Clinical manifestations

Presentation and course

	• Symptomatic Zika virus infection manifests in about 20% of infected individuals with a mild febrile exanthematic disease.
	• Zika virus clinical disease has low case-fatality rates and resolves spontaneously in most patients in fewer than 7 days.

Approximately 80% of Zika virus infections are asymptomatic, and misdiagnosis of Zika virus disease is very common because signs and symptoms in previously healthy patients resemble other arbovirus infections, such as Chikungunya and dengue. In cases of Zika virus clinical disease, a low-grade fever appears after an incubation of 2 to 14 days (< 38.5°C). The fever is followed by a pruritic rash (erythematous macules and papules), nonpurulent conjunctivitis, headache, myalgia, and arthralgia--notably in the small joints of the hands and feet, sometimes with periarticular edema. The disease is usually mild. Clinical illness is consistent with Zika virus disease if two or more of these previous symptoms are present. The symptoms typically last less than a week; no mortality has been reported from the initial infection phase. Immunity to reinfection occurs following primary infection. Clinical manifestations in infants and children with postnatal infection are similar to those in adults (02).

Prognosis and complications

Zika virus infection has a good prognosis in the vast majority of cases. However, the main complications are neurologic and can lead to severe sequelae, especially in children infected during intrauterine life. Guillain-Barré syndrome, congenital Zika syndrome, and other less frequent neurologic complications have been described in the literature and will be detailed below.

Congenital Zika syndrome. Congenital Zika syndrome occurs through vertical transmission when pregnant women are infected with the Zika virus, a route also associated with spontaneous abortion (46). Some months after the disease outbreak in Northeastern Brazil, an unusual increase in microcephaly cases gave rise to a possible link of the Zika virus and its pathogenesis (49). Microcephaly, intracranial calcification, ventriculomegaly, and ophthalmological findings leading to a chronic nonprogressive encephalopathy syndrome with global developmental delay and epilepsy account for the complete neurologic picture of congenital Zika syndrome (30; 34).

Animal models have brought some light to the pathogenesis of congenital Zika syndrome. Inoculated nonhuman primate pregnant females may or may not develop symptoms. Nevertheless, damage and virus RNA are observed in their placentas, and fetuses show pathology and viral RNA in their brains. Furthermore, the earlier the timing of the inoculation during pregnancy, the greater the extent of the brain damage and possible ocular involvement. Mice models suggest that placental inflammation might be a contributing factor (53).

New insights into possible ways that Zika virus might induce neurologic injury have appeared in the literature, such as changes in DNA methylation, the opening of the receptor potential vanilloid 1 channel (TRPV1), copper imbalance, and oxidative stress (04; 10; 63; 35).

The microcephaly can be such that cranial facial disproportion is observed with redundant occipital skin scalp folds (49). In their systematic review, Freitas and colleagues found microcephaly as the most frequent clinical manifestation of congenital Zika syndrome (30). They classify the described features in live-born babies as either neurologic, osteoskeletal, ophthalmic, or abnormalities in other systems. Hypertonicity, hyperreflexia, asymmetric tonic neck reflex, clenched fists, abnormal posturing, and altered motor reflexes suggest motor neuron involvement. Seizures, irritability, hypoactivity, altered visual fixation and pursuit, or cortical blindness are all findings suggesting diffuse brain injury. Osteoskeletal abnormalities, including arthrogryposis and other distal limb contractions, are also related to nervous system involvement (80). Neurophysiology studies done in seven babies with arthrogryposis depicted a denervation pattern, and on the spinal MRI, done in four cases, spinal cord thinning and a reduction in the thickness of the ventral roots were found (80).

A 2-year follow-up of a cohort of 28 babies showed them to have a nonprogressive course. Not all mothers had a cutaneous rash during pregnancy; all had their offspring referred for congenital microcephaly and had confirmation of Zika virus infection. One of the babies had a normal head circumference at birth, but deviation from normal occurred in the following 2 months. All had global developmental delay with the combination of axial hypotonia with appendicular hypertonia, muscle weakness, hyperreflexia, and retained primitive reflexes, and those were nonprogressive during follow-up. Most of them developed early-onset seizures with features of resistant epilepsy (34).

