Study confirms that the Zika virus can be transmitted sexually.

Zika virus, an emerging flavivirus, generally causes mild infection in adult humans but is associated with severe neurologic complications and adverse fetal outcomes.  Zika virus is transmitted to humans primarily by Aedes mosquitoes. However, male to female sexual transmission seems possible and infectious virus was detected in semen from a patient with haematospermia during the 2013–14 French Polynesia outbreak.  Now, a study from researchers led by Inserm confirms that the Zika virus can be transmitted sexually. The team state that their findings have shown 100% genetic correlation between the form of the virus present in a man who contracted the virus in Brazil and that of a woman who had never travelled in the epidemic area, and who had sexual relations with him. The opensource study is published in The New England Journal of medicine.

Previous studies have shown that although Zika infection usually causes mild symptoms, it can be responsible for severe neurological complications, particularly in the infant of a woman infected while pregnant. The Zika virus, a member of the Flavivirus family, is almost exclusively transmitted to humans by Aedes mosquitoes, however, some indications of possible sexual transmission of the virus have been reported before now.  Two studies have shown the presence of infectious Zika virus in semen. A recent article described detection of Zika virus RNA in semen 62 days after the onset of illness, however, the infectious virus was not cultured.  The current study, has for the first time, been able to culture the infecting virus from two people seeking a consultation for suspected Zika virus infection.

The current study analysed specimens of urine, saliva and blood taken from a man who returned from Brazil, and contracted the virus there. The same specimens were taken from a sick woman who had sexual relations with this man, who had never travelled to an epidemic area.  Results show that while the virus was detected in the urine and saliva of the woman, analysis of the specimens showed that it was absent from the blood and saliva of the man, making it unlikely that transmission occurred via these routes.

The lab then tested the male patient’s semen for the virus, and detected high viral loads at 15 days and at 3 weeks after the patient’s return from Brazil.  The virus from both persons was individually sequenced, using a saliva sample from the female patient and a semen sample from the male patient, for genetic analysis. Results show 100% correlation between the two genetic sequences. The group state that apart from 4 mutations, all of them synonymous, the nucleotide sequences both encoded an identical form of the virus.

The team surmise that their molecular analyses confirms sexual transmission of Zika virus exists, and should be taken into consideration when making recommendations, due to its persistence in the semen several weeks after infection. For the future, the researchers state that the period for which men should have protected sexual relations, including oral sex, needs to be defined.

Source: INSERM (Institut national de la santé et de la recherche médicale)