Modelling Mosquito-Borne And Sexual Transmission Of Zika Virus In Australia: Risks To Blood Transfusion Safety

Background: Since 2015, Zika virus (ZIKV) outbreaks have occurred in the Americas and the Pacific involving mosquito-borne and sexual transmission. ZIKV has also emerged as a risk to global blood transfusion safety. Aedes aegypti, a mosquito well established in north and some parts of central and southern Queensland, Australia, transmits ZIKV. Aedes albopictus, another potential ZIKV vector, is a threat to mainland Australia. Australia has not yet reported local transmission of ZIKV. However, due to the close proximity to, and frequent air traffic with many neighboring countries endemic for ZIKV, a history of imported cases acquired overseas, the current favourable conditions for local transmission and, a potential high rate of asymptomatic infection, transmission is plausible, and could pose a risk to public health. Since these conditions create the potential for local transmission in Australia and a possible uncertainty in the effectiveness of blood donor risk-mitigation programs, we investigated the impact of mosquito-borne and sexual transmission of ZIKV in Australia on local blood transfusion safety. Methods and materials: We modelled ‘best-’ and ‘worst-’ case scenarios of monthly reproduction number (R0) for both transmission pathways of ZIKV from 1996–2015 in 11 localities, by varying epidemiological and entomological estimates. We then estimated the attack rate and subsequent number of infectious people to quantify the ZIKV transfusion-transmission risk using the European Up-Front Risk Assessment Tool. Results: Epidemic potential existed for ZIKV transmission in Cairns, Rockhampton, Thursday Island, Townsville, and theoretically in Brisbane and Darwin during the warmest months of the year. The yearly estimation of the risk of transmitting ZIKV infection by blood transfusion remained low through the study period for all locations, except for Cairns, Darwin, Rockhampton and Townsville, ranging from one in 390,000 to one in 57,100. Conclusion: Given the increasing demand for plasma products in Australia, the current strategy of restricting donors returning from infectious disease outbreak regions to source plasma collection provides a simple and effective risk management approach. However, if local transmission was suspected in the main urban centres of Australia, potentially facilitated by the geographic range expansion of Ae. aegypti or Ae. albopictus, this mitigation strategy would need urgent review.