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 is a single stranded RNA Flavivirus from the Flaviviridae family.

There are 2 Zika virus lineages which are the:

  1. African lineage
  2. Asian 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 chikunguyna virus.

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

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

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

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

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:

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

Familiarize yourself with the:

Also, this is so you can include Zika virus infection in your differential diagnosis for travellers returning from countries with reported locally acquired Zika virus.

Sexual transmission

There is 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 disease include:

  • low-grade fever (less than 38.5°C)
  • maculo-papular rash
    • often spreading from the face to the body
  • 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
  • retro-orbital pain
  • general non-specific symptoms, such as:
    • myalgia
    • asthenia
    • headaches

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.

During 2015 and 2016, 8 countries and territories have reported an increased incidence of Guillain-Barré syndrome (GBS). This includes laboratory confirmation of a Zika virus infection among GBS cases.

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

In October 2015, an investigation was prompted in the State of Pernambuco, Brazil. This was due to reports of an unusual increase of cases of microcephaly (abnormally small head) among newborns.

As of March 9, 2016, Brazil's Ministry of Health:

  • reported 6,158 suspected cases of microcephaly or other nervous system malformations among newborns since October 2015
  • investigated 1,927 cases and identified 745 confirmed cases of microcephaly and/or other central nervous system malformations
  • ruled out 1,182 suspected microcephaly cases
  • continues to investigate 4,231 reported microcephaly cases

This contrasts with the period from 2001 to 2014, with Brazil recording an average of 163 microcephaly cases annually.

More information can be found at:

To date, an increase in cases of microcephaly and other neonatal malformations have been reported by Brazil and French Polynesia. Monitoring of pregnant women in other countries experiencing Zika virus outbreaks is ongoing.

Experts now agree that Zika virus causes both microcephaly and GBS.

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:

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

Diagnostic tests for Zika virus infection include:

  • PCR tests during acute illness to directly detect viral RNA
  • other tests to detect 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 is 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. They 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 compatible epidemiologic and clinical history
  • with underlying medical conditions
  • who develops more serious symptoms that could be consistent with Zika virus infection
  • who visited a country 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:

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

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 Guillain-Barré syndrome 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:

  • 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
  • a fetus suspected of having a congenital anomaly

Testing of pregnant returning travellers who are asymptomatic should be discussed between the woman and her health care provider. In these discussions, it is 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
  • antipyretics
  • analgesics
    • avoid acetylsalicylic acid and other nonsteroidal anti-inflammatory drugs until dengue infection has been eliminated as a possibility

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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