correct use of condoms may prevent sexual transmission of Zika virus to an uninfected partner. The CDC recommends that men who have lived in or traveled to an area with active Zika virus transmission should abstain from sex or use condoms correctly every time for vaginal, anal and mouth-to-penis sex with pregnant sexual partners for the duration of the pregnancy.
Controlling mosquitos requires removing, destroying and managing the habitats where they reproduce. Controlling mosquito breeding sites (Box 3) can also help to reduce exposure to bites. All households and businesses can take action to contribute to mosquito control. During a Zika virus outbreak, health authorities may advise spraying of insecticides.
Zika virus has been confirmed as cause of the following health problems:
Understanding whether these problems are due to Zika virus infection will require further studies.
Box 3. Measures to Reduce Mosquitos
Particularly in settings with active Zika virus transmission, members of the public and health care providers may be anxious about Zika virus infection and its possible consequences. Pregnant women are susceptible to infectious diseases like Zika virus, as well as malaria and HIV; antenatal care is a key opportunity for providers to reinforce to all pregnant women the need for comprehensive care, including prevention and treatment. Health care providers should counsel their antenatal care clients on the following important actions:
Providers should stay up to date with evidence-based recommendations for the care of pregnant women (such as those provided by the CDC), as guidance documents have important details about appropriate types of laboratory testing and other aspects of clinical care. Pregnant women with symptoms of Zika virus infection should be tested by rRT-PCR (real-time reverse transcription polymerase chain reaction) within 14 days of the start of symptoms.
Pregnant women with exposure to Zika but without symptoms may be screened with serologic testing 2–12 weeks after the last possible exposure. Asymptomatic women who reside in areas with active Zika transmission should have Zika virus–specific immunoglobulin M testing during routine antenatal care in the first and second trimesters. Those who test positive should immediately receive further testing by rRT-PCR (a positive rRT-PCR test provides definitive diagnosis of Zika virus infection). Local health officials can decide when to test asymptomatic pregnant women, based on information about the extent of Zika virus transmission and laboratory capacity.
Pregnant women with conﬁrmed Zika virus infection should be counseled on all available options for management of the pregnancy and be referred to specialist care, if available. Where capacity exists, fetuses and infants of women infected with Zika virus during pregnancy should be evaluated for possible congenital infection and neurologic abnormalities. Health facilities in regions with Zika virus transmission should be aware of potential increases in neurologic syndromes and congenital malformations.
While ultrasound can detect some cases of microcephaly during pregnancy, some abnormal findings associated with congenital Zika syndrome might not be readily seen on ultrasound. A range of evaluations and growth monitoring strategies are recommended for babies who may have been affected by maternal Zika virus. While no speciﬁc treatment exists for microcephaly, early intervention may help babies improve their development.
In some countries currently aﬀected by Zika virus transmission, the national government has called for women to avoid or postpone pregnancy, due to the possible association between Zika virus infection in pregnancy and microcephaly and other poor health outcomes in infants. Current global recommendations do not include this precaution. However, all women of reproductive age and their partners should have access to information about healthy child spacing and contraceptive options, with the option to adopt the family planning choices that are right for them, regardless of the local status of Zika virus transmission. Health care providers must, as always, maintain attention to the core principle of voluntarism in family planning. Decisions on whether to use family planning are often not in the hands of women alone, and men should be included in family planning counseling and messaging strategies, as appropriate. Demand for family planning services—including interest in long-acting reversible contraception and strain on the availability of contraceptive supplies—may increase, without a concomitant dedication of additional resources for family planning.
Health care providers in areas aﬀected by active Zika virus transmission could see an increased demand for pregnancy termination, regardless of local restrictions on abortion services, highlighting the continued importance of preventing unsafe abortion. Providers supporting postabortion care services should also be aware of the potential impact on demand for services and the need to support the quality of postabortion care in Zika- aﬀected areas.
Information about the Zika virus is changing rapidly. You can stay abreast of this developing public health issue and recommended public health response using the following links, which include sources for this brief and several sites that provide regular Zika virus updates.