Vaccination simulation: using epidemiological network models to inform pathogen control strategies for wildlife conservation

Many endangered wildlife populations are vulnerable to infectious diseases for which vaccines exist; yet, endangered species are rarely vaccinated, in part owing to the challenges in immunizing large portions of a population.... [ view full abstract ]

Many endangered wildlife populations are vulnerable to infectious diseases for which vaccines exist; yet, endangered species are rarely vaccinated, in part owing to the challenges in immunizing large portions of a population. Traditional disease modeling approaches assume individual contact rates are constant within a population; however, this is not the case for many wildlife species, where individuals vary in frequency and duration of contact with conspecifics. Social interactions can be formalized as contact networks, which have great potential to better interpret the spread of infectious disease within susceptible wildlife populations. Focusing intervention efforts on individuals with the highest contact rates could minimize the number of animals requiring vaccination. Great apes demonstrate tremendous variation in social contacts and have experienced major population declines from directly-transmitted pathogens. We present here a study using detailed behavioral association data and epidemiological network models to design and evaluate disease intervention strategies for a wild primate population. Outbreaks were simulated on monthly contact networks parameterized with association data from a wild chimpanzee community to ask how final outbreak size depends on pathogen infectiousness, outbreak timing, and network position of the index case. By determining traits associated with individuals most likely to spark large epidemics, we identified “risk groups” that could be targeted for pathogen control. Simulations of three vaccination strategies revealed that compared to random vaccinations, the number of animals requiring immunization to curb outbreaks could be reduced by up to 35% if chimpanzees were vaccinated based on greatest network centrality and by up to 18% if efforts focused on individuals from easily identifiable risk groups. Overall, our work demonstrates the use and versatility of epidemiological network models for informing wildlife vaccination strategies.