Intracranial calcification in infants and children can be found in many genetic disorders and congenital infections (68). Table 1 summarizes the imaging findings in congenital Zika syndrome, listing those found in other common congenital infections. Although various central nervous malformations have been reported in congenital Zika syndrome, the most common combination is ventriculomegaly with atrophy and parenchymal or cerebellar calcification (30). An example of this combination is shown in the clinical vignette. The greater severity of the imaging findings and the predominance of calcification localization in the gray-white matter junction are more evident in congenital Zika syndrome than in other common congenital infections.

Table 1. Imaging Findings in Congenital Zika Syndrome in Comparison With Those in Other Common Congenital Infections

Pathology	Calcification localization	Other findings	Reference
Zika	Subcortical (first), followed by basal ganglia; gray-white matter junction appears more frequently	Ventriculomegaly or hydrocephaly, cerebellar abnormalities, corpus callosum abnormalities, microcephaly, periventricular calcifications	(75; Marques et al 2019; 30)
Toxoplasmosis	Widespread	Hydrocephalus	(25; 68)
VZV	Periventricular and basal ganglia		(25; 68)
Rubella	Periventricular and basal ganglia		(25; 68)
CMV	Periventricular	Migrational abnormalities	(25; 68)
HSV	Scattered		(25; 68)
HIV	Basal ganglia		(25; 68)
VZV: varicella-zoster, CMV: cytomegalovirus, HSV: herpes simplex virus, HIV: human immunodeficiency virus

In congenital Zika syndrome, postmortem pathological findings are widespread in the CNS (46; 20). Neuronal migration disorders accompany microcephaly and ventriculomegaly. Midbrain distortion and cerebellar hypoplasia are other common findings. Some inflammatory features, such as parenchyma microglial nodules, perivascular cuffs, and reactive gliosis, are combined with the main findings of extensive calcification and tissue destruction. Neural and glial cells and areas of microcalcification test positive for the Zika virus (46). Leptomeninges may also show inflammatory abnormalities. Spinal tissue shows a distinctive loss of anterior horn cells (20), confirming the topographic location for the arthrogryposis suspected in neurophysiology and imaging studies (80).

In utero, fetal ultrasound can detect some brain malformations (81). A newborn from an endemic or epidemic area with microcephaly should always be screened for Zika virus, even if a history of maternal rash during gestation is not present. The assessment should include Zika virus rRT-PCR on blood specimens and urine samples collected in the first week of life and laboratory evaluation to rule out other congenital infectious etiologies, including toxoplasmosis, syphilis, cytomegalovirus, dengue, rubella, and HIV (60; 32; 34).

Infants with congenital Zika syndrome might have a normal brain circumference at birth and develop postnatal microcephaly or just developmental delay. Thus, babies with the features of chronic encephalopathy such as spastic cerebral palsy or cognitive arrest from an endemic or epidemic area should also be considered potential Zika virus-associated cases.

With longer follow-up, it is now clear that children with congenital Zika syndrome do have diffuse nervous system damage, showing global developmental delay with motor and cognitive manifestations (83; 34). Therefore, a multidisciplinary team is usually needed for the continuous care of those children. Physiotherapists are needed early on for the motor features as in infants with cerebral palsy. As the child grows, a speech therapist should be added for the language delay in most and for dysphagia in some. Later, occupational therapists and other facilitators may be inserted into the health care group. Family members should be incorporated from the beginning to help ensure the daily interventions are followed (73).

Epilepsy is not only frequent in congenital Zika syndrome but has an early start and a tendency to be refractory. Surveillance with EEG and specific medication should be implemented according to seizure type (34; 57).

