June, 2004 Journal of Vector Ecology 177 Community ecology of small mammal populations in Panamá following an outbreak of Hantavirus pulmonary syndrome Luis A. Ruedas 1 , Jorge Salazar–Bravo 2 , David S. Tinnin 3 , Blas Armién 4 , Lorenzo Cáceres 4 , Arsenio García 4 , Mario Ávila Díaz 5 , Fernando Gracia 4 , Gerardo Suzán 6 , C. J. Peters 7 , Terry L. Yates 6 , and James N. Mills 8 1 Department of Biology and Museum of Vertebrate Biology, Portland State University, Science Building II, Room 232, Portland, OR 97207–0751, U.S.A. 2 Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409–3131, U.S.A. 3 Manter Laboratory of Parasitology, University of Nebraska, Lincoln, NE 68588–0514, U.S.A. 4 Instituto Conmemorativo Gorgas de Estudios de la Salud, Avenida Justo Arosemena, Panamá City, Panamá 5 Ministerio de Salud, Sección de Control de Vectores y Zoonosis, Región de Salud de Herrera, Edificio Carola, Chitré, Herrera, Panamá 6 Department of Biology and Museum of Southwestern Biology, University of New Mexico, Albuquerque, NM 87131–1091, U.S.A. 7 Department of Microbiology, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555–0609, U.S.A. 8 Special Pathogens Branch, Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Mail Stop A–26, 1600 Clifton Road, Atlanta, GA 30333, U.S.A. Received 7 August 2003; Accepted 13 December 2003 ABSTRACT: In late 1999 and early 2000, an outbreak of hantavirus pulmonary syndrome (HPS) occurred in and around Los Santos, on the Azuero Peninsula of southwestern Panamá. This HPS episode, resulting in 22% case fatality, was linked to the Costa Rican pigmy rice rat, Oligoryzomys fulvescens costaricensis, which harbored a then undescribed hantavirus, Choclo virus. In addition, Cherrie’s cane rat, Zygodontomys brevicauda cherriei, was identified as carrying a distinct hantavirus, Calabazo virus with no known pathogenicity to humans. Herein we present the ecological results of the outbreak investigations in the Azuero region. A total of 164 animals were captured, of which 126 were potential small, non–volant mammal hosts of a hantavirus: rodents in the family Muridae. There were significant differences in small mammal community structure between case sites and a negative control site. Differences were manifest in ecological measures of species diversity and in species evenness and heterogeneity measures, as indicated by Pairwise Euclidian distances and Morisita indices of community similarity. Our analyses suggest that human activities (i.e., deforestation for cattle ranching) coupled with environmental factors (i.e., increased precipitation) may have synergistically coalesced for an increased risk of HPS to area residents. Journal of Vector Ecology 29 (1): 177-191. 2004. Keyword Index: Calabazo virus, Choclo virus, Hantavirus ecology, Muridae, Panama, Sigmodontinae. INTRODUCTION Hantavirus pulmonary syndrome (HPS) is an increasingly recognized infectious disease associated with infection of humans by New World hantaviruses (family Bunyaviridae). The symptomatology of the disease, with a rapid onset of respiratory failure and a fatality rate of 38% to 69%, depending on the specific hantavirus, has been described extensively. Each hantavirus (small, tripartite, negative strand RNA virus) is usually hosted by a single species of rodent belonging to the murid subfamilies Sigmodontinae or Arvicolinae. Only hantaviruses associated with sigmodontine rodents are known to cause human disease in the Americas (15 of 20; Clement 2003). Transmission to humans occurs through inhalation of aerosolized excreta or saliva from infected rodents. In December 1999, cases clinically consistent with HPS began appearing in the Azuero region of Panamá, a