Virulence and Vertical Transmission of Two Genotypically and Geographically Diverse Isolates of Trypanosoma cruzi in Mice

Hall, Christopher; Pierce, Emily M.; Wimsatt, Ashley N.; Hobby-Dolbeer, Traci; Meers, J. Brad

doi:10.1645/ge-2296.1

Cited by 15 publications

(17 citation statements)

References 32 publications

(31 reference statements)

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“…However, if we suppose that rats are more like the lab mice in [18] than like raccoons, strain 2 can win in the woodrat cycle as well. For the given values, if we assume that p 2W ≥ 0.25 (hence p w max ≥ 0.375 as in Table 2), then strain 2 wins if adapted to oral transmission, and for higher values of p 2W (e.g.…”

Section: Trade-off and Competitionmentioning

confidence: 99%

The role of adaptations in two-strain competition for sylvaticTrypanosoma cruzitransmission

Kribs-Zaleta¹,

Mubayi²

2012

Journal of Biological Dynamics

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This study presents a continuous-time model for the sylvatic transmission dynamics of two strains of Trypanosoma cruzi enzootic in North America, in order to study the role that adaptations of each strain to distinct modes of transmission (classical stercorarian transmission on the one hand, and vertical and oral transmission on the other) may play in the competition between the two strains. A deterministic model incorporating contact process saturation predicts competitive exclusion, and reproductive numbers for the infection provide a framework for evaluating the competition in terms of adaptive trade-off between distinct transmission modes. Results highlight the importance of oral transmission in mediating the competition between horizontal (stercorarian) and vertical transmission; its presence as a competing contact process advantages vertical transmission even without adaptation to oral transmission, but such adaptation appears necessary to explain the persistence of (vertically-adapted) T. cruzi IV in raccoons and woodrats in the southeastern United States.

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Section: Trade-off and Competitionmentioning

confidence: 99%

The role of adaptations in two-strain competition for sylvaticTrypanosoma cruzitransmission

Kribs-Zaleta¹,

Mubayi²

2012

Journal of Biological Dynamics

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“…If we use the data on the probability of vertical transmission in mice of [23], i.e., p 1 = 1/3 and p 2 = 2/3, and the estimates of the probability of oral transmission of [10], and assume that T. cruzi I and IIa are equally transmitted via this pathway, i.e., ρ 1 = ρ 2 = 0.177 host/vector, the condition A < β h1 < B for Q to affect the outcome of the competition between the two strains (see section 3.1) becomes: 2 β h2 + 0.177 H < β h1 < 2 β h2 + 0.177 H Q v /Q h when Q h < Q v and 2 β h2 + 0.177 H Q v /Q h < β h1 < 2 β h2 + 0.177 H when Q h < Q v . Even if no precise data is available for the maximum rate at which hosts consume vectors in the field, H, the consumption of one vector per host and per year has been shown numerically to be sufficient to account for the observed T.cruzi prevalences in the SE US [13].…”

Section: Fit With Available Datamentioning

confidence: 99%

“…Vertical transmission has been reported among placental hosts such as rats and mice [22,23], and humans [24]. In addition, sylvatic hosts such as raccoons and opossums are opportunistic feeders whose diet includes insects, and experimental studies have shown that they can get infected by ingesting infected vectors [25,26].…”

Section: Introductionmentioning

confidence: 99%

“…It is therefore most likely that type I overcomes type II at stercorarian transmission efficiency. In regard to vertical transmission, an experiment showed that mice infected experimentally with T. cruzi IIa transmit the parasite to 66 percent of their offspring, compared to 33 percent for T. cruzi I, although type IIa parasitemias are drastically smaller than type I ones [23]. T. cruzi IIa seems therefore better adapted to vertical transmission, possibly via a better ability to invade reproductive tissues compared to T. cruzi I [23,30].…”

Section: Introductionmentioning

confidence: 99%

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The role of the ratio of vector and host densities in the evolution of transmission modes in vector-borne diseases. The example of sylvatic Trypanosoma cruzi