Normocephalic newborns whose mothers had been diagnosed with Zika virus infection during pregnancy were checked for developmental status at 24 to 30 months of age and compared to control groups. Their outcomes were comparable for developmental status, but vision impairment can be found in the absence of neurodevelopmental delays. Nevertheless, should secondary microcephaly or blindness occur in a normocephalic newborn exposed in utero to Zika virus, poor neurodevelopment is expected (11).

Babies diagnosed with postnatal Zika virus infection in their first year of life may also show compromised neurologic or sensory outcomes on follow-up (59).

Zika virus-associated Guillain-Barré syndrome (Z-GBS). A transient rise in incidence of Guillain-Barré syndrome can be seen during or after infectious outbreaks. An example is a surge and subsequent decline of Guillain-Barré syndrome following the 2014 to 2016 Zika virus outbreak in French Polynesia, Latin America, and the Caribbean. The syndrome’s incidence increased transiently by 2.6 times the background incidence (16).

The first link between Guillain-Barré syndrome and Zika occurred in 2013 during the French Polynesia outbreak (58). An increased incidence of Guillain-Barré syndrome cases occurred 3 weeks after the Zika outbreak. Forty-two patients were documented then, and 41 had IgM antibodies against the Zika virus. Of these, 100% had neutralizing antibodies versus 54% of the control group. These patients presented with generalized muscle weakness, facial nerve palsy, and albuminocytologic dissociation in the CSF; respiratory failure was found in 29%. The most common subtype of Guillain-Barré syndrome was acute motor axonal neuropathy. These cases had a good overall prognosis. At 3 months after discharge, approximately 57% could walk (15).

Several additional studies have confirmed the causal association between a previous Zika virus infection and Guillain-Barré syndrome (Z-GBS) (03; 06; 19; 42). In most patients, the onset suggests a postinfectious illness rather than a parainfectious disease (79; 41; 42).

According to a meta-analysis with all probable cases of Z-GBS published until 2020, Zika virus infection was confirmed in 21%, was likely in 22%, and was suspected in 57% of cases. PCR for Zika virus was positive in 30% of the urine or blood samples tested. The most common clinical findings were: weakness in the limbs in 97%, decreased or absent reflexes in 96%, sensory symptoms in 82%, and facial paralysis in 51%. The average time between infection and neurologic symptoms was 5 to 12 days. Most of the cases presented the electrophysiological demyelinating subtype, and half were admitted to the intensive care unit (41).

An observational study conducted during Brazil’s 2015 to 2016 Zika virus outbreak established a strong association between Zika virus and Guillain-Barré syndrome (07; 28). The study investigated neurologic disorders possibly associated with Zika virus and other arboviruses, individually and by dual infection. Two hundred and one adults participated (median age: 48), with 106 females. A wide variety of neurologic diseases were possibly caused by Zika virus, including Guillain-Barré syndrome, which also overlapped with other arboviruses like Chikungunya.

The pathogenesis of classical Guillain-Barré syndrome, not associated with previous Zika virus infection, is considered a molecular mimicry between gangliosides and molecules present on the surface of infectious agents (for example, Campylobacter jejuni lipopolysaccharide). Recent studies show that a humoral response to C jejuni is possible in a minority of patients but is unlikely to be a key driver of neurologic disease in Z-GBS. It seems that peripheral nerve reactive autoantibodies are a feature of a subset of patients who developed Guillain-Barré syndrome following Zika virus infection, targeting a broad range of peripheral nerve-related antigens (23).

There is evidence suggesting a role of gangliosides in the development of Guillain-Barré syndrome in the context of Zika virus infection. Studies have found that patients with Z-GBS have higher levels of antiganglioside antibodies than those without Guillain-Barré syndrome. The study found that IgM and IgG anti-self antibodies targeted a broad repertoire of gangliosides in patients with Guillain-Barré syndrome. Because Zika virus infects neurons, which contain membrane gangliosides, the antigen presentation of these infected cells may trigger the observed autoimmune anti-ganglioside antibodies, suggesting direct infection-induced autoantibodies as a cause leading to Guillain-Barré syndrome development. This suggests that anti-ganglioside antibodies might contribute to the pathogenesis of Guillain-Barré syndrome in Zika virus-infected individuals (64). However, the exact mechanism of how Zika virus infection leads to the development of Guillain-Barré syndrome through gangliosides is still unresolved. Further mechanistic studies are needed to test this hypothesis and elucidate the role of anti-ganglioside antibodies in Zika-induced Guillain-Barré syndrome. Other authors hypothesize that Zika virus associated Guillain-Barré syndrome relates to molecular mimicry between the viral envelope (E) protein and neural proteins involved in Guillain-Barré syndrome (40). Further studies are still needed to clarify this hypothesis.

In an observational cohort study of Z-GBS from Brazil, most patients were treated with intravenous immunoglobulin. Twenty percent were admitted to the intensive care unit, and 14% were intubated. The median duration of hospital admission was 19 days, and none of the patients died (42).

When comparing patients with Guillain-Barré syndrome with and without Zika virus who were seen in the same period and in the same region (Puerto Rico), there was no difference in duration of hospitalization, frequency of medical complications, or type of treatment used. However, patients with evidence of prior Zika virus infection were admitted more frequently to the intensive care unit and more commonly required mechanical ventilation. Hospital deaths did not differ between patients with and without evidence of Zika virus (26).

The long-term outcome of Z-GBS is consistent with Guillain-Barré syndrome associated with other etiologies in terms of mortality and ongoing long-term morbidity. Additionally, long-term physical and mental status among persons with Z-GBS after 1 year was similar to persons with Guillain-Barré syndrome without Zika. Disability and depression were more common among patients with Guillain-Barré syndrome after 1 year when compared with a normative sample of neighborhood-selected control subjects with Guillain-Barré syndrome (82).

Other neurologic complications associated with Zika virus. Myelitis, encephalitis, meningoencephalitis, acute disseminated encephalomyelitis, sensory polyneuropathy, autonomic dysfunction, cerebrovascular disease with vasculitis, and cranial neuropathy have been described, concomitantly or shortly after Zika virus infection (18; 21; 31; 48; 47; 50; 67; 74; 14; 22; 39; 54; 55; 62; 71; 01; 17; 65; 66).

The association of Zika virus infection with congenital malformations and Guillain-Barré syndrome has strong evidence of causality. That is not the case for these other neurologic manifestations. Most of the reports are of isolated cases or small series of cases. Regardless, the Zika virus should be included in the differential diagnosis of meningitis, encephalitis, myelitis, and peripheral neuropathies of recent, acute, or subacute onset in patients from countries with circulation of Zika virus.

Clinical vignette

A 2-month-old girl from Brazil was assessed for microcephaly. The mother’s pregnancy was complicated by a rash and fever lasting 3 days during the first trimester. Ultrasound at the beginning of the third trimester showed a tiny baby with a small cephalic pole. There was no family history of microcephaly, and both parents had a normal cranial circumference.

Apart from microcephaly, the baby had normal reactions and development for her age and no other general findings. Antibodies for the common congenital infections were negative, and a cranial CT depicted calcifications and poor gyri formation. r-RT-PCR for Zika virus in the baby’s blood was positive. On follow-up, development was delayed, cranial circumference remained below normal values, and epileptic spasms appeared by the end of the first year of life. Although antiepileptic treatment was started early, the seizures persisted, and despite physiotherapy, the developmental delay also continued.

Biological basis

	• Zika virus is a single-stranded RNA flavivirus related to yellow fever, dengue, West Nile, and Japanese encephalitis viruses.
	• Zika virus is transmitted primarily through the bite of infected Aedes species mosquitoes but can also be transmitted from mother to child or by blood transfusion, contact with body fluids, and sexual contact.
	• In humans, following a mosquito bite, Zika virus infects and replicates in fibroblasts and dendritic cells, spreading through the blood to lymph nodes and other organs.

Etiology and pathogenesis

Zika virus is an arthropod-borne virus (arbovirus) of the genus Flavivirus and the family Flaviviridae. The word arbovirus, a contraction of arthropod-borne virus, is an ecological term defining viruses maintained in nature through biological transmission between a susceptible vertebrate host and a hematophagous arthropod, such as a mosquito. Zika virus is related to yellow fever, dengue, West Nile, and Japanese encephalitis viruses. Flaviviruses are spherical, enveloped, single-stranded, positive-sense RNA viruses that are 50 nm in size. The full-length genome is nearly 10.5 to 11 kbp. The genome produces a polyprotein with more than 3000 amino acids. To be mature, the polyprotein is cleaved into three structural (C, PrM, E) and seven nonstructural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS5) (51). Zika virus is a unique flavivirus because it can persist for months in immune-privileged sites (52). Two main lineages of the Zika virus have been reported: African and Asian (38).

Zika virus is transmitted primarily through the bite of infected Aedes species mosquitoes following a sylvatic transmission cycle. Humans, apes, monkeys, sheep, elephants, and goats can also be incidental hosts in the viral lifecycle (02). Zika virus can be transmitted from mother to child (transplacental infection) (09), by blood transfusion, by exposure to body fluids, by organ transplantation (56), and by sexual contact (44; 51). In 2016, the first male-to-male transmission was registered in Texas, United States (02).

Zika virus replication in the mosquito begins in the epithelial cells of the mosquito midgut and proceeds to the salivary glands. The mosquito can spread the virus after a 10-day incubation period when saliva becomes infected. In humans, following a mosquito bite, Zika virus infects and replicates in fibroblasts and dendritic cells, spreading through the blood to lymph nodes and other organs. The incubation period in humans varies from 2 to 14 days, and symptoms appear after 6 to 11 days. In most cases, the infection is self-limiting. In pregnant women, the virus crosses the placenta, and it can replicate in the fetal brain for months, with increasing effects during the early months of pregnancy. Zika virus is cleared within 24 days in 99% of patients (52).

Animal models helped researchers understand the pathogenesis shortly after Zika virus discovery. Zika virus pathological properties leading to neuronal degeneration, particularly located in the mouse hippocampus, indicated its neurotropism (24). This was followed by descriptions of damage of Zika virus in developing mouse brain on astrocytes and neurons with strong glial activation, again in the hippocampus (08). The potential mechanism of Zika virus upregulation replication in vitro was supported by the finding of intracytoplasmic inclusions in infected neurons (78). These inclusions are thought to be viral replication complexes, which are sites of viral RNA synthesis and assembly of new virus particles. The presence of these inclusions suggests that the virus is actively replicating within the neurons, leading to the production of new virus particles. This is supported by studies that have shown that Zika virus can infect and replicate in human neural stem cells, cortical neural progenitors, radial glial cells, and newly differentiating neural progenitors of developing mice. The virus also infects microglial and astroglial cells. The virus modulates cell machinery at several levels to replicate itself and inhibits toll-like receptors-3 signaling, deregulates microRNA circuitry, and induces a chronic inflammatory response in affected cells. Several significant advances have been made to understand the mechanisms of Zika virus-associated neuropathogenesis, but basic and clinical researchers are still striving to find answers to some open questions in the hope of reducing the burden of consequences arising following Zika virus infections (12).

Epidemiology

	• Zika virus may be transmitted to humans by different mechanisms: bite of an infected mosquito, maternal-fetal, sexual, blood transfusion, organ transplantation, and body fluid exposure, including in the laboratory.
	• Zika virus infection occurs as endemic or as outbreaks in Africa, the Pacific islands, Southeast Asia, the Americas, and the Caribbean.
	• The biggest disease outbreak occurred in the Americas between 2015 and 2016, but the number of cases has been declining steadily since then.

Zika virus outbreaks have been described in Africa, the Pacific islands, Southeast Asia, the Americas, and the Caribbean. Updates on the worldwide distribution of Zika virus can be found at the following websites: Pan American Health Organization, Centers for Disease Control and Prevention, and World Health Organization.

On February 1, 2016, the World Health Organization (WHO) declared the Zika virus outbreak an international public health emergency. However, since then, in most countries, cases of Zika are significantly down from the peak. In fact, in November 2016, WHO declared the end of the emergency. Ultimately, the exact decline is hard to measure because many people with no symptoms were never tested for Zika. Most experts say that the decline in Zika cases is due, at least in part, to herd immunity. This is especially true for individuals living in areas with a high concentration of mosquito-based infections. There is also suspected “cross-protection” because Zika virus shares antibodies with the dengue virus and other flaviviruses, but this has not been proven.

Since the Zika virus outbreaks of 2016, reported Zika cases in the Americas have declined by 30- to 70-fold and are now outnumbered by reported dengue cases by a ratio of approximately 200:1. The last confirmed case of locally-acquired Zika in the continental United States was in September 2017. Similarly, the last confirmed positive case in the United States territories was reported in May 2018 (https://www.cdc.gov/zika/hc-providers/testing-guidance.html).

Zika virus may be transmitted to humans by different mechanisms: bite of an infected mosquito (the most common), maternal-fetal, sexual (vaginal, anal, and oral), blood transfusion, organ transplantation, and exposure to body fluids, including in the laboratory (52).

There is no age or gender preference associated with an increased prevalence of infection (29).

The incidence of Zika-related microcephaly has decreased since the peak of the Zika virus outbreak in 2015 and 2016. However, it is still considered a significant public health concern, especially in areas with ongoing Zika virus transmission. More information can be accessed at the following site:www.who.int.

Prevention

• In the absence of an effective vaccine, Zika virus infection can be prevented mainly through insect repellents and the use of condoms in the case of sex with individuals who have traveled to or are living in endemic areas.

According to the Centers for Disease Control, if someone is traveling to a Zika virus endemic region, some precautions should be taken. EPA-registered insect repellents should be used to prevent mosquito bites. These repellents should have one of the following active ingredients: DEET, picaridin, IR3535, oil of lemon eucalyptus, para-menthane-diol, or 2-undecanone. Also, exposed skin should be covered by the use of long-sleeved shirts and long pants. Staying in places with air conditioning or with window and door screens or sleeping under a mosquito bed net are additional measures to prevent mosquito bites. Condoms should be used to avoid sexual transmission. This is especially important if the person or partner is pregnant or planning to become pregnant. After travel, the person should continue using mosquito repellent for 3 weeks after return, even if asymptomatic. That will help prevent spreading Zika to uninfected mosquitoes that can spread the virus to other people. After travel, people should use condoms—or do not have sex—for at least 3 months (men) or 2 months (women) to protect partners. If the partner is pregnant, condoms should be used for the remainder of pregnancy (https://wwwnc.cdc.gov/travel/diseases/zika).

Adenovirus-vectored Zika virus vaccine has been tested in healthy volunteers in different dosing regimens (69). This resulted in antibody response for up to 1 year with no safety concerns. As a phase 1 trial, this must be followed by efficacy studies and mainly in endemic areas.

Differential diagnosis

Confusing conditions

Infection by Zika virus can manifest in a clinically similar way to other arboviral illnesses, such as Dengue, Chikungunya, and West Nile fever. These diseases are sometimes endemic in the same regions as Zika virus and can also lead to neurologic complications, which can be a diagnostic challenge to the clinician. Table 2 summarizes the main clinical and neurologic findings of infection with Zika, Chikungunya, and West Nile viruses.

Table 2. Clinical and Neurologic Findings of the Most Common Arboviruses

Virus or Symptoms	Zika virus	Dengue virus	Chikungunya virus	West Nile virus
Fever	+	++++	++++	++
Rash	++++	++	++	++
Myalgia	++	+++	++	++
Arthralgia	++	+	++++	+
Periarticular edema	++	+	+++	-
Conjunctival hyperemia	+++	+	+	++
Headache	++	+++	++
Neurologic syndromes	Microcephaly, Guillain-Barré syndrome, encephalomyelitis, myelitis, meningoencephalitis, peripheral neuropathy	Encephalopathy, seizures, Guillain-Barré syndrome, mononeuropathy, myelitis	Meningoencephalitis, acute flaccid paralysis, Guillain-Barré syndrome, sensorineural hearing loss	Meningitis, encephalitis, acute flaccid paralysis, brachial plexopathy, demyelinating neuropathy, motor axonopathy, axonal polyneuropathy, motor radiculopathy, myasthenia gravis, cranial nerve palsies
+: frequency of symptom. Adapted from (05).

