title: Temperature and population density determine reservoir regions of seasonal persistence in highland malaria.
abstract: A better understanding of malaria persistence in highly seasonal environments such as highlands and desert fringes requires identifying the factors behind the spatial reservoir of the pathogen in the low season. In these 'unstable' malaria regions, such reservoirs play a critical role by allowing persistence during the low transmission season and therefore, between seasonal outbreaks. In the highlands of East Africa, the most populated epidemic regions in Africa, temperature is expected to be intimately connected to where in space the disease is able to persist because of pronounced altitudinal gradients. Here, we explore other environmental and demographic factors that may contribute to malaria's highland reservoir. We use an extensive spatio-temporal dataset of confirmed monthly Plasmodium falciparum cases from 1995 to 2005 that finely resolves space in an Ethiopian highland. With a Bayesian approach for parameter estimation and a generalized linear mixed model that includes a spatially structured random effect, we demonstrate that population density is important to disease persistence during the low transmission season. This population effect is not accounted for in typical models for the transmission dynamics of the disease, but is consistent in part with a more complex functional form of the force of infection proposed by theory for vector-borne infections, only during the low season as we discuss. As malaria risk usually decreases in more urban environments with increased human densities, the opposite counterintuitive finding identifies novel control targets during the low transmission season in African highlands.
authors.affiliation: Department of Geography and the Environment, University of Denver, 235 Boettcher West, 2050 East Iliff Avenue, Denver, CO 80208-0710, USA Frederick S. Pardee Center for International Futures, Josef Korbel School of International Studies, University of Denver, 2201 South Gaylord Street, Denver, CO 80208-0500, USA amirssha@gmail.com.
authors.forename: Amir S
authors.initials: AS
authors.lastname: Siraj
authors.affiliation: London School of Hygiene and Tropical Medicine, University of London, London WC1 E7HT, UK Catalan Institute of Climate Sciences (IC3), University of Barcelona, Doctor Trueta, 203 3a planta 08005 Barcelona, Spain.
authors.forename: Menno J
authors.initials: MJ
authors.lastname: Bouma
authors.affiliation: Department of Ecology and Evolution, University of Chicago, 1101 East 57th Street, Chicago, IL 60637, USA.
authors.forename: Mauricio
authors.initials: M
authors.lastname: Santos-Vega
authors.affiliation: PATH/ Malaria Control and Elimination Partnership in Africa, Africa Avenue, Getu Commercial Center, PO Box 493, Addis Ababa 1110, Ethiopia.
authors.forename: Asnakew K
authors.initials: AK
authors.lastname: Yeshiwondim
authors.affiliation: Frederick S. Pardee Center for International Futures, Josef Korbel School of International Studies, University of Denver, 2201 South Gaylord Street, Denver, CO 80208-0500, USA.
authors.forename: Dale S
authors.initials: DS
authors.lastname: Rothman
authors.affiliation: Oromia Regional Health Bureau, PO Box 24341, Addis Ababa, Ethiopia.
authors.forename: Damtew
authors.initials: D
authors.lastname: Yadeta
authors.affiliation: Department of Geography and the Environment, University of Denver, 235 Boettcher West, 2050 East Iliff Avenue, Denver, CO 80208-0710, USA School of Natural and Built Environments, University of South Australia, P Building, Mawson Lakes Campus, Mawson Lakes, South Australia 5095, Australia.
authors.forename: Paul C
authors.initials: PC
authors.lastname: Sutton
authors.affiliation: Department of Ecology and Evolution, University of Chicago, 1101 East 57th Street, Chicago, IL 60637, USA Howard Hughes Medical Institute, Chevy Chase, MD 20815-6789, USA.
authors.forename: Mercedes
authors.initials: M
authors.lastname: Pascual
mesh_terms: D000531:Altitude; D004196:Disease Outbreaks; D004197:Disease Reservoirs; D005002:Ethiopia / Q000453:epidemiology; D006801:Humans; D016778:Malaria, Falciparum / Q000453:epidemiology* / Q000635:transmission*; D010963:Plasmodium falciparum; D011156:Population Density; D011891:Rain; D012621:Seasons; D062211:Spatio-Temporal Analysis; D013696:Temperature
keywords: malaria; persistence; reservoir