Zika virus transmission is associated to a mosquito bite (from an Aedes genus mosquito) and was isolated in 1948 from a macerate of mosquitoes of the Aedes africanus species collected at the Zika forest. Seroepidemiological studies based on blood samples obtained from residents in that region of Uganda have shown an anti-ZIKV antibody prevalence of around 6%. In addition, this virus has been repeatedly isolated from mosquitoes collected both in Africa and in Asia, leading to conclude that species such as Aedes africanus, Aedes aegypti and Aedes hensilli have a role in Zika virus enzootic maintenance (within a sylvatic environment).
The Ae. aegypti and Ae. albopictus competence for the transmission of Zika virus imposes a great public health concern. These arthropods are widely spread in tropical, sub-tropical (Ae. aegypti) and temperate (Ae. albopictus) areas, affecting a large number of susceptible people.
Sexual, perinatal and blood transfusion-transmitted Zika virus infection has been described, although less frequently and the magnitude of the epidemiological significance of these mechanisms has not yet been established.
In early 2016, a number of male-to-female sexual transmission cases of Zika virus infection were documented in the US. The women who sexually contracted the disease had no history of travel to affected areas. However, their male partners had traveled to countries where the virus is present. The onset of symptoms in these women was within 2 weeks of those experienced by their male partners. These cases highlight not only a mode of transmission other than through a mosquito vector, but also a possible post-infection carriage state in human semen. Prior to documentation of the transmission of Zika through sexual intercourse in the US, scientists in Tahiti confirmed the presence of the virus in the semen of a man 2 weeks or more after he recovered from a second bout of the disease.
The risk of the Zika virus being transmitted through transfusion of blood or blood products has also been a serious concern. In an attempt to address this issue, the World Health Organization (WHO) issued guidance on blood transfusions in Zika areas on 19 February 2016.
However, it is widely recognized that it is impossible in many Zika areas to halt blood transfusions, as recommended, and import blood from non-infected areas. WHO also recommended that red blood cells in affected areas be quarantined for seven to 14 days. If, after this period, the donor does not show any of the symptoms and signs of Zika infection, the red blood cells could be released. Unfortunately, there is currently no blood test for Zika infection other than the Zika RNA analysis, which is not routine.
1, Pinto Júnior VL, et al. Zika virus: a review to clinicians, Acta Med Port 2015 Nov-Dec;28(6):760-765
2, Pascal James Imperato, et al.The Convergence of a Virus, Mosquitoes, and Human Travel in Globalizing the Zika Epidemic, J Community Health DOI 10.1007/s10900-016-0177-7