Understanding the survival of Zika virus in a vector interconnected sexual contact network

Authors: FERDOUSI, TANVIR - Kansas State University; Cohnstaedt, Lee; McVey, David; SCOGLIO, CATERINA - Kansas State University

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2019
Publication Date: 5/10/2019
Citation: Ferdousi, T., Cohnstaedt, L.W., McVey, D.S., Scoglio, C.M. 2019. Understanding the survival of Zika virus in a vector interconnected sexual contact network. Scientific Reports. 9:7253. https://doi.org/10.1038/s41598-019-43651-3.
DOI: https://doi.org/10.1038/s41598-019-43651-3

Interpretive Summary: In this study we have proposed an individual based interconnected network model for ZIKV that can also be used to simulate any vector-borne disease that features contact based direct transmissions. We employed heterogeneous mixing based on the host contact network which is generated based on real world data on human sexual behavior, sexual orientation, gender, and age structure. Initially, we explored how the seasons can affect this predominantly vector-borne disease. Later, we focused on the survival of pathogen in the climates similar to Florida if an outbreak starts prior to the colder months. Finally, we utilized a sensitivity analysis to evaluate our model behavior in response to changes in some key parameters. Our seasonal analysis results indicated that outbreak size is strongly related to the environmental conditions during season of the pathogen introduction. The first few weeks are crucial in determining to what extent the vector-borne pathogen would spread. After that period, environmental variations have a much weaker effect in reducing or increasing the outbreak size. If the pathogen is introduced during the peak mosquito season, there is a high probability that larger outbreaks will occur. Even if climatic suitability of mosquito vectors declines rapidly after the first few weeks, the vectors still manage to spread the pathogen in the host population rapidly and may cause substantial outbreaks. This suggests that a ZIKV outbreak may spread rapidly out of control if it is not effectively contained during the initial stage. Therefore, early interventions are crucial. This may be complicated by the fact that it may be difficult to rapidly identify outbreaks due to the large asymptomatic group of infected hosts. The ratio of vector to host, as expected, has is a dominating factor that determines the total outbreak incidence and the length. We also determined that sexual transmission is a relatively small component to the overall incidence of infection, which is dominated by vectored-transmission. However, this viral pathogen still survives up to 75 days in the host network without further transmission by infected, competent vectors. This long survival can be attributed to a small amount of sexual transmission but it is mainly due to the extended infectiousness (convalescence) of the hosts as it is assumed that pathogen can survive up to a month in the semen of recovering males. The use of birth control methods (e.g. condoms) could be effective in reducing the spread of pathogen during this recovery period. Further clinical studies are warranted in this area to test the efficacy of suggested control measures.

Technical Abstract: The recent outbreaks of the insect-vectored Zika virus have demonstrated its potential to be sexually transmitted, which complicates modeling and our understanding of disease dynamics. Autochthonous outbreaks in the US mainland may be a consequence of both modes of transmission, which affect the outbreak size, duration, and virus persistence. We propose a novel individual-based interconnected network model that incorporates both insect-vectored and sexual transmission of this pathogen. This model interconnects a homogeneous mosquito vector population with a heterogeneous human host contact network. The model incorporates the seasonal variation of mosquito abundance and characterizes host dynamics based on age group and gender in order to produce realistic projections. We use a sexual contact network which is generated on the basis of real world sexual behavior data. Our findings suggest that for a high relative transmissibility of asymptomatic hosts, Zika virus shows a high probability of sustaining in the human population for up to 3 months without the presence of mosquito vectors. Zika outbreaks are strongly affected by the large proportion of asymptomatic individuals and their relative transmissibility. The outbreak size is also affected by the time of the year when the pathogen is introduced. Although sexual transmission has a relatively low contribution in determining the epidemic size, it plays a role in sustaining the epidemic and creating potential endemic scenarios.