Updated Zika Virus Testing from SDCL

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Updated Zika Virus Testing

Zika virus infection is caused by a flavivirus transmitted through the bite of an infected Aedes mosquito, mainly Aedes aegypti. Although infections in humans were documented in the 1950s, Zika virus has only recently emerged as a disease of significant public health concern. At the time of writing, a large outbreak in the Americas has affected more than 20 countries. Before these outbreaks, known areas of endemic transmission were limited to Asia and Africa. It is likely the virus will continue to spread because the principle vectors are found in many tropical and subtroptical regions as well as in some warmer temperate regions.

Currently, the significant and emerging concern about Zika virus is the spatial and temporal clustering of the Zika virus outbreak in Brazil with the increase in the incidence of children born with microcephaly. This association has been supported in a small number of cases, through detection of Zika virus genome in amniotic fluid, placenta and tissues of affected fetuses and neonates. In addition, an apparent increase in Guillain-Barré syndrome has been noted in Zika virus affected areas of Brazil, and El Salvador, and previously in French Polynesia.

The recommended screening for women with two or more symptoms consistent with Zika virus (including acute onset of fever, maculopapular rash, arthralgia or conjunctivitis) who have returned from a Zika virus endemic area is:

  • Serum as primary specimen, 5 ml collected serum separator vacutainer (SST), centrifuged, within 10 days of onset of symptoms,
  • Random urine can be added as a secondary sample, 20 ml in sterile container, submitted on an ice pack, collected within 10 days of onset of symptoms

The samples are submitted to the National Microbiology Laboratory for Zika virus PCR. IgM serology will be performed on all PCR-negative serum samples.

Zika virus serology cross reacts with West Nile virus, dengue and yellow fever, therefore positive results will be resolved by further evaluation using PRNT (plaque-reduction neutralization test). The PRNT is a technically complicated test which requires at least one week incubation. Confirmation of Zika virus infection by serology often requires a convalescent sample taken 2-4 weeks after the acute illness.

For each sample you must include:

  • Symptoms, and date of onset of symptoms
  • Date sample taken
  • Travel history, including travel dates to known dengue- and Zika-affected areas.

The NML will test asymptomatic patients. There are challenges in interpreting serology results of asymptomatic pregnant women who have returned from an area where Zika virus is known or suspected to be circulating:

  1. When to test in order to reliably predict the detection of antibodies is determined by: from the date of last potential exposure (return to Canada), add 14 days for incubation period, plus one week viremia plus one week for the appearance IgM,or test one month after the individual has returned from her trip. This will ensure one does not miss a seroconversion (false negative) and provide the patient with misinformation about being exposed to the virus.
  2. The performance characteristics of the assay are not known, that is, at this time we do not know what the sensitivity and specificity of the test means with respect to risk for sequelae such as microcephaly.

Because of the limitations on interpreting serology, clinicians should consider serial ultra sounds (every 3-4 weeks) to follow pregnant women with confirmed or suspected (if testing results are pending) Zika virus infection in pregnancy or for asymptomatic pregnant travelers returning from Zika virus infected areas. Any results that are concerning should prompt consultation with a specialist such as a Maternal Fetal Medicine Specialist to help define risk and counsel the mother.

In summary, consider testing pregnant women (symptomatic and asymptomatic) who have returned from an area where Zika virus is known or suspected to be circulating. Also consider Zika virus when investigating Guillian-Barré syndrome, fetal loss or sickle cell crisis if there is a travel history.

For additional information on Zika virus for health please see CATMAT guidance on PHAC website:

http://healthycanadians.gc.ca/publications/diseases-conditions-maladies-affections/committee-statement-treatment-prevention-zika-declaration-comite-traitement-prevention/index-eng.php?id=zika_virus_16_phac_catmat

If you require further information on Zika virus testing please call SDCL microbiologist on-call at 306-798-1234.

Prepared by Greg Horsman, Medical Director, SDCL

Zika Virus Q&A (from the Department of Family Medicine Meeting October 2016)

  1. Who should be screened this was copied and pasted from the SDCL guidelines (website below):

 Patients for recommended screening:

(A) Testing is recommended for currently symptomatic patients with illness compatible with acute Zika virus infection within 14 days of symptom onset.

(B) Testing is recommended for asymptomatic pregnant patients. Submit serum as well as urine sample for PCR and serology collected within 14 days of departure from an endemic or currently affected area. Also, submit a serum for serology 30 days after departure from an endemic or currently affected area.”

Laboratory Testing:

  1. On the question of wait time for conceiving etc – this was copied and pasted from the PHAC website below:
  • Pregnant women and their male partner

If travel to a risk area (http://www.healthycanadians.gc.ca/ diseases-conditions-maladies-affections/disease-maladie/ zika-virus/risks-countries-pays-risques-eng.php) is unavoidable, pregnant woman and male partners should practise abstinence or use condoms until more is known about the prolonged viral shedding of ZIKV in semen. If the male partner of pregnant female has been in a risk area the couple should practise abstinence or use condoms for the full duration of the pregnancy (including after return).

  • Couples planning a pregnancy

Based on current information on the incubation period and duration of viremia, and the unclear duration of viral persistence in tissues, women planning a pregnancy should wait at leasttwo months after their return from an area of risk before trying to conceive. For couples where the male partner has travelled in an area of risk, it is reasonable to delay trying to conceive forsix months.

  • Couples outside the context of current or planned pregnancy

Men who have returned from a risk area and who wish to reduce the possibility of sexual transmission to their partner (outside of the context of pregnancy) can do so through appropriate use of condoms. Although transmission has so far only been reported after symptomatic infection, and it is plausible that the risk after asymptomatic infection is lower, there are no data to support making different recommendations for symptomatic or asymptomatic men. Use of condoms likely provides the greatest protection in the first weeks following illness, but given the potential for long-term persistence in semen, condom use should be considered for six months after return from a risk area.

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