Prevalence of infection with hantavirus in rodent populations of central Argentina

We studied hantavirus seroprevalence and virus variability in rodent populations in Diego Gaynor, northwest of Buenos Aires province, Argentina. Rodent samplings were conducted in railroads and cropfield borders in March and July 1999, September and December 2000, and March 2001. Antibody detection was performed by an enzyme link immunosorbent assay (ELISA), using the recombinant nucleoprotein of Andes (AND) virus as antigen. Tissue samples were taken from positive antibody individuals in order to confirm the presence of hantavirus genomic material and to identify virus genotypes. Akodon azarae was the most abundant species, followed by Oligoryzomys flavescens, while Calomys laucha and C. musculinus were rarely caught. We found a rate of seroprevalence of 9.3% for a total sample of 291 A. azarae and 13.5% for 37 O. flavescens. After molecular analyses of hantavirus, we confirmed the presence of hantavirus genomic material in 16 individuals with ELISA (+) results and two individuals with ELISA (-). Four amplimers for each species were sequenced and compared to the corresponding sequences of representative hantaviruses. We identified the AND Cent Lec from three O. flavescens, and the Pergamino virus from four A. azarae and from one O. flavescens. A. azarae males had higher seroprevalence than females, and heavier individuals showed higher seroprevalence than lighter ones. We did not find seroprevalence differences according to sex in O. flavescens, although this result may have been produced by the low sample size. The lowest seroprevalence was found in a period of high rodent density, when juveniles prevailed in the population. We found higher seroprevalences than those detected in previous studies for other localities of central Argentina where cases of hantavirus pulmonary syndrome (HPS) have been reported. The presence of AND Cent Lec virus in rodent populations of the study area, which is responsible of HPS cases in central Argentina, suggests that human populations are at risk of HPS disease, although there were not reported cases of this disease until today.     

The molecular phylogenetics of the genus Oligoryzomys (Rodentia: Cricetidae) clarifies rodent host–hantavirus associations

Several species of the genus Oligoryzomys are natural hosts of different hantavirus genotypes affecting humans. The systematics of the genus is confusing, which complicates the identification of the rodent host and hence the potential endemic areas of hantavirus pulmonary syndrome. In this study, we analyse molecular data to infer phylogenetic relationships among Central and South American specimens of Oligoryzomys, and compare our results with previously published data on karyotypic, geographic distribution and host–virus associations to solve contradictory taxonomic reports. We identified 25 clades, each one corresponding to a different putative species. The phylogenetic trees show that Oligoryzomys longicaudatus is strongly related to the Oligoryzomys flavescens complex, which comprises four clades; Oligoryzomys nigripes is related to Oligoryzomys stramineus, Oligoryzomys vegetus is related to Oligoryzomys fulvescens from Central America, and Oligoryzomys brendae is the sister species of Oligoryzomys aff. destructor. We identified the following rodent host–hantavirus genotype relationships: O. longicaudatus–Andes; O. flavescens ‘West'–Bermejo; O. flavescens ‘East'–Lechiguanas; O. nigripes–Juquitiba; Oligoryzomys microtis–Rio Mamore and Rio Mamore‐3; Oligoryzomys chacoensis–Oran; Oligoryzomys costaricencis–Choclo; Oligoryzomys delicatus–Maporal; Oligoryzomys utiaritensis–Castelo dos Sonhos; Oligoryzomys sp. RT2012–Rio Mamore‐4; Oligoryzomys sp. (and not Oligoryzomys fornesi)–Anajatuba. This work, besides contributing to the development of prevention programmes for hantavirus epidemiology in Latin America, represents a comprehensive update of the systematics of the genus Oligoryzomys. © 2014 The Linnean Society of London     

Habitat preferences,seasonal abundance and diets of rodents in Alage,Southern Ethiopia

To understand habitat preferences, seasonal abundance and diets of rodents in wet and dry season surveys were conducted in Alage, Southern Ethiopia. Sherman and snap traps were used to capture rodents from the four habitats: bushland, Acacia woodland, maize and wheat farmlands. A total of 3312 trap nights, from the four trapping habitats, yielded 776 individuals that represented 11 species of rodents. The distribution of rodents varied between habitats and seasons. Wet season rodent abundance was 52.3% while in the dry season it was 47.7%. Seasonal differences in species abundance were insignificant. Bushland habitat had high wet and dry season abundances with 137 and 211 individuals, respectively. Abundance was low in maize farm (57 individuals) in the wet season and wheat farm (10 individuals) in the dry season. Stomach content composition analysis of snap‐trapped rodents from different habitats showed differences between species and across seasons. Six rodent species were recorded as pests on the farmlands in this study area. In conclusion, variation in habitat preferences and diet of rodents in different habitats and across seasons might be due to the role of ground cover and food sources.     

Ecological consequences of an unusual simultaneous masting of Araucaria araucana and Chusquea culeou in North‐West Patagonia,Argentina

A simultaneous masting of two abundant species in the temperate forests of North‐West Argentinean Patagonia occurred in 2013 for the first time ever recorded: the semelparous bamboo grass Chusquea culeou (colihue), dominating the understory, flowered and set seed across 1100 km² while pehuén (Araucaria araucana), an endemic conifer co‐dominating the tree layer had the highest regionally synchronized mast event in the last 30 years. Strong trophic effects were expected as a consequence of this extraordinary amount of seed, such as rodent outbreaks (ratadas) that followed previous Chusquea spp. mast events and included Oligoryzomys longicaudatus, the main reservoir of the Andes virus causing the Hantavirus Pulmonar Syndrome. From March 2013 to May 2014, we sampled relative abundance and activity of seed‐eaters and carnivores at four study sites with different proportions of both masting species. Surprisingly, total rodent capture rates never exceeded 14% in wild habitats and 8% in peridomestic areas showing low overall density in spite of some heavy O. longicaudatus males extending their reproductive activity into winter. Total abundance and relative proportion of granivorous birds peaked at the four sites in winter or spring, when they are usually scarce. Other surveyed organisms (native and exotic seed‐eaters, ungulates and carnivores) showed moderate responses at most, probably through aggregation from surrounding areas rather than reproduction. Seed removal from experimental seed stations varied in time and space though never peaked. The clearest pattern of community responses, though much subtler than expected, occurred at the site where colihue was abundant and pehuén scarce. This is the first systematic study that reports such a simultaneous double masting and our surveys revealed no widespread community consequences. We propose that either contingent events, such as an unprecedented drought, or permanent environmental features or contextual characteristics may explain the lack of a rodent outbreak in this area.     

Seasonal selectivity of Magellanic horned owl (Bubo magellanicus) on rodents

This study examines prey selection by Magellanic horned owls (Bubo magellanicus) in an ecotonal steppe area of northwestern Argentine Patagonia, and analyzes morphological and behavioral traits of the owls main rodent prey. The owls diet was studied for two years, along with field estimates of rodent abundance. The frequency distribution of rodents was significantly different from that estimated from trapping, indicating that Magellanic horned owl behaved as a selective predator. Eligmodontia morgani and Abrothrix xanthorhinus, the smallest species inhabiