Tai-Ho Chen, J. Erin Staples, Marc Fischer
INFECTIOUS AGENT
Zika virus is a single-stranded RNA virus of the Flaviviridae family, genus Flavivirus.
TRANSMISSION
Transmission occurs through the bite of an infected Aedes species mosquito. Intrauterine, perinatal, sexual, laboratory, and possible transfusion-associated transmission also have been reported. Although Zika viral particles were found in the breast milk of 1 woman, and virus RNA has been detected in breast milk of 2 additional women, transmission of Zika virus through breastfeeding has not been documented.
EPIDEMIOLOGY
Zika virus was first identified in Uganda in 1947. Before 2007, only sporadic human cases were reported from countries in Africa and Asia. In 2007, the first documented Zika virus disease outbreak was reported in the Federated States of Micronesia. In subsequent years, outbreaks of Zika virus disease were identified in countries in Southeast Asia and the Western Pacific. Zika virus was identified for the first time in the Western hemisphere in 2015, when large outbreaks were reported in Brazil. Since then, the virus spread throughout much of the Americas. (See https://wwwnc.cdc.gov/travel/ for current CDC travel notices for Zika virus.)
CLINICAL PRESENTATION
Most Zika virus infections are asymptomatic. Symptomatic infections are generally mild. Commonly reported signs and symptoms include fever, maculopapular rash, arthralgia, and conjunctivitis. Other symptoms include myalgia and headache. During the outbreak in Brazil in 2015, the Ministry of Health of Brazil reported a marked increase in the number of infants born with microcephaly, although it is not known how many of these cases were associated with Zika virus infection. Zika virus RNA was subsequently identified in tissues from several infants with microcephaly and from fetal losses in women who were infected during pregnancy. (See Box 3-06 for more information about Zika and pregnancy.) Guillain-Barré syndrome also has been reported in some patients after Zika virus infection.
DIAGNOSIS
Zika virus infection should be considered in patients with acute onset of fever, maculopapular rash, arthralgia, or conjunctivitis who live in or have traveled to an area with ongoing transmission in the 2 weeks preceding illness onset. Because dengue and chikungunya virus infections share a similar geographic distribution and symptoms with Zika, patients with suspected Zika virus infection should also be evaluated and managed for possible dengue or chikungunya virus infection. Other considerations in the differential diagnosis include malaria, rubella, measles, parvovirus, adenovirus, enterovirus, leptospirosis, rickettsiosis, and group A streptococcal infections.
For people with suspected Zika virus disease, Zika virus rRT-PCR should be performed on urine specimens collected <14 days after onset of symptoms or serum specimens collected <7 days after onset of symptoms. A positive rRT-PCR result confirms Zika virus infection, and no antibody testing is indicated. Serum IgM antibody testing should be performed if rRT-PCR is negative or for samples collected ≥7 days after illness onset. However, these serologic assays can be positive because of cross-reacting antibodies against related flaviviruses, such as dengue or yellow fever viruses. Virus-specific neutralization testing can be used to discriminate between cross-reacting antibodies in primary flavivirus infections, although neutralizing antibodies might still yield cross-reactive results in people who were previously infected or vaccinated against a related flavivirus (secondary flavivirus infection).
Health care providers are encouraged to report suspected Zika virus disease cases to their state or local health departments to facilitate diagnosis and mitigate the risk of local transmission in areas where Aedes species mosquitoes are active. Zika virus disease is a nationally notifiable condition. State health departments should report laboratory-confirmed cases to CDC according to the Council of States and Territorial Epidemiologists case definitions. Pregnant women with laboratory evidence of Zika virus infection should be reported to the US Zika Pregnancy Registry or the Puerto Rico Zika Active Pregnancy Surveillance System for clinical follow-up.