Research

Read about my recent research on Chagas vectors and their feeding habits, in UVM Today, and at The CDC.

My current research is on the evolution and ecology of host-pathogen interactions, especially population genetics of invertebrate hosts of Chagas' disease and whirling disease, computational biology including spatial models of evolution, mathematical biology.

Overall Research Objective: Understand the spatial pattern of variation in prevalence of infection by examining the ecological and evolutionary factors that govern the distribution and abundance of pathogens and their hosts.

Organisms are constantly and continuously exposed to harmful pathogens and evolution through natural selection has responded with a myriad of host-parasite interactions. When organisms are exposed to pathogens they might or might not become infected depending on these interactions.

My studies of infectious pathogens includes a rich assortment of topics, including host-pathogen population dynamics, host specificity, the evolution of virulence, and the costs of resistance and defense.These investigations  use molecular ecology, population genetics, and complex systems modeling.

Chagas Disease: Chagas disease, caused by Trypanosoma cruzi, afflicts up to 11 million people in Latin America and causes potentially life-threatening disease in up to one third of those infected. Reducing new infections of Chagas disease ultimately depends on vector control. Knowledge of vector population structure and sources of infesting insects are vital to the success of vector control strategies; however, the extent of population structure, migration between populations, and the source(s) of re-infestation following insecticide application are virtually unknown. We are working to develop a basic understanding of the molecular population genetics of the insect vectors in endemic areas in Bolivia and Guatemala. Our population genetic studied are helpful because vector control efforts require an understanding of migration. Understanding the dynamics of vector population structure will ultimately lead to more effective control of T. cruzi transmission.

The work is done in collaboration with Juan Carlos Pizarro, Universidad de San Francisco Xavier, Sucre, Bolivia, Patricia Dorn Loyola University, New Orleans and Carlota Monroy, Universidad de San Carlos de Guatemala. My graduate students David Lucero and Nick De La Rua are also working on Chagas disease.

Whirling Disease: In collaboration with Billie L. Kerans (Montana State University), and Donna M. Rizzo (University of Vermont), I am helping to characterize Oligocheate communities to monitor Myxobolus cerebralis infection on the Madison River, MT.

In the 1950's, the fish parasite, Myxobolus cerebralis invaded the US from Europe. The parasite invades cartilagenous skeletal tissue surrounding the brain causing fish to swim in circles, hence the name. Whirling disease has devastated populations of wild rainbow trout (Oncorhynchus mykiss) and is contributing to the decline of Yellowstone cutthroat trout (O. clarki bouvieri). Although M. cerebralis has been detected in watersheds throughout much of the US, the distribution and severity of whirling disease is both regionally and locally variable.

Myxobolus cerebralis has a two-host life cycle alternating between salmonid fish and the oligochaete worm, Tubifex tubifex. We are examining how the introduced parasite affects genetic variation in the invertebrate host, disease incidence in the vertebrate host and ultimately community dynamics.

Complex Systems Modeling: I work on two types of computational models genetic algorithms and artificial neural networks. My lab is developing evolutionary algorithms for the evolution of defenses. The work is done in collaboration with Dr. Donna M. Rizzo (College of Engineering and Mathematical Sciences, UVM). The project examines multi-objective optimization models for the evolution of costly vs cost-free defenses in the context of spatial and temporal variation in pathogen prevalence.

Information for Prospective Graduate Students: If you are interested in the evolution and ecology of host-parasite interactions from a population genetics perspective and want to do collaborative empirical or theoretical work to rigorously test hypotheses, please contact me via e-mail.

Selected Recent Publications:

Stevens, L., P. Dorn, J. Hobson, N. de la Rua, D. Lucero, J. Klotz, J. Schmidt and S. A. Klotz (2012). "Vector Blood Meals and Chagas Disease Transmission Potential, United States." Emergining Infectious Diseases 18: in press.

