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Habitat fragmentation and diversity loss due to increased conversion of natural habitats to agricultural uses influence the distribution and abundance of wildlife species and thus may change the ecology of pathogen transmission. We used hantaviruses in Panama as a research model to determine whether anthropogenic environmental change is associated with changes in the dynamics of viral transmission. Specifically, we wanted to determine whether hantavirus infection was correlated with spatial attributes of the landscape at both large and small scales or whether these changes are mediated by changes in community composition. When analyzed at coarse spatial scales, hantavirus reservoirs were more commonly found in disturbed habitats and edge habitats than in forested areas. At local scales, reservoir species dominance was significantly correlated with the slope of the terrain. To evaluate the effect of small-mammal diversity loss on infection dynamics, we implemented an experiment with selective species removal at experimental sites. Seroprevalence of hantavirus was higher in the community of small mammals and increased through time in the experimental sites. The higher seroprevalence in experimental plots suggests that greater diversity likely reduces encounter rates between infected and susceptible hosts. Our studies suggest that habitat loss and fragmentation and species diversity loss are altering hantavirus infection dynamics in Panama. Our work represents a multidisciplinary approach toward disease research that includes biodiversity concerns such as environmental change and degradation, human settlement patterns, and the ecology of host and nonhost species, work that may be especially important in tropical countries. [ABSTRACT FROM AUTHOR]

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Hantavirus cardiopulmonary syndrome (HCPS), which is caused by infection with Choclo virus, is uncommon in Panama, yet seropositivity among rural residents is as high as 60%. To clarify the environmental risk factors favoring rodent-to-human transmission, we tested serum from 3,067 rodents captured over a five-year period for antibodies against recombinant N protein of hantavirus by enzyme immunoassay and strip immunoblot. Among 220 seropositive rodents, Oligoryzomys fulvescens, the reservoir of Choclo virus, had the highest overall seroprevalence (23.5%); more abundant rodents (Zygodontomys brevicauda and Sigmodon hirsutus) had lower seroprevalences. In the mixed (combined modern and traditional) productive agroecosystem, the highest seroprevalence was among O. fulvescens captured in residences and in crops grown within 40 meters of a residence, with significantly lower seroprevalence in adjacent pasture and non-productive vegetation. Thus, crop habitats may serve as refugia for invasion into adjacent human residences and suggests several interventions to reduce human infection.

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.

Five hundred fifty-six samples representing 24 species of small mammals (two species of marsupials and 22 rodents) were collected in Panama between February 2000 and July 2002. The samples were examined for antibodies to hantaviruses by means of enzyme-linked immunosorbent assay or immunoblot assays. The serologic results indicated that several rodent species might act as hantaviral reservoirs in Panama: Costa Rican pygmy rice rat (Oligoryzomys fulvescens costaricensis), four positive of 72 tested (5.6%); Cherrie's cane rat (Zygodontomys brevicauda cherriei), five of 108 (4.6%); Mexican deer mouse (Peromyscus mexicanus), one of 22 (5%); Mexican harvest mouse (Reithrodontomys mexicanus), one of seven (14%); Chiriquí harvest mouse (Reithrodontomys creper), one of two (50%); and Sumichrast's harvest mouse (Reithrodontomys sumichrasti), three of four (75%). Hantavirus infection in Peromyscus mexicanus and the three species of Reithrodontomys was caused by Rio Segundo hantavirus, a species of virus not previously reported from Panama. At least three hantaviruses, therefore, are known to infect populations of wild rodents in the country. However, given the total number of animals tested, the role of these rodent species in the epidemiology and epizootiology of hantavirus infections remains unclear.