Other differential diagnoses of acute Zika virus infection are parvovirus B19 infection, rubella, measles, leptospirosis, malaria, and Rickettsial infection.

The neurologic complications of Zika virus, such as Guillain-Barré syndrome, microcephaly, encephalomyelitis, and meningitis or meningoencephalitis, are multicausal and may have infectious or autoimmune causes or may be idiopathic. For a more detailed description of each of these differential diagnoses, the reader is referred to the following articles:

• Microcephaly • Acute inflammatory demyelinating polyradiculoneuropathy • Transverse myelitis • Acute disseminated encephalomyelitis • Viral meningitis

Associated or underlying disorders

Prior dengue infection may be protective against symptomatic Zika virus infection, but further study is needed (33).

Diagnostic workup

The diagnosis of Zika virus infection is made by the association of epidemiological data, a compatible clinical picture, and confirmatory molecular and serological tests.

Diagnostic testing for Zika virus infection can be accomplished using both molecular and serologic methods. Laboratory testing can be performed by the Pan American Health Organization/World Health Organization (PAHO/WHO), the CDC Arboviral Diagnostic Laboratory, and some state health departments. In the United States, state health departments should be contacted to facilitate diagnostic testing for Zika virus. Laboratory specimens may also be sent to the CDC Arboviral Diagnostic Laboratory; instructions are available online at https://www.cdc.gov/zika/laboratories/test-specimens-bodyfluids.html. Communication should be initiated with the laboratory via telephone (1-970-221-6400) prior to shipment of specimens.

For a diagnostic workup, confirmation of evidence of Zika virus infection is needed. In recent infection, the nucleic acid amplification tests, particularly the real-time reverse-transcription polymerase chain reaction (rRT-PCR), detects viral genomic material in different body fluids (https://www.cdc.gov/zika/laboratories/types-of-tests.html). As time progresses since the acute infection in a suspected case, negative molecular tests are usual and must be followed by antibody tests. From the first 1 to 12 weeks (sometimes for months) of symptom onset, Zika virus IgM antibody test should be positive. Because cross-reactivity with other flaviviruses might occur and confound a positive result, a specific test for neutralizing antibody titers could help to confirm which flavivirus is involved. Nevertheless, facilities to perform a neutralizing antibody test are scarce, and the accuracy of this test is low.

The diagnosis of Zika virus can be made in serum, urine, and whole blood. Serum and urine are the primary diagnostic specimens, and whole blood is mainly used for nucleic acid assays. Some data suggest that Zika virus RNA may persist longer in urine and whole blood than in serum (76). Cerebrospinal fluid can also be used to diagnose neurologic complications of Zika; however, the absence of a positive PCR or IgM does not exclude the diagnosis of a postinfectious complication.

Diagnosis of Zika virus should be suspected in individuals with typical clinical manifestations and relevant epidemiologic exposure. The approach to diagnosis may vary depending on available resources and needs to be tailored to local circumstances. On the CDC website, one can find a detailed explanation of the specific situations in which testing for Zika virus infection should be requested: https://www.cdc.gov/zika/hc-providers/testing-guidance.html.

The duration of PCR positivity in babies congenitally infected with Zika virus can vary. According to the CDC, Zika virus RT-PCR testing should be performed on serum specimens collected from the umbilical cord or directly from the infant within 2 days of birth. A positive infant serum or urine rRT-PCR test result confirms congenital Zika virus infection. However, the duration of PCR positivity in infants can vary, and the sensitivity of serum detection assays (IgM and PCR) in identifying Zika infection declines after 3 months of age. A study reported that positivity declines to 33% after 3 months, and some children were PCR-positive beyond 200 days of life (13). Therefore, the duration of PCR positivity in congenitally infected babies can extend beyond the first few months of life. It is important to follow specific guidelines and recommendations from health authorities and medical professionals for accurate testing and management of congenitally infected infants.

In summary:

	• For individuals presenting with 7 or fewer days of symptoms, rRT-PCR of serum, whole blood, and urine tests should be performed. Any positive result establishes a definitive diagnosis. Because a negative result does not exclude the diagnosis, it should be complemented by serologic testing (Zika virus IgM and Plague Reduction Neutralization Test [PRNT]).
	• For individuals presenting after more than 7 days of symptoms, diagnosis of Zika virus should be based on serologic testing (Zika virus IgM and PRNT) (72).

The investigation of suspected cases of Zika virus neurologic complications follows the same principles of the general neurologic investigation and depends on the neurologic condition presented by the patient. In the face of microcephaly, genetic tests, amino acid and organic acid analysis, neuroimaging (tomography or, ideally, MRI), and TORCHS (Toxoplasmosis, HIV, Varicella, Parvovirus, Rubella, Cytomegalovirus, Herpes simplex, and Syphilis) screening should be ordered. In cases of Guillain-Barré syndrome, electromyography and nerve conduction studies, and CSF analysis are always helpful. If meningitis, encephalomyelitis, or transverse myelitis are suspected, neuroimaging (MRI) and CSF tests can be beneficial.

Management

	• Local or national health authorities should be notified of all suspected cases of Zika virus infection.
	• Because there is no specific treatment for Zika virus, the mainstay of therapy is symptomatic.
	• Treatment of Z-GBS is basically the same as for other causes of Guillain-Barré syndrome.

Zika virus disease is a nationally notifiable condition in the United States and other countries. Healthcare providers should report suspected Zika virus disease cases to their state, local, or territorial health department to facilitate diagnosis and mitigate the risk of local transmission. In the United States, state, local, and territorial health departments should report laboratory-confirmed and probable cases to the CDC (https://www.cdc.gov/pregnancy/zika/testing-follow-up/index.html). There is no specific treatment for acute Zika virus infection. Therapy is symptomatic with rest and adequate hydration. In cases of pain and fever, nonsteroidal anti-inflammatory drugs should be avoided, particularly in areas endemic to the dengue virus due to the risk of hemorrhagic complications. In such cases, acetaminophen is preferred.

The treatment of Z-GBS is the same used for idiopathic Guillain-Barré syndrome or for Guillain-Barré syndrome associated with other etiologies. Strategies vary according to the severity of the case and may range from symptomatic treatment to the use of intravenous gammaglobulin or plasmapheresis (for more details please refer to the article titled Acute inflammatory demyelinating polyradiculoneuropathy).

Outcomes

Acute Zika virus infection is a benign disease in the vast majority of cases. Z-GBS follows the same outcome of Guillain-Barré syndrome not associated with Zika virus with a good prospect of recovery in the long term. Congenital Zika syndrome has a poor prognosis with severe and permanent neurologic sequelae.

Special considerations

Pregnancy

The CDC recommends that pregnant women should not travel to areas with a Zika outbreak. Before traveling to other areas with risk of Zika virus, pregnant women should discuss their travel plans with their healthcare provider and carefully consider the risks and possible consequences of travel to these areas. If a pregnant woman must travel to one of these areas, she should be counseled to strictly follow steps to avoid mosquito bites and to prevent sexual transmission of Zika virus during and after the trip (https://wwwnc.cdc.gov/travel/diseases/zika#pregnant).

Anesthesia

Patients with Guillain-Barré syndrome are known to be sensitive to succinylcholine, muscle relaxants, and local anesthetics. Epidural and spinal anesthesia should also be used with caution (37).

Fentanyl seems to be the drug of choice for patients with microcephaly, and smaller doses per kg of weight are usually sufficient (77).