For health professionals: Zika virus

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What health professionals need to know about Zika virus

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

There are at least 2 Zika virus lineages which are the:

  1. Asian lineage
  2. African lineage

A recent research study suggests there may be three geographically distinct viral lineages (African I and II, and Asian), however much is still unknown about the evolution and diversity of Zika virus. The Asian lineage strain has recently emerged in the Pacific and the Americas.

Aedes aegypti is the primary vector of ZIKV. This species is largely restricted to tropical and subtropical regions, though temperate populations may occur in isolated refuges. Ae. albopictus has been implicated as a vector, though its role in the current outbreak is uncertain. This species is widely distributed outside the tropics, but is not known to be established in Canada. These species are notably the same type of mosquito that can carry dengue virus and chikungunya virus.

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

The incubation period ranges from 3 to 12 days. The 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 is growing scientific consensus that ZIKV infection during pregnancy can lead to Congenital Zika Syndrome, which includes a range of neurological and other developmental deficits including microcephaly and Guillain-Barré syndrome (GBS), and other congenital brain abnormalities.

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

Testing and Diagnosis

A clinician's decision to offer ZIKV testing is dependent on several factors:

  • pregnancy status
  • places and dates of travel
  • presence of symptoms consistent with Zika virus infection

Note: The current testing approach is based on our current understanding of the disease.

Decision-tree for Zika Virus Laboratory Testing

Infants and Children: The workup for potential Zika virus infection in pediatric patients, particularly in infants born to mothers affected in pregnancy, can involve some additional non-laboratory testing.

Please refer to the Canadian Paediatric Society, Practice Point, Dec 19, 2016 for guidance.

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Decision-Tree for Zika Virus Laboratory Testing

This image is a decision-tree intended to facilitate decision making with respect to Zika virus laboratory testing. Decisions to test should take into consideration populations at risk, travel history, possible non-travel related exposures (eg. sexual transmission) and presence of symptoms consistent with Zika virus infection. The choice of the optimal test including timing and modality are explained under the diagnostics section of the website.

The first question relates to the risk population. Is the patient male or female?

If the patient is male or non-pregnant female, do they have a Travel History or Sexual Partner with a Travel History to a country reporting local mosquito-borne transmission of Zika virus infection?

If the answer is “no”, testing for Zika virus infection is not recommended. Other infectious diseases with similar signs and symptoms are possible but Zika virus infection is unlikely in the absence of relevant travel or exposure history. Additional infectious diseases work-up may be warranted. If unsure about appropriateness or scope of work up, consider consultation with appropriate specialist.

If the answer regarding Travel History for the male or non-pregnant female is “yes”, please choose from the following options: “The patient is experiencing acute symptoms consistent with Zika Virus infection”, “The patient was previously symptomatic consistent with Zika virus infection and the symptoms have now resolved”, or “Symptoms consistent with Zika virus infection are absent”.

If the answer regarding Travel History for the male or non-pregnant female is “yes” AND if the patient is experiencing acute symptoms consistent with Zika virus infection, testing is recommended.

If the answer regarding Travel History for the male or non-pregnant female is “yes” AND if the patient was previously symptomatic consistent with Zika virus infection and the symptoms have now resolved, testing should be considered if a confirmed diagnosis would be helpful. Some scenarios, such as couples trying to conceive where pregnancy cannot be delayed for medical reasons, may warrant testing in situations where testing would not otherwise be warranted. Appropriate consultation with a specialist is recommended.

If the answer regarding Travel History for the male or non-pregnant female is “yes” AND if the patient has had no symptoms consistent with a Zika virus infection, testing is not routinely recommended. As with the previous example, some scenarios may warrant testing. Scenarios, such as couples trying to conceive where pregnancy cannot be delayed for medical reasons, may warrant testing in situations where testing would not otherwise be warranted. Appropriate consultation with a specialist is recommended.

If the patient is pregnant female, does she have Travel History or Sexual Partner with Travel History to a country reporting local mosquito-borne transmission of Zika virus infection?

If the answer is “no”, THEN testing for Zika virus infection is not recommended. Other infectious diseases with similar signs and symptoms are possible but Zika virus infection is unlikely in the absence of relevant travel or exposure history. Additional infectious diseases work-up may be warranted. If unsure about appropriateness or scope of work up, consider consultation with appropriate specialist.

If the patient is pregnant female AND has a Travel History or Sexual Partner with Travel History to a country reporting local mosquito-borne transmission of Zika virus infection, THEN the recommended action is to test for Zika virus infection AND consultation with an infectious diseases specialist is recommended. The presence or absence of symptoms does not predict risk of congenital Zika syndrome. Testing of all pregnant women with an appropriate travel history is recommended. Due to the complexity of interpretation and timelines of pregnancy, early consultation with an appropriate specialist should be considered.

Diagnostics

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

  • viral genetic material (RNA)
  • virus-specific antibodies produced by the body

There are currently 2 testing methods available for detection of Zika virus:

  • polymerase chain reaction (PCR) testing: This test directly detects the genetic material of Zika virus. A positive result confirms the patient has a Zika virus infection.

The PCR assay is most effective when testing clinical specimens such as:

  • blood collected within 10 days of start of symptoms
  • urine collected within 14 days of start of symptoms

The major limitation of this test is that Zika virus may only be present in these types of specimens for a short time after the start of an infection.

  • serology testing: Instead of testing for components of the virus, these tests look for Zika virus antibodies. Antibodies become detectable approximately one week post symptom onset.

The major advantage of a serology test is that it remains positive for several months or longer after infection.

The major limitations are that:

  • it is slow to perform
  • it is prone to cross-react with antibodies that target other similar flaviruses related to Zika virus, including the dengue virus. A positive result may in fact represent a previous exposure to another virus or past vaccination such as yellow fever, making interpretation difficult.

Testing Considerations

PCR and serology tests, if positive, can be used to confirm a Zika virus infection.

PCR

A positive PCR test for Zika virus signifies an acute infection despite mild symptoms that last for 2 to 7 days.

A negative PCR test for Zika virus may mean:

  • there was no infection
  • that the individual was infected but the virus was no longer present when the sample was collected. Subsequent serological testing is recommended.

If the PCR test result is negative, it may be that only the serology tests can confirm a case.

Serology

An initial positive serological result may represent:

  • an acute infection or previous exposure to Zika virus
  • an acute infection or previous exposure to another flavivirus
  • past vaccination, such as a yellow fever vaccine

The identification and confirmation of Zika virus-specific antibodies in serum samples may require further testing and in some cases collection of additional samples. This is due to possible cross-reactivity of serologic tests with antibodies that relate to other similar flaviviruses such as dengue virus.

A negative serological test for Zika could mean:

  • antibodies have yet to develop
  • there was no infection, which may warrant the collection of additional samples

A negative serology test performed one to two months following return from travel would indicate that there was no infection, since antibodies usually develop within four weeks following exposure. If the health care provider suspects the test was performed too early, a second blood sample may be collected for additional testing.

Patients should be aware and accepting of these test limitations and that results may not be available for a number of weeks.

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 cases of Zika virus infection. The Public Health Agency of Canada and provincial and territorial partners are working closely together to conduct national surveillance on Zika virus cases in Canada in response to this international outbreak. Health professionals who have questions about follow up in their jurisdiction should contact their local public health authorities for further details.

The National Microbiology Laboratory is able to detect the virus and offers testing support to provinces and territories. Some provincial laboratories also offer testing.

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

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