Understanding of sexual transmission of Zika virus is based on data from a limited number of cases. To prevent the spread of Zika virus through sex, animal and human models are needed to understand how the virus is transmitted through body fluids and how long it persists.

Prof. Johan Neyts, University of Leuven"Besides the transmission via mosquitoes, Zika can also be vertically transmitted from mother to unborn child and via the sexual route. Here we will study in more detail both the vertical and sexual transmission route, to this end appropriate models will be used or newly established."

Prof. Johan Neyts, University of Leuven (KU Leuven)

Overall Objectives

The aim of the group is to investigate the extent of and factors associated with sexual transmission of Zika virus (ZIKV) in human and animal models.

Specific Objectives

  • Establish an ex vivo model of human female genital tract for Zika virus sexual transmission,
  • Study whether an infected foetus contributes to viremia in the mother (mouse models),
  • Establish a mouse model of vertical transmission,
  • Assess the frequency and kinetics of Zika virus (ZIKV) persistence in semen samples by means of RT-PCR,
  • Assess replication fitness of ZIKV in semen, by isolation of ZIKV virions in culture,
  • Evaluate early target cells in ex vivo human tissue models of sexual transmission.
  • Establish the potential for sexual transmission of Zika virus by viral persistence in semen of returned travelers with confirmed Zika virus infection.

Results and Achievements

KU Leuven (KUL) (group leader) has established a mouse model to assess Zika virus replication in the testicles and to study the efficacy of antivirals on viral levels in this organ. The effect of compounds that show efficacy in this model can next be in vertical/sexual transmission models. This will be essential to the development of specific therapeutic interventions or prophylactic treatment to mitigate or even prevent severe complications of Zika infections.

The finding of ZIKV persistence in semen and its associated potential for sexual transmission hascaused great concern among persons of child-bearing age who were exposed to ZIKV infection. The Institute of Tropical Medicine in Antwerp (ITG) conducteda prospective observational study in which travelers returning from endemic regions with confirmed ZIKV infection were recruited and sequential semen samples were collected for each case.

This study revealed that more than half of the ZIKV-infected men had prolonged shedding of ZIKV in the semen, for a median duration of 83 days (maximum 144). Isolation of ZIKV from semen was successful in one case only, collected at 11 days post symptom onset. The potential for sexual transmission cannot be excluded as long as ZIKV RNA is detected in semen.

To further explore the mechanism of sexual transmission of ZIKV, an ex vivo human tissue model of the cervix and uterus has now been developed and characterized. Studies of ZIKV infection in the female genital tract are ongoing, using five ZIKV isolates that were obtained from patient’s semen samples (4 isolates) and from serum (1 isolate). The isolates were sequenced and made available to other consortium members. This ex vivo model is also important to assess the efficacy of potential therapeutic agents in blocking ZIKV entry into target cells.

Participating Organisations

Group leader: Prof. Johan Neyts, University of Leuven (KU Leuven)

  • Institute of Tropical Medicine in Antwerp
  • Schweizerisches Tropen- und Public Health-Institut