IDCM Issue 9: The Evolving Science of Zika Virus

Post Date: 
Natasha Chida, MD, MSPH

New Information on ZIKV Transmission. In April we reported that ZIKV is transmitted in 3 ways: through bites from infected mosquitoes, through sexual contact, and transplacentally. Recently, the possibility has been raised of ZIKV transmission through contact with sweat and tears.1  In Salt Lake City, Utah, a contact of a man infected with ZIKV (who had a very high viral load of 2.0X108 copies/ml,) developed ZIKV infection. The contact had helped reposition the patient and had wiped his eyes; there was no mucous membrane exposure. He had neither traveled to an area with circulating ZIKV, nor had intercourse with a person who had traveled to an area with ZIKV. Transmission through a mosquito bite was unlikely, because the Aedes mosquito species is not found where transmission occurred. Therefore, it is thought the route of transmission may have been the index patient’s sweat and tears.


What we know about sexual transmission of ZIKV has also evolved. It was first thought that sexual transmission occurred only via men who had symptoms. However, in June the first possible case of sexual transmission between a man with no symptoms and a woman occurred in Brittany, France.2 In addition, in July, the first case of a woman passing ZIKV to her male partner was documented in New York City. In this case ZIKV was found in the woman’s vaginal fluids and cervical mucus.2

New Guidance on Prevention of Sexual Transmission of ZIKV. In response to new information about sexually transmitted ZIKV, the World Health Organization now recommends that both men and women practice safe sex for 6 months after returning from an area where ZIKV is circulating (even if they have no symptoms).2 Prior guidance stated that only men needed to practice safe sex, and for a period of 2 months. The new advice is based on a case study that showed a man with ZIKV still had virus in his semen 188 days after symptom onset. In addition, in September the CDC recommended that all men with possible ZIKV exposure wait at least 6 months after symptom onset (if symptomatic) or last possible virus exposure (if asymptomatic) to attempt to conceive. CDC also recommended women with possible exposure wait to conceive until at least 8 weeks after symptom onset (if symptomatic) or last possible virus exposure (if asymptomatic).3

New Travel Advisories. 70 countries/territories have reported evidence of mosquito-borne Zika virus transmission since 2007.4See WHO’s full list

  • 53 had their first reported outbreak from 2015 onward

  • 4 had possible endemic transmission/local mosquito-borne infections in 2016

  • 11 countries have reported person-to-person transmission since February 2016

  • 20 countries/territories have reported microcephaly/CNS malformations potentially associated with ZIKV

  • The 2016 Summer Olympics held in Rio de Janeiro ended in August. So far there have been no laboratory-confirmed cases of ZIKV for anyone associated with the Olympics.

  • The CDC recently advised that pregnant women should consider postponing nonessential travel to those Southeast Asian countries reporting (a) local transmission of ZIKV or (b) cases related to travel to those countries.5 CDC further advises postponing travel to bordering countries where limited information is available.

Diagnostic Testing for ZIKV. Serum and urine are the preferred specimens for laboratory diagnosis. CSF, amniotic fluid, and tissue specimens can also be tested. Several tests are currently available7:

  • The real-time reverse transcription-polymerase chain reaction (rRT-PCR)

    •  A positive rRT-PCR result on any sample confirms ZIKV infection

    • Due to the sensitivity of the test, a negative rRT-PCR result does not exclude ZIKV; and serum should be analyzed by IgM antibody testing.

    • Another PCR, the Trioplex rRT-PCR, exists. This tests can detect ZIKV, dengue, and chikungunya.

  • The Zika MAC-ELISA:

    • Can detect ZIKV IgM in serum or cerebrospinal fluid.

    • IgM levels of ZIKV are generally positive from 4 days post symptom onset and until 12 weeks.

    • There is cross-reaction with other flaviviruses; therefore, positive, equivocal, or inconclusive tests must have confirmation by plaque-reduction neutralization testing (PRNT).

    • The diagnostics currently being used take 2 days to complete. Recently, the US Department of Health and Human Service’s has awarded funding to a private company to create a test that returns a result in 4 hours.6

  • Up to date testing recommendations are available from CDC 7


Potential Link Between ZIKV and Guillain-Barré Syndrome (GBS). Guillain-Barré Syndrome occurs when the body's immune system attacks the myelin of the peripheral nervous system.8 It can occur after infections. Recent findings from a study conducted in Puerto Rico support an etiologic association between ZIKV (or other flavivirus infections) and GBS.9 In February 2016, the Puerto Rico Department of Health and CDC began to monitor the incidence of GBS. Between January and July, 56 patients developed GBS; 34 (61%) had recent ZIKV (or other flavivirus) infection; the patients were all adults. This incidence of GBS associated with ZIKV/other flavivurses was 2.5 times the GBS incidence not associated with viral infections. The most common antecedent symptoms in patients with GBS associated with a virus were rash (53%), fever (35%), and diarrhea (21%). The most common GBS symptoms were hypo/areflexia (97%), leg weakness (97%), leg paresthesia (75%), arm weakness (75%), facial weakness (63%), arm numbness (59%), and dysphagia (59%). The median interval between infection symptoms and GBS was 5 days. Of note, this was a case-control study; no prospective cohort studies have been done, so we do not yet know what the incidence of GBS is in patients with ZIKV.



  1. Swaminathan S, et al. Fatal Zika Virus Infection with Secondary Nonsexual Transmission. N Engl J Med. 2016. PMID: 27681699

  2. World Health Organization. Prevention of sexual transmission of Zika virus. Interim guidance update. 2016. Accessed 10/11/16. Available at:

  3. Petersen EE, et al. Update: Interim Guidance for Preconception Counseling and Prevention of Sexual Transmission of Zika Virus for Persons with Possible Zika Virus Exposure — United States, September 2016. MMWR Morb Mortal Wkly Rep. 2016;65(39):1077-1081. PMID: 27711033

  4. World Health Organization. Zika situation report.  2016. Accessed 10/11/16. Available at:

  5. Centers for Disease Control and Prevention. Zika Virus in Southeast Asia. 2016. Accessed 10/11/16. Available at:

  6. Abbasi J. Zika Vaccine Enters Clinical Trials. JAMA. 2016;316(12):1249. PMID: 27673295

  7. Centers for Disease Control and Prevention. Testing for Zika. 2016. Accessed 10/11/16. Available at:

  8. Willison HJ, et al. Guillain-Barré syndrome. Lancet. 2016;388(10045):717-27. PMID: 26948435

  9. Dirlikov E, et al. Guillain-Barré Syndrome During Ongoing Zika Virus Transmission — Puerto Rico, January 1–July 31, 2016. MMWR Morb Mortal Wkly Rep 2016;65:910–914. PMID: 27584942



The Johns Hopkins Center for Clinical Global Health Education is a clinical research, education, and leadership development center in the Division of Infectious Diseases, Department of Medicine, Johns Hopkins University School of Medicine. We conduct clinical research, and we train, support, and empower healthcare providers and researchers working in resource-limited communities who share our commitment to improve health outcomes.