MS06 - MEPI-2
Cartoon Room 2 (#3147) in The Ohio Union

Disease Dynamics Across Scales

Thursday, July 20 at 10:30am

SMB2023 SMB2023 Follow Thursday during the "MS06" time block.
Room assignment: Cartoon Room 2 (#3147) in The Ohio Union.
Note: this minisymposia has multiple sessions. The other session is MS07-MEPI-2 (click here).

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Joshua Caleb Macdonald, Hayriye Gulbudak


Infectious disease dynamics operate across biological scales: pathogens replicate within hosts, but transmit among populations. Functional changes in the pathogen-host interaction thus generate cascading effects across organizational scales. Management strategies and the degree to which these strategies are successfully implemented may create selection pressures which drive evolution and which in turn impact the efficacy of management strategies. Thus in both ecology and epidemiology improved mechanistic understanding of cross-scale effects represents a challenge of critical importance. Growing human populations and ecosystem destruction is bringing humans into closer contact with other animals. As such epidemics and pandemics are expected to increase in frequency in the coming decades. Thus increased understanding of methods to control the spread of disease at the population level and of the mechanisms by which diseases replicate and interact with the immune system at the within-host level are of critical importance.In this mini-symposium we present talks that seek to understand disease dynamics within and across differing organizational scales.

Anna Jolles

Oregon State University (Carlson College of Veterinary Medicine and Department of Integrative Biology)
"Mechanisms of persistence of highly transmissible foot-and-mouth viruses in their maintenance host, African buffalo (Syncerus caffer)"
Extremely contagious pathogens are a global biosecurity threat because of their high burden of morbidity and mortality, as well as their capacity for fast-moving epidemics that are difficult to quell. Understanding the mechanisms enabling persistence of highly transmissible pathogens in host populations is thus a central problem in disease ecology. Through a combination of experimental and theoretical approaches, we investigated how highly contagious foot-and-mouth disease viruses persist in the African buffalo, which serves as their wildlife reservoir. We found that viral persistence through transmission among acutely infected hosts alone is unlikely. Working with three viral strains (SAT1,2,3), we found that different strains appear to utilize distinct mechanisms to ensure their long-term persistence in their maintenance host: The inclusion of occasional transmission from persistently infected carriers reliably rescues the most infectious viral strain (SAT1) from fade-out. We observed that antibody titers against FMD viruses are surprisingly dynamic in buffalo; and show that frequent drops in antibody protection can allow persistence of the least transmissible strain we studied (SAT3). The persistence of SAT2 remains somewhat enigmatic - additional mechanisms such as antigenic shift, or spillover among host populations may be required for its persistence.
Additional authors: Ricardo Noe Gerardo Reyes Grimaldo, Brianna Beechler, Bryan Charleston, Lin-Marie de Klerk-Lorist, Erin Gorsich, Simon Gubbins, Francois Maree, Eva Perez-Martin, Katherine Scott, Louis van Schalkwyk, Fuquan Zang, Jan Medlock

Simon Gubbins

The Pirbright Institute (Transmission Biology)
"Cross-scale dynamics of foot-and-mouth disease virus: from within hosts to between farms"
Foot-and-mouth disease virus (FMDV) infects cloven-hoofed livestock and wildlife species. It causes foot-and-mouth disease (FMD), which has substantial economic impacts for endemic countries and for disease-free countries when epidemics occur in them. Because of its importance FMDV has been studied at a range of scales from within a host to continental scale. This provides an opportunity to develop data-driven multi-scale models for FMDV and to examine how process at one scale affect process at another. In this presentation we will discuss a mathematical and statistical framework for linking models for FMDV at different scales (within-host, between-host and between-farm) to investigate how the dynamics at one scale influences dynamics at another. For example, we can use the models to show how within-host parameters (e.g. viral growth and clearance rates) influence between-host transmission (reproduction numbers) and how within-farm transmission (e.g. via direct contact or a contaminated environment) affects between-farm transmission. The models are parameterised using Bayesian methods applied to a combination of data from transmission experiments, within-farm outbreaks and regional epidemics. This allows us to test model assumptions and to incorporate parameter uncertainty at one scale in predictions at another.
Additional authors: John Ellis, The Pirbright Institute

Jan Medlock

Oregon State University (Biomedical Sciences)
"The Persistence of Foot-and-Mouth Disease Virus in African Buffalo"
Foot-and-mouth disease virus (FMDV) is a very important trade-restricting livestock disease. In sub-Saharan Africa, buffalo act as reservoir for FMDV, challenging global eradication and local economies. However, little is known about the dynamics of FMDV in African buffalo. We conducted FMDV infection experiments to quantify epidemiologic parameters of FMDV transmission in buffalo, and a 3-year cohort study to document birth timing, and duration of maternal protection from FMDV infection. We used Bayesian inference to estimate parameters, and constructed a rigorous quantitative framework that explicitly incorporates individual variation in birth rates, waning of maternal antibodies, and epidemiological parameters into predictions about disease persistence from an individual-based stochastic model. We used our model to show that FMDV's high transmission rate, short infectious period, and long-term immunity, when combined with the buffalo’s seasonal variation in births, fails to explain the persistence of FMDV from year to year. We showed that an alternative hypothesis, based on infection experiments, that FMDV forms some long-term carriers after acute infection does explain the persistence for one of the three circulating serotypes in southern Africa. I will also discuss work-in-progress on hypotheses that may explain the persistence of the two remaining serotypes.
Additional authors: Ricardo Noe Gerardo Reyes Grimaldo, Oregon State University; Anna Jolles, Oregon State University; Erin Gorsich, University of Warwick; Simon Gubbins, The Pirbright Institute; Brianna Beechler, Oregon State University; Peter Buss, SANParks; Nick Juleff, Bill & Melinda Gates Foundation; Lin-Mari de Klerk-Lorist, Office of the State Veterinarian, Department of Agriculture, Land Reform and Rural Development, Government of South Africa; Francois Maree, Onderstepoort Veterinary Institute; Eva Perez-Martin, The Pirbright Institute; O.L. van Schalkwyk, Office of the State Veterinarian, Department of Agriculture, Land Reform and Rural Development, Government of South Africa; Katherine Scott, Onderstepoort Veterinary Institute; Fuquan Zhang, Institute of Prion Diseases, University College London; Bryan Charleston, The Pirbright Institute

Cameron Browne

University of Louisiana at Lafayette (Mathematics)
"Environmental adaptation and seasonality in cholera eco-evolutionary dynamics"
Cholera epidemics are largely driven by direct transmission from person to person or indirectly through environment, although Vibrio cholerae is also capable of growth and long-term survival in aquatic ecosystems. In this talk, I will discuss recent mathematical modeling work showing how fluctuations and strain evolution in the environment impacted the cholera outbreak in Haiti beginning in 2010. First, we calibrate a stochastic multi-strain mixed-transmission dynamic model of V. cholerae to phylogenetic, case and seasonal rainfall data from Haiti. Along with fitting the clinical incidence, we connect genetic diversity and a coalescence process in model simulations to the effective population size computed from serially sampled cholera genomes. The results suggest that environmental replication actively contributes to genetic diversification and environmental adaptation, which can impact the success of different control measures. Mathematical analysis of the underlying deterministic model is challenging, however competitive exclusion is proved in the absence of environmental replication and seasonality. Assuming only partial cross-immunity in this case does induce coexistence of two strains (called serotypes) and serotype cycling with seasonal forcing, which may explain switching of serotype dominance observed in Haiti.
Additional authors: Leah LeJeune, University of Louisiana at Lafayette; Carla Mavian, University of Florida

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