Christopher Kribs, Ph.D.
http://hdl.handle.net/10106/24305
2024-03-29T13:25:37ZGraphical analysis of evolutionary trade-off in sylvatic Trypanosoma cruzi transmission modes
http://hdl.handle.net/10106/26060
Graphical analysis of evolutionary trade-off in sylvatic Trypanosoma cruzi transmission modes
Kribs, Christopher
**Please note that the full text is embargoed** ABSTRACT: The notion of evolutionary trade-off (one attribute increasing at the expense of another) is central to the evolution of traits, well-studied especially in life-history theory, where a framework first developed by Levins illustrates how internal (genetics) and external (fitness landscapes) forces interact to shape an organism׳s ongoing adaptation. This manuscript extends this framework to the context of vector-borne pathogens, with the example of Trypanosoma cruzi (the etiological agent of Chagas׳ disease) adapting via trade-off among three different infection routes to hosts—stercorarian, vertical, and oral—in response to an epidemiological landscape that involves both hosts and vectors (where, in particular, parasite evolution depends not on parasite density but on relative host and vector densities). Using a fitness measure derived from an invasion reproductive number, this study analyzes several different trade-off scenarios in cycles involving raccoons or woodrats, including a proper three-way trade-off (two independent parameters). Results indicate that selection favors oral transmission to raccoons but classical stercorarian transmission to woodrats even under the same predation rate, with vertical (congenital) transmission favored only when aligned with dominant oral transmission or (at trace levels) under a weak (convex) trade-off.
Author's final draft after peer review, also known as a post print.
2014-07-01T00:00:00ZAgent-based mathematical modeling as a tool for estimating T. cruzi vector-host contact rates
http://hdl.handle.net/10106/26059
Agent-based mathematical modeling as a tool for estimating T. cruzi vector-host contact rates
Kribs, Christopher; Young, Kamuela E.; Mubayi, Anuj
**Please note that the full text is embargoed** ABSTRACT: The parasite Trypanosoma cruzi, spread by triatomine vectors, affects over 100 mammalian
species throughout the Americas, including humans, in whom it causes Chagas’ disease. In the
U.S., only a few autochthonous cases have been documented in humans, but prevalence is high
in sylvatic hosts (primarily raccoons in the southeast and woodrats in Texas). The sylvatic
transmission of T. cruzi is spread by the vector species Triatoma sanguisuga and Triatoma
gerstaeckeri biting their preferred hosts and thus creating multiple interacting vector-host cycles.
The goal of this study is to quantify the rate of contacts between different host and vector species
native to Texas using an agent-based model framework. The contact rates, which represent bites,
are required to estimate transmission coefficients, which can be applied to models of infection
dynamics. In addition to quantitative estimates, results confirm host irritability (in conjunction
with host density) and vector starvation thresholds and dispersal as determining factors for
vector density as well as host-vector contact rates.
Author's final draft after peer review, also known as a post print.
2015-11-01T00:00:00ZHost switching vs. host sharing in overlapping sylvatic Trypanosoma cruzi transmission cycles
http://hdl.handle.net/10106/26058
Host switching vs. host sharing in overlapping sylvatic Trypanosoma cruzi transmission cycles
Kribs, Christopher David; Mitchell, Christopher
The principle of competitive exclusion is well established for multiple populations competing for the same resource, and simple models for multistrain infection exhibit it as well when cross-immunity precludes coinfections. However, multiple hosts provide niches for different pathogens to occupy simultaneously. This is the case for the vector-borne parasite Trypanosoma cruzi in overlapping sylvatic transmission cycles in the Americas, where it is enzootic. This study uses cycles in the USA involving two different hosts but the same vector species as a context for the study of the mechanisms behind the communication between the two cycles. Vectors dispersing in search of new hosts may be considered to move between the two cycles (host switching) or, more simply, to divide their time between the two host types (host sharing). Analysis considers host switching as an intermediate case between isolated cycles and intermingled cycles (host sharing) in order to examine the role played by the host-switching rate in permitting coexistence of multiple strains in a single-host population. Results show that although the population dynamics (demographic equilibria) in host-switching models align well with those in the limiting models (host sharing or isolated cycles), infection dynamics differ significantly, in ways that sometimes illuminate the underlying epidemiology (such as differing host susceptibilities to infection) and sometimes reveal model limitations (such as host switching dominating the infection dynamics). Numerical work suggests that the model explains the trace presence of TcI in raccoons but not the more significant co-persistence observed in woodrats.
2015-09-01T00:00:00ZA metapopulation model for sylvatic T. cruzi transmission with vector migration
http://hdl.handle.net/10106/25815
A metapopulation model for sylvatic T. cruzi transmission with vector migration
Kribs, Christopher; Crawford, Britnee
This study presents a metapopulation model for the sylvatic transmission
of Trypanosoma cruzi, the etiological agent of Chagas' disease, across
multiple geographical regions and multiple overlapping host-vector transmission
cycles. Classical qualitative analysis of the model and several submodels
focuses on the parasite's basic reproductive number, illustrating how vector
migration across patches and multiple transmission routes to hosts (including
vertical transmission) determine the infection's persistence in each cycle. Numerical
results focus on trends in endemic [equilibrium] persistence levels as
functions of vector migration rates, and highlight the significance of the different
epidemiological characteristics of transmission in each of the three regions.
Author's final draft, known as pre-print.
2014-06-01T00:00:00Z