Pelosse

Kribs-Zaleta

2012

Journal of Theoretical Biology

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Pathogens may use different routes of transmission to maximize their spread among host populations. Theoretical and empirical work conducted on directly-transmitted diseases suggest that horizontal (i.e., through host contacts) and vertical (i.e., from mother to offspring) transmission modes trade off, on the ground that highly virulent pathogens, which produce larger parasite loads, are more efficiently transmitted horizontally, and that less virulent pathogens, which impair host fitness less significantly, are better transmitted vertically. Other factors than virulence such as host density could also select for different transmission modes, but they have barely been studied. In vector-borne diseases, pathogen transmission rate is strongly affected by host-vector relative densities and by processes of saturation in contacts between hosts and vectors. The parasite Trypanosoma cruzi which is transmitted by triatomine bugs to several vertebrate hosts is responsible for Chagas' disease in Latin America. It is also widespread in sylvatic cycles in the southeastern U.S. in which it typically induces no mortality costs to its customary hosts. Besides classical transmission via vector bites, alternative ways to generate infections in hosts such as vertical and oral transmission (via the consumption of vectors by hosts) have been reported in these cycles. The two major T. cruzi strains occurring in the U.S. seem to exhibit differential efficiencies at vertical and classical horizontal transmissions. We investigated whether the vector-host ratio affects the outcome of the competition between the two parasite strains using an epidemiological two-strain model considering all possible transmission routes for sylvatic T. cruzi. We were able to show that the vector-host ratio influences the evolution of transmission modes providing that oral transmission is included in the model as a possible transmission mode, that oral and classical transmissions saturate at different vector-host ratios and that the vector-host ratio is between the two saturation thresholds. Even if data on parasite strategies and demography of hosts and vectors in the field are crucially lacking to test to what extent the conditions needed for the vector-host ratio to influence evolution of transmission modes are plausible, our results open new perspectives for understanding the specialization of the two major T. cruzi strains occurring in the U.S. Our work also provides an original theoretical framework to investigate the evolution of alternative transmission modes in vector-borne diseases.

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“…In Texas and northern Mexico, meanwhile, both strains are found at roughly equal levels in woodrats (Neotoma micropus) [4]. T. cruzi I is often described as chagasic and more virulent (see, e.g., [19]) compared to T. cruzi IV, which has been found to be better adapted to vertical transmission [11], and the importance of vertical and oral transmission in an epidemiological landscape where classical stercorarian transmission is disadvantaged almost surely plays a role in mediating interstrain competition here. Host-vector interactions-in particular, the two distinct contact processes that cause stercorarian and oral infection of hosts-add an extra layer to the epidemiological landscape, extending the framework of Levins to incorporate the densities of not only the parasite but also the hosts and vectors.…”

Section: Introductionmentioning

confidence: 99%

Graphical analysis of evolutionary trade-off in sylvatic Trypanosoma cruzi transmission modes

Kribs-Zaleta

2014

Journal of Theoretical Biology

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Evolutionary trade-off (one attribute increasing at the expense of another) is a central notion in 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 hostsstercorarian, vertical, and oral-in response to an epidemiological landscape that involves both hosts and vectors. Using a fitness measure derived from an invasion reproductive number, this study analyzes several different trade-off scenarios in cycles involving raccoons or woodrats, and finds 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 trade-off.

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Virulence and Vertical Transmission of Two Genotypically and Geographically Diverse Isolates of Trypanosoma cruzi in Mice

Cited by 15 publications

References 32 publications

The role of adaptations in two-strain competition for sylvaticTrypanosoma cruzitransmission

The role of adaptations in two-strain competition for sylvaticTrypanosoma cruzitransmission

The role of the ratio of vector and host densities in the evolution of transmission modes in vector-borne diseases. The example of sylvatic Trypanosoma cruzi

Graphical analysis of evolutionary trade-off in sylvatic Trypanosoma cruzi transmission modes

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