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    Zika: A report from the front lines

     

    Prevention

    The best way to prevent Zika infections is to avoid mosquito bites. The Centers for Disease Control (CDC) recommends that pregnant women not travel to areas with active Zika virus transmission and that those who must or who reside in such areas “strictly follow steps to prevent mosquito bites.”8 These include using a mosquito repellent containing DEET or picaridin and wearing permethrin-treated clothing with long sleeves and pants, socks and shoes to keep as much skin covered as possible. As the relevant mosquitoes (Aedes aegypti and Aedes albopictus) are daytime biters, minimizing outdoor activity from dawn to dusk would also be beneficial as would staying indoors in air-conditioned facilities. Also, at-risk women should ensure that screened enclosures have no openings or defects and that standing water near the house is eliminated to reduce mosquito breeding locations.

    Pregnant women whose male partners have traveled to or live in an area with active Zika virus transmission should minimize risk of infection by having their partner use condoms throughout the duration of the pregnancy.

    Couples considering pregnancy in the near future or who are actively trying to conceive should be discouraged from travelling to areas with ongoing transmission. Moreover, if they must travel to such areas, it is recommended that upon returning, they delay pregnancy attempts for 8 weeks if neither member of the couple is symptomatic with Zika, at least 8 weeks if only the woman is symptomatic, and 6 months if the man is symptomatic because Zika virus has been found in semen for up to 6 months. Women living in areas of active transmission or who frequently travel to such areas and who are not planning pregnancy should use long-acting reversible contraception (LARC).

    Early detection

    Much remains to be discovered about the optimal strategies for early detection and management of Zika infections in pregnant women and we are currently dependent on expert opinion leavened with early case series and epidemiologic data. Here are my recommendations:

    1. For ob/gyns who practice in areas without documented local mosquito-borne Zika transmission, the CDC recommends that patients be queried at each prenatal visit for possible exposure related to travel to areas with known Zika outbreaks or a history of unprotected sex with someone residing in or traveling to such areas or who was diagnosed with an infection.8

    It is also possible that contact with other bodily secretions of an infected person may cause transmission, as was apparently the case for a family caregiver of an elderly patient with a very high Zika viral load.9 If this exposure history is positive, inquire about possible Zika-related signs and symptoms (ie, nonpurulent conjunctivitis, maculopapular rash, arthralgia of small joints in the hands and feet, and fever).

    A. Symptomatic Patients:

    Estimate time from clinical presentation and: 

    i. If < 2 weeks, order serum and urine real-time reverse transcription-polymerase chain reaction (rRT-PCR) testing for Zika RNA. A positive result confirms an infection. A negative result should prompt an immediate order for IgM antibody tests for both Zika and dengue. Given a positive or equivocal Zika or dengue virus IgM result, next assess a plaque reduction neutralization test (PRNT). A negative (< 10) Zika virus PRNT indicates no Zika virus infection. A positive (≥10) PRNT titer for Zika virus together with a negative (<10) PRNT titer for dengue virus should be treated as confirmation of Zika infection.

    However, preliminary data indicate that PRNT might not consistently discriminate between Zika and other flaviviruses in patients with prior infections by, or vaccinations for, other flaviviruses (ie, dengue, West Nile, Japanese encephalitis, and yellow fever viruses) since a new infection enhances previously established flavivirus immune responses.10 Thus, if both the Zika and dengue virus PRNT values are ≥10, there is evidence of a nonspecific flavivirus infection. In this case, I would presume a possible Zika infection and begin ultrasound surveillance. These tests should be available from your state department of health, the CDC, and increasingly, commercial labs, although commercial labs’ fees may not be reimbursable.

    ii. If 2 to 12 weeks, order IgM for Zika and dengue. Negative IgM results for both viruses indicate no recent infection has occurred. If the Zika IgM is positive or equivocal, order reflex rRT-PCR on the same serum sample. I also recommend sending a urine sample for rRT-PCR to maximize sensitivity. Again the presence of viral RNA confirms the diagnosis. However, if the Zika IgM is negative but the dengue IgM is positive or equivocal, or if the Zika IgM was positive but the rRT-PCR was negative, order PRNT. A positive (≥10) PRNT titer for Zika and negative (<10) PRNT for dengue should also be considered diagnostic of infection as noted above.

     

    Charles J. Lockwood, MD, MHCM
    Dr. Lockwood, Editor-in-Chief, is Dean of the Morsani College of Medicine and Senior Vice President of USF Health, University of South ...

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