Zika Clinical Manifestations

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The page below is a sample from the LabCE course Mosquito-Borne Viral Diseases. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Zika Clinical Manifestations

Most cases of Zika are asymptomatic or mild. If there are symptoms, they seldom last more than a week. Most symptomatic individuals present with fever and rash, joint pain or conjunctivitis, muscle aches, and/or headache. The incubation period is estimated to be from a few days up to a week. Rarely is hospitalization needed or death reported. Once infected, a person is immune. Symptoms overlap with those of dengue fever and chikungunya infection. Laboratory testing must be performed to correctly identify the etiology of the illness.
Guillain-Barre syndrome has been reported in patients after Zika infection. Guillain-Barre syndrome is a rare disorder of muscle weakness and possible paralysis; a form of acute motor axonal neuropathy. Most people recover over time, but sometimes paralysis is permanent. The infected patient's own immune system attacks nerve cells. Sustained motor, low visual acuity, and cognitive decline were reported in a study of patients diagnosed with Zika virus in Brazil. Very rare cases of acute myelitis and meningoencephalitis have been reported in Zika-infected patients. Acute disseminated encephalomyelitis is seen much less than Guillain-Barre but has been reported in Brazil. It damages the white matter in the brain and may last six months after Zika infection. It is an immune-mediated disease characterized by demyelination and polyfocal neurologic symptoms. Animal studies have shown that adult brain cells can be destroyed.
The greatest risk of infection with Zika occurs if a pregnant patient is infected. The earlier in the pregnancy the patient is infected, the greater the likelihood of damage to the fetus. Pregnancy can end in miscarriage or stillbirth, or the child may be born with severe neurological damage. The worst of this is microcephaly. Infants with microcephaly have much smaller heads than normal because their brain is damaged or stopped growing. Symptoms of microcephaly include seizures, developmental delay, intellectual disability, ocular abnormalities, hearing loss, movement disorders, and difficulty feeding. The Zika virus has been identified in the amniotic fluid, placental, and brain tissue of babies with microcephaly. Other infections, such as cytomegalovirus (CMV) or rubella virus infection, in pregnant patients can also cause microcephaly.
Arthrogryposis (joint contractures) has also been reported in infants born with the Zika virus. Musculoskeletal deformities secondary to neurological abnormalities are seen in the arms and legs. These infants also had malformations and calcifications in the cortex of the brain, as well as decreased brain volume and hypoplasia of the brainstem and cerebellum.
A study in Thailand of patients with laboratory-confirmed dengue virus antibodies who were then infected with Zika were more likely to have a higher viral load, more severe disease, and possibly greater susceptibility to Zika virus. This has implications for more congenital infections and neurological sequelae.
There is no specific antiviral treatment and no vaccine at this time.

Figure 22. Comparison of typical head size to microcephaly