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Advancing Molecular Epidemiology: Enhanced Methods and Applications in Pathogen Transmission Network AnalysisWeaver, Steven, 0000-0002-6931-7191 12 1900 (has links)
The use of genomic information has gained increasing relevance in epidemiology and public health, particularly the inference of genetic
networks of highly evolving pathogens like HIV. This approach offers
objective evidence that allows for tracking transmission dynamics, and
guiding intervention. However, the virus's high
genetic diversity, combined with variations in risk factors and
transmission rates among affected populations, leads to substantial
differences in epidemic dynamics across different epidemiological contexts.
Additionally, transmission networks inferred using a distance threshold
often create many spurious edges among closely related sequences, resulting
in abiological transmission cycles. Management of these networks as new
sequences are generated also fuel a desire to track cluster growth over
time. It is therefore advisable to develop molecular analysis tools that
better capture the unique landscape of each epidemic, providing a portrayal
that more closely mirrors the real epidemic scenario. This dissertation
introduces novel tools aimed at optimizing genetic network analysis for
epidemiological purposes, with a focus on HIV-1 but with stated potential
further application in other pathogens.
Due to their greater convenience compared to phylogenetic methods, the inference of transmission networks through genetic distance methods has been
widely used for near-real-time surveillance of HIV-1. Published research using
the HIV-TRACE software package frequently uses the default threshold of 0.015
substitutions/site for HIV \textit{pol} gene sequence. In Chapter 2, Weaver
\textit{et al.} introduces AUTO-TUNE, a heuristic scoring method to adaptively
tune the distance threshold, to prevent giant cluster formation and maximize
cluster numbers. This method was applied to various outbreaks, considering
regional or temporal differences, to identify clusters with specific risk
factors. For instance, we found the 0.015 threshold suits US-like epidemics,
but a lower threshold of 0.005 better captures outbreaks like the CRF07 BC
subtype among MSM in China. Conversely, a larger threshold is needed for
regions where diverse risk factors and sparse sampling occur over longer
periods. This adaptive approach aids public health officials in making more
informed interventions.
Genetic distance and phylogenetic tools often yield densely connected clusters, with many spurious edges that create unrealistic cycles, overestimating
connectivity and inflating node degrees. In Chapter 4, we present a scalable
approach, Conditionally Orthogonal Vertices For Edge Filtering in Epidemics
(COVFEFE), to prune spurious edges through a straightforward application of the
PC (unroll) algorithm originally developed for Bayesian graphical models.
COVFEFE removes edges likely to be indirect, preserving cluster membership. It
eliminates 29\%–80\% of spurious edges in simulated transmission chains with
low intra-host mutation rates and 4\%–39\% in real HIV-1 epidemic data, often
simplifying dense clusters to chains. Filtered networks align better with
theoretical models, affecting analysis and modeling methods that use node or
edge properties. COVFEFE is part of the HIV-TRACE molecular network inference
package.
The heterogeneity in risk factors and characteristics of the HIV-1 epidemic worldwide demands adapting bioinformatics tools for different contexts to meet
local needs. In Chapter 4, we present HIV-TRACE GO, an extension of the
HIV-TRACE software designed to enhance global HIV molecular epidemiology
surveillance. This web application, developed primarily in JavaScript, enables
real-time molecular surveillance with features tailored for
multi-jurisdictional data management and internationalization. HIV-TRACE GO has
been successfully implemented at CIENI-INER, a WHO-accredited HIV-1 sequencing
reference laboratory in Mexico, demonstrating its feasibility for both local
and international applications. We discuss the software architecture, key
customizations, and its potential impact on public health surveillance. / Biology
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