Lodh, N., B. L. Kerans and L. Stevens (2012). "The Parasite that Causes Whirling Disease, Myxobolus cerebralis, is Genetically Variable Within and Across Spatial Scales." The Journal of Eukaryotic Microbiology 59: 80-87.

Stevens, L., P. L. Dorn, J. Klotz, J. Schmidt, D. Lucero and S. A. Klotz (2011). "Kissing Bugs. The Vectors of Chagas." Advances in Parasitology 75: 169-192.

Klotz, S. A., L. Stevens, P. L. Dorn, J. O. Schmidt and J. H. Klotz (2011). The Kissing Bugs of the United States. Kansas School Naturalist. D. o. B. P. Emporia State University. Emporia, KS. 57.

de la Rua, N., L. Stevens and P. L. Dorn (2011). "High genetic diversity in a single population of Triatoma sanguisuga (LeConte, 1855) inferred from two mitochondrial markers: Cytochrome b and 16S ribosomal DNA." Infection Genetics and Evolution 11: 671-677.

Klotz, J., P. L. Dorn, J. L. Logan, L. Stevens, J. L. Pinnas, J. Schmidt and S. A. Klotz (2010). "Kissing Bugs: Potential disease vectors and cause of anaphylaxis." Clinical Infectious Diseases 50: 1629-1634.

Mouser, P. J., D. M. Rizzo, G. Druschel, S. E. Morales, N. Hayden, P. O’Grady and L. Stevens (2010). "Enhanced detection of groundwater contamination from a leaking waste disposal site by microbial community profiles." Water Resources Research 46: W12506.

Pizarro, J. C. and L. Stevens (2008). "A New Method for Forensic DNA Analysis of the Blood Meal in Chagas Disease Vectors Demonstrated Using Triatoma infestans from Chuquisaca, Bolivia." PLoS ONE 3(10).

Pizarro, J. C., L. M. Gilligan and L. Stevens (2008). "Microsatellites Reveal a High Population Structure in Triatoma infestans from Chuquisaca, Bolivia." PLoS Neglected Tropical Diseases 2(3).

Stevens, L. and D. M. Rizzo (2008). "Local adaptation to biocontrol agents: A multi-objective data driven optimization model for the evolution of resistance." Ecological Complexity 5(3): 252-259.

Pizarro, J. C., D. Lucero and L. Stevens (2007). "A method for the identification of guinea pig blood meal in the Chagas disease vector, Triatoma infestans." Kinetoplastid Biol Dis 6: 1.

Tucker, T. M. and L. Stevens (2003). "Geographical variation and sexual dimorphism of phenoloxidase levels in Japanese beetles (Popillia japonica)." Proceedings of the Royal Society of London Series B-Biological Sciences 270: S245-S247.

Rigby, M. C., R. F. Hechinger and L. Stevens (2002). "Why should parasite resistance be costly?" Trends Parasitol 18(3): 116-120.

Stevens, L., R. Giordano and R. F. Fialho (2001). "Male-killing, nematode infections, bacteriophage infection, and virulence of cytoplasmic bacteria in the genus Wolbachia." Annual Review of Ecology and Systematics 32: 519-545.

Fialho, R. F. and L. Stevens (2000). "Male-killing Wolbachia in a flour beetle." Proceedings of the Royal Society of London Series B-Biological Sciences 267(1451): 1469-1473.

Warning: include() [function.include]: Unable to access faculty_list.html in /fs/a6/users/b/i/biology/public_html/faculty/stevens.php on line 60

Warning: include(faculty_list.html) [function.include]: failed to open stream: Permission denied in /fs/a6/users/b/i/biology/public_html/faculty/stevens.php on line 60

Warning: include() [function.include]: Failed opening 'faculty_list.html' for inclusion (include_path='.:/usr/local/lib/php:/usr/local/lib/php/uvm/include:/usr/local/uvm-inc') in /fs/a6/users/b/i/biology/public_html/faculty/stevens.php on line 60