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Zika Virus

Zika Virus is a viral illness primarily transmitted by mosquito bites.  Like dengue and chikungunya viruses, the most common mosquito vectors are Aedes aegypti and, to a lesser extent, Aedes albopictus. Both mosquito species prefer urban environments and are considered “day-biters,” although they are most active in the early mornings and evenings.
Unlike dengue and chikungunya, zika can also be transmitted through sex and can cause birth defects if infection occurs during pregnancy. Male-to-female sexual transmission occurs more commonly than female-to-male or male-to-male transmission. Transmission by an asymptomatic partner has been documented. Zika RNA persists in semen for a mean of approximately 54 days and is cleared within 81 days after symptom onset in 95% of patients. 
 
Prevention is mainly mosquito-bite avoidance, which is best accomplished by careful use of the DoD Insect Repellent System and Insect Repellent Treatment of Military Uniforms when traveling/deploying to areas with zika transmission.  Additionally, personnel should use condoms or abstain from sex for 2 months (females) or 3 months (males) after return from an area with zika transmission regardless of whether or not the traveler/deployer felt ill.  Women who are pregnant or planning to become pregnant should avoid travel to areas with zika. 
Current locations with zika can be found here: CDC Zika Map

 

Geographic Distribution:

Until 2007, case reports and serosurveys indicated sporadic zika infections limited to Africa and Asia.  In 2007, a large outbreak occurred in Yap, Micronesia.  Since then, outbreaks have been reported in 87 countries, including a large 2015-2017 outbreak in most of Latin America and the Caribbean.  Global cases have declined markedly since 2017, but evidence of viral circulation continues in Latin America, India, Southeast Asia, and Africa.  Surveillance is markedly incomplete due to mild, non-specific presentation and the high levels of asymptomatic cases.   
In the U.S., over 5,500 imported cases and two small outbreaks in the Southeastern U.S. have been reported, with cases peaking in 2016.  There have been no confirmed zika cases reported in the U.S. or its territories since 2019.
Current locations with known zika transmission can be found here: CDC Zika Map
 

Clinical features:

Zika has an incubation period of 3-14 days, with a median of 5 days.  Approximately 80% of infections are asymptomatic.  Clinical symptoms of zika are typically mild.  Fever occurs in approximately 50% of cases and lasts about a day.  Rash, itching, headache, joint and muscle pain, and conjunctivitis are all common. Illness typically lasts 4-7 days, and rarely results in serious or prolonged illness.  The high rate of asymptomatic infections and otherwise mild, non-specific illness result in difficulties with disease surveillance, with cases and small outbreaks are often undetected.  Complications can include Guillain-Barré syndrome (GBS) and rare cases of myelitis and meningoencephalitis.  CDC Clinician Page
Zika infection during pregnancy is strongly associated with congenital Zika syndrome.  Up to 7% of infections in pregnancy will result in fetal loss, and 5% to 14% will develop congenital Zika syndrome; a small percentage of newborns will develop more subtle symptoms that may not be detectable at birth.  Congenital Zika syndrome is characterized by microcephaly (4%–6%), decreased brain tissue and brain damage, ocular damage, joint defects (e.g. clubfoot), and poor tone.  More about Congenital Zika Syndrome:  CDC Congenital Zika
 

Diagnostic Testing

Diagnostic Testing in DoD can be performed at NIDDL (Sept 2023): ZIKA VIRUS-Dengue-Zika Testing
US CDC recommends testing for:
  • Symptomatic persons residing in or having recently traveled to a known zika virus risk area. Both RT-PCR and IgM testing should be offered.
  • Symptomatic persons who have had unprotected sex with a partner who resides in or who has recently traveled to a zika virus risk area.
  • Asymptomatic pregnant women with possible ongoing zika exposure (including those who reside in a zika risk area or have unprotected sex with a partner who resides in or has recently traveled to a zika risk area). These women should be offered Zika RT-PCR 3 times during pregnancy.
  • Asymptomatic pregnant women with possible recent zika virus exposure (e.g., recent travel to a zika risk area or sexual exposure). These women may desire RT-PCR and IgM testing, but US CDC recommends that such testing be undertaken only after informed discussion. IgM tests can produce false positive results in many settings and are unable to distinguish a previous infection that may have occurred prior to the pregnancy from an infection related to the current pregnancy.
  • Pregnant women with possible zika virus exposure who have a fetus with prenatal ultrasound findings consistent with Congenital Zika Syndrome.
For symptomatic pregnant women, both RT-PCR testing (serum or urine) and serum IgM testing for zika is indicated for up to 12 weeks after symptom onset.
 
Limitations of zika virus testing:
Cross-reactivity with other flaviviruses:  Positive IgM tests must be confirmed by using neutralization tests to rule out cross-reaction with related flaviviruses (e.g. dengue, Japanese encephalitis, West Nile and yellow fever viruses) and must be confirmed with neutralization testing.
Difficulty in determining time of exposure: Positive IgM tests may not always indicate a recent infection or whether a woman became infected before or after becoming pregnant. IgM results before pregnancy should not be used to determine whether it is safe for a woman to become pregnant. IgM testing before pregnancy may help to establish a baseline for determining whether a woman becomes infected during pregnancy.
Negative RT-PCR or IgM testing does not rule out infection.

Web Resources

Center for Disease Control and Prevention (CDC):  Zika Virus Main Page
Center for Disease Control and Prevention (CDC) “Yellow Book”, 2024: Zika Chapter
World Health Organization: Zika Virus Fact Sheet
 

Policy and Guidance

 

 

Mosquito Bite Avoidance-Vector Control

  • Apply 25-30% DEET or 20% picaridin based repellents on exposed skin and treat clothing with a permethrin-containing product.
  • Wear long-sleeved light-colored shirts and pants whenever outdoors or in places where mosquitoes may be present.
  • Reduce the number of breeding mosquitoes by removing water from any containers around buildings.
  • Limit vegetation around buildings to prevent overgrowth and potential mosquito harborages.
 

Reporting

Zika is a nationally notifiable disease.  BUMEDINST 6220.12C and NMCPHC-TM-PM 6220.12 require that all cases of Zika must be reported to Preventive Medicine authorities.  Notify your cognizant Navy Environmental and Preventive Medicine Unit (NEPMU) and state or local health department so that measures can be taken to mitigate the risk of local transmission. NEPMU staff can advise on and/or assist with case investigation activities, laboratory testing, and vector control measures. NMCFHPC Medical Surveillance and Reporting Resources
Case Classification per Armed Forces Medical Reportable Events Guide
Non-Congenital
Probable:
A case with ALL of the following:
  • Meets the exposure criteria* as described below and
  • Zika virus positive IgM antibody from serum or CSF with any of the following:
    • Dengue virus negative IgM antibody and no Zika virus PRNT test performed or
    • Positive PRNT titer against Zika and Dengue (or other flavivirus endemic to the region where exposure occurred)
 
Confirmed:
A case with any of the following:
  • Zika virus identified by culture from any acceptable clinical specimen or
  • Zika virus positive antigen from any acceptable clinical specimen or
  • Zika virus nucleic acid (RNA) detected (example: PCR, sequencing, NAAT) from any acceptable clinical specimen or
  • Zika virus positive IgM antibody from serum or CSF with a positive PRNT titer against Zika AND a negative PRNT titer against Dengue (or other flavivirus endemic to the region where exposure occurred).
 
Congenital
Probable:
A case with ALL of the following:
  • Mother meets the exposure criteria* described below or the laboratory criteria described above for Zika Virus Infection, Non-congenital and
  • Zika virus positive IgM antibody from neonatal serum or neonatal CSF collected within 2 days of birth with any of the following:
    • Dengue virus negative IgM antibody and no Zika virus PRNT test performed or
    • Positive PRNT titer against Zika and Dengue (or other flavivirus endemic to the region where exposure occurred)
 
Confirmed:
A case with any of the following:
  • Zika virus identified by culture from any acceptable neonatal clinical specimen within 2 days of birth or
  • Zika virus positive antigen from any acceptable neonatal clinical specimen within 2 days of birth or
  • Zika virus nucleic acid (RNA) detected (example: PCR, sequencing, NAAT) from any acceptable neonatal clinical specimen within 2 days of birth or
  • Zika virus positive IgM antibody from umbilical cord blood, neonatal serum, or neonatal CSF collected within 2 days of birth with a positive PRNT titer against Zika AND a negative PRNT titer against Dengue (or other flavivirus endemic to the region where exposure occurred).
 
*Exposure criteria is defined as:
  • Resides in or recent travel to an area with known zika virus transmission
  • Sexual contact with a ZIKA VIRUS case within the infection transmission timeframe
  • Sexual contact with a person with recent travel to an area with known zika virus transmission
  • Receipt of blood or blood products within 30 days of symptom onset
  • Organ or tissue transplant recipient within 30 days of symptom onset
  • Association in time and place with a zika case
  • Likely vector exposure in an area with potential for zika virus transmission
 
Critical Reporting Elements:  Type of disease (Non-Congenital or Congenital). Travel and/or deployment history during the incubation period, circumstances of exposure if known (e.g. duty, occupation, environmental factors).
 

Epidemiology and Publications

NMCFHPC- EpiData Center: *CAC required*   EDC Case Finding Disease Profile-Zika.pdf
AFHSD MSMR March 2023 Vol. 30 No. 3 Zika Virus Among Department of Defense Service Members and Beneficiaries, 2013-2022
AFHSD MSMR December 2016 Vol 23 No. 12 Zika virus infections in Military Health System beneficiaries since the introduction of the virus in the Western Hemisphere, 1 January 2016 through 30 November 2016
AFHSD MSMR July 2019 Vol 26 No. 7 Zika virus surveillance in active duty U.S. military and dependents through the Naval Infectious Diseases Diagnostic Laboratory
AFHSD MSMR Feb 2021 Vo1 28 No. 2  Surveillance for Vector Borne Diseases among AD, 2016-2020
Center for Disease Control and Prevention (CDC): Geography and epi of U.S. Cases  

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