For health professionals: Zika virus

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What health professionals need to know about Zika virus

Zika virus is primarily a mosquito-borne disease. It's a single stranded RNA Flavivirus from the Flaviviridae family.

There are 2 Zika virus lineages which are the:

  1. Asian lineage
  2. African lineage

The Asian lineage has recently emerged in the Pacific and the Americas.

Aedes aegypti and Aedes albopictus are the primary vector species transmitting Zika virus. These species are notably the same type of mosquito that can carry dengue virus and chikungunya virus.

Aedes aegypti is mainly restricted in its distribution to tropical and subtropical regions.

However, Aedes albopictusis a highly invasive species that has successfully colonized tropical, sub-tropical and temperate regions. It's now established on all continents except Antarctica.

Other Aedes species that may also be involved in transmission, where present, include Aedes:

  • hensilli
  • vittatus
  • africanus
  • unilineatus
  • polynesiensis
  • luteocephalus

Currently, the Aedes mosquitoes that transmit Zika virus are not established in Canada due to the climate. So, there is a very low probability of mosquito transmission in Canada.

Zika virus is related to:

  • yellow fever
  • West Nile virus
  • dengue viruses
  • St. Louis encephalitis
  • Japanese encephalitis

Familiarize yourself with the:

This enables you to include Zika virus in your differential diagnosis for travellers returning from countries with reported mosquito-borne cases.

Sexual transmission

There's increasing evidence about the role of sexual transmission of Zika virus. The rapid risk assessment provides the latest information on this topic.

Clinical manifestations

Asymptomatic infections are common. Only 1 in 4 people infected with Zika virus are believed to develop symptoms.

The main symptoms of Zika virus infection include:

  • maculopapular rash
    • often spreading from the face to the body
  • retro-orbital pain
  • low-grade fever (less than 38.5°C)
  • general non-specific symptoms, such as:
    • myalgia
    • asthenia
    • headaches
  • transient arthritis or arthralgia with possible joint swelling
    • mainly in the smaller joints of the hands and feet
  • conjunctival hyperaemia or bilateral non-purulent conjunctivitis

The incubation period ranges from 3 to 12 days. The disease symptoms are usually mild and last for 2 to 7 days. Most people recover fully without severe complications and require only simple supportive care. Hospitalization rates are low.

Infection may go unrecognized or be misdiagnosed as dengue, chikungunya or other viral infections causing fever and rash.

There have been some deaths reported from Zika virus infection. These were mostly from microcephaly and congenital abnormalities associated with Zika virus infection.

Experts now agree that Zika virus causes microcephaly and Guillain-Barré syndrome (GBS).

Microcephaly

According to the World Health Organization, microcephaly and other fetal malformations potentially associated with Zika virus infection or suggestive of congenital infection have been reported in 6 countries. These countries are:

  • Brazil
  • Panama
  • Colombia
  • Martinique
  • Cabo Verde
  • French Polynesia

Two additional cases, each linked to a stay in other countries reporting microcephaly, were detected in Slovenia and the U.S.

Guillain-Barré syndrome

A total of 13 countries and territories worldwide have reported an increased incidence of:

  • GBS and/or
  • laboratory confirmation of a Zika virus infection among GBS cases

Diagnosis

Preliminary diagnosis is based on the patient's:

  • clinical features
  • places and dates of travel
  • activities

Laboratory diagnosis is generally accomplished by testing serum or plasma to detect any of the following:

  • viral ribonucleic acid (RNA)
  • virus-specific IgM and neutralizing antibodies

Diagnostic tests for Zika virus infection include:

  • polymerase chain reaction (PCR) tests during acute illness to directly detect viral RNA
  • other tests to detect the specific antibody against Zika virus in serum

Zika virus may be present in detectable levels of a patient's blood for up to a week after symptom onset. However, it's recommended that a serum sample be taken during the first 5 days after the onset of symptoms. This is to enhance detection of viral RNA.

Presence of viral RNA in urine may extend up to 10 days or more after symptoms are noted. This may be considered as an alternative or additional sample for PCR testing.

Serum samples collected after 7 days can be tested for the presence of Zika virus antibody. Case confirmation involving samples taken a week or more after symptom onset may require serological testing, such as the detection of:

  • IgM antibody
  • neutralization antibodies specific for the virus

Identification and confirmation of Zika virus specific antibody in serum samples can, at times, be problematic. This is due to the cross-reactivity of diagnostic Flavivirus antibody assays. This is particularly the case if the patient was previously infected with a related Flavivirus, such as dengue.

Testing scenarios

Testing for Zika virus infection should be considered in the diagnosis of any ill traveller:

  • with underlying medical conditions
  • with compatible epidemiologic and clinical history
  • who develops more serious symptoms that could be consistent with Zika virus infection
  • who visited an area where Zika virus transmission is ongoing or widespread and has symptom onset:
    • within 3 days after arrival
    • up to 14 days after departing

Testing for other similar viral infections and for malaria should also be done as appropriate.

Testing is generally not warranted for returned travellers:

  • who've travelled and remain asymptomatic
  • whose clinically compatible illness has resolved

This is because of the currently limited availability of laboratory testing and uncertain benefit of such testing. Considering the cases of neurologic disorders reported following Zika virus infection, returning travellers should report any neurologic symptoms.

In the event of the diagnosis of GBS or other unusual neurologic syndromes, a travel history should be elicited. If Zika virus infection is thought to be potentially associated with the illness, a specialist should be consulted.

Testing should be offered to pregnant women with:

  • a fetus suspected of having a congenital anomaly
  • acute signs and symptoms compatible with Zika virus
  • a clinical history of a compatible Zika virus-like illness, either during or after travel to an area with Zika virus transmission

Testing of pregnant returning travellers who are asymptomatic should be discussed between the woman and her health care provider. In these discussions, it's important to consider:

  • overall test result interpretation
  • current diagnostic testing problems, including:
    • sensitivity
    • specificity
  • the prolonged turnaround time of the available tests, which may be problematic in some cases

The decision to test should also include consideration of how the results will be used to inform subsequent decisions.

Treatment

Currently, there is no prophylaxis, vaccine or treatment for Zika virus. Treatment may be directed toward symptom relief, such as:

  • rest
  • fluids
  • analgesics
    • avoid acetylsalicylic acid (ASA) and other nonsteroidal anti-inflammatory drugs until dengue infection has been eliminated as a possibility
  • antipyretics

Surveillance in Canada

Health professionals in Canada play a critical role in identifying and reporting cases of Zika virus infection. You must report to your local public health authority, as per reporting legislation and/or regulations within your jurisdiction.

The National Microbiology Laboratory is able to detect the virus and offers testing support to provinces and territories.

You can find more information in the Zika virus surveillance section.

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