Argentine hemorrhagic fever (AHF) is a serious endemic disease in Argentina, produced by Junín virus, whose host is the Sigmodontinae rodent . Within the endemic area, human incidence and proportion of infected rodents remains high for 5-10 years after the first appearance of the disease (epidemic [E] zone) and then gradually declines to sporadic cases (historic [H] zone). We tested the hypothesis that host populations within the E zone are large and well connected by gene flow, facilitating the transmission and maintenance of the virus, whereas those in the H and nonendemic (NE) zones are small and isolated, with the opposite effect. We estimated parameters affected by levels of gene flow and population size in 14 populations of: population effective size (), genetic variability, and mean relatedness. Our hypothesis was not supported: the lowest levels of variability and of and the highest genetic relatedness among individuals were found in the H zone. Populations from the NE zone displayed opposite results, whereas those in the E zone showed intermediate values. If we consider that populations are first NE, then E, and finally H, a correlative decrease in was observed. Chronically infected females have a low reproductive success. We propose that this would lower because each cohort would originate from a fraction of females of the previous generation, and affect other factors such as proportion of individuals that develop acute infection, probability of viral transmission, and evolution of virulence, which would explain, at least partly, the changing incidence of AHF.
We evaluate several management options for Calomys musculinus populations through the formulation and validation of a cohort structured model. Initially, a basic model was constructed and validated using field population data. Next, the model was altered to allow us to evaluate different management options. In general, basic model results were in agreement with field data, demonstrating that this model would be useful in describing aspects of corn mouse population dynamics. Restricting control measures to when mouse numbers reach high levels would be inadequate, because population numbers tend to increase in size after some years. In contrast, reducing vegetation cover in spring was more effective in reducing field population abundances. Despite some limitations, the model could be useful for evaluating the relationships between population dynamics and some biotic or physical environmental variables, and thus ensure more efficient use of resources in integrated pest management.
Background. The Argentine Hemorrhagic Fever (AHF) is a zoonotic disease endemic in a wide area of the humid pampa of Argentina. The etiologic agent is the Junin virus that is maintained in the wild by the rodent Calomys musculinus and transmitted to humans, mainly, through aerosols generated from secretions and excretions. Aims: To characterize and compare the assemblages of small rodent composition and diversity inside the epidemic, historic and non-endemic zone of AHF and to register C. musculinus abundance in each zone and in each area within each zone, registering the prevalence of infection in rodent populations. Method: One central and two peripheral areas were delimited to sample rodents in each zone with different incidence of AHF. Thus, 18 localities were selected to do the sampling in two years. Host abundance between zones and among areas inside each zone and among nearby areas between zones were compared applying nested ANOVA's. Results: In each zone, the rodent assemblage showed differences in composition, diversity and numeric representation of C. musculinus. The epidemic zone was the richest of the three, registering also great host abundance; meanwhile in the historic zone, A. azarae was the dominant numeric species with less number of other species. Regarding the non-endemic zone, the assemblage composition and C. musculinus abundance varied respect the sampled year. Junin virus infection was only detected in C. musculinus individuals corresponding to the epidemic zone, with a prevalence of 2.7 and 1.1% for the years 2007 and 2008, respectively. Conclusion: In this system, the abundance of C. musculinus could be impacting over the pathogen dynamic, rather than the assemblage diversity or the A. azarae presence.
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