Spatial variation in abundance of the junin virus hosts in endemic and nonendemic Argentine haemorrhagic fever zones

Abstract

Argentine haemorrhagic fever (AHF) is caused by Junin (JUN) virus, which is hosted by the drylands vesper mouse (Calomys musculinus). In this work we monitored population abundance of C. musculinus and rodent assemblages for 3 years in and outside the AHF endemic zones (northern Buenos Aires, southern Córdoba and Santa Fe Provinces, Argentina). The study area was divided into endemic and nonendemic zones. In the endemic zone epidemic sites were recognized, characterized by recent emergence and maintenance of AHF cases, and also historical sites, characterized by decreased incidence or disappearance of AHF human cases. In the nonendemic zone AHF has never been recognized. Although differences were statistically significant only during some periods, population abundance of C. musculinus was usually lower in the nonendemic sites. The pattern and magnitude of seasonal fluctuations in C. musculinus populations were also distinct in the nonendemic sites as compared to endemic sites. The relative abundance of C. musculinus in rodent assemblage was lower in nonendemic sites than in the endemic sites. The lower population densities and dampened seasonal dynamics may be at least partly responsible for the absence of AHF cases in the nonendemic zone. It is suggested that the balance between intra and interspecific interactions might be the cause of the pattern of incidence and prevalence of pathogens in the host species.

Environmental determinants of the small mammal assemblage in an agroecosystem of central Argentina: The role of Calomys musculinus

“…Competition with A. azarae and, more in general, diversity of rodent community in borders may contribute to control C. musculinus population density and spatial continuity. These two factors are likely to be the main causes sustaining Junín virus maintenance and transmission (Polop et al 2007;Polop et al 2008). In this sense, in a diversified community, the number of intra-specific interactions may be reduced in favour of a greater number of interspecific contacts.…”

“…Arenaviruses are considered highly specific pathogens, for which non-host species do not contribute to the maintenance of the transmission chain. Thus, high diversity and abundance of non-host rodents can dilute the incidence of AHF on host species and subsequently reduce the human disease risk (Polop et al 2007). Ostfeld and Keesing (2000) termed a similar situation in the Lyme disease as 'the dilution effect'.…”

“…Indeed, the AHF has been historically characterized by seasonal outbreaks, coincident with the tillage period of aestival crops and also with C. musculinus population peaks (Mills et al 1992). The endemic area of AHF currently encompasses more than 150.000 Km 2 (Enría and Pinheiro 2000;Polop et al 2007). However, it includes only a small portion of the known and potential total distributional ranges of C. musculinus (Mills and Childs 1998;Porcasi et al 2005;Polop et al 2007).…”

“…Since Junín virus follows a horizontal transmission (Sabattini et al 1977), high population densities and, consequently, high contact rates between individuals are expected to be crucial for Junín virus maintenance and expansion in the population (Mills et al 1992;Begon et al 1998;Perkins et al 2009). Recently, Polop et al (2007) have suggested that also the proportional representation of C. musculinus in the overall rodent community may affect the efficiency of transmission of Junín virus. The potential inverse relationship between species diversity and disease transmission has long been recognized (Keesing et al 2006).…”

“…The endemic area of AHF currently encompasses more than 150.000 Km 2 (Enría and Pinheiro 2000;Polop et al 2007). However, it includes only a small portion of the known and potential total distributional ranges of C. musculinus (Mills and Childs 1998;Porcasi et al 2005;Polop et al 2007). AHF transmission risk may therefore expand, or at least modify substantially, in the future.…”