Distributional ecology of Andes hantavirus: a macroecological approach

Abstract

Background: Hantavirus pulmonary syndrome (HPS) is an infection endemic in Chile and Argentina, caused by Andes hantavirus (ANDV). The rodent Oligoryzomys longicaudatus is suggested as the main reservoir, although several other species of Sigmodontinae are known hosts of ANDV. Here, we explore potential ANDV transmission risk to humans in southern South America, based on eco-epidemiological associations among: six rodent host species, seropositive rodents, and human HPS cases.

Methods: We used ecological niche modeling and macroecological approaches to determine potential geographic distributions and assess environmental similarity among rodents and human HPS cases.

Results: Highest numbers of rodent species (five) were in Chile between 35° and 41°S latitude. Background similarity tests showed niche similarity in 14 of the 56 possible comparisons: similarity between human HPS cases and the background of all species and seropositive rodents was supported (except for Abrothrix sanborni). Of interest among the results is the likely role of O. longicaudatus, Loxodontomys micropus, Abrothrix olivaceus, and Abrothrix longipilis in HPS transmission to humans.

Conclusions: Our results support a role of rodent species' distributions as a risk factor for human HPS at coarse scales, and suggest that the role of the main reservoir (O. longicaudatus) may be supported by the broader rodent host community in some areas.

Keywords: Andes hantavirus; Bunyaviridae; Ecological niche modeling; Maxent; Rodent reservoirs; Zoonoses.

Fig. 1

Ecological niche models for rodent hantavirus hosts, seropositive rodents, and human HPS cases. Orange areas depict potential distributions based on ecological niche models. Blue areas show the study area M for model calibration. These binary maps were generated based on an acceptable omission rate of 5%

Fig. 2

Temperature and precipitation tolerances derived from niche models for six species of rodent hosts, infected rodents, and human HPS cases, based on ecological niche models. Boxplot figures depict precipitation (in mm) and temperature (in  °C degrees) intervals occupied by each species or group analyzed

Fig. 3

Rodent species richness (number of species predicted by cell). Chile and Argentina, divided by Regions (Chile) and Provinces (Argentina). Areas of high (dark red) to low (light pink) richness of rodent hosts were identified according to ecological niche model predictions. Values represent the number of rodent species by pixel as predicted by the ecological niche models

Fig. 4

Ecological niche similarity tests: a Background similarity tests were developed in a series of two-way comparisons. Occurrences (y-axis) were compared against the backgrounds of each other species (x-axis). Gray fill indicates that the null hypothesis of no difference between niches was not rejected (p > 0.05), and white squares denote hypothesis rejected; b Convex polyhedrons derived from occurrences of each rodent species (yellow) and human HPS cases (red) in a multidimensional environmental space (principal components 1, 2, and 3, obtained from the original bioclimatic layers). Note that the environmental space occupied by human cases are contained within the set of environments used by the rodent species

Fig. 5

Hantavirus ecological niche model visualized in environmental space. Model predictions of human HPS cases (red) and seropositive rodents (green) displayed in a multidimensional environmental space (principal components 1, 2, and 3 obtained from the original bioclimatic layers). Note the considerable overlap of environments occupied by human cases and hantavirus seropositive rodents. This suggests that the presence of seropositive rodents may explain and predict spillover events (transmission of hantavirus from rodents to humans)

Fig. 6

Proposed framework for the hantavirus system. The figure illustrates three scales (rectangles) of hantavirus occurrence. The reservoir’s niche comprises the set of abiotic environmental conditions required by each of the rodent species to maintain populations in the long term (light green circle). Hantavirus’ niche is the set of suitable abiotic environmental conditions necessary for hantavirus at coarse (e.g., climate) and fine scales (e.g., host internal temperature; dark green circle). Finally, a “niche” may characterize conditions apt for transmission to humans: sites where rodents and hantavirus co-occur, and in which susceptible humans are able to be infected (red circle). Elements influencing gaps between scales are shown in italics. At the right, elements that may affect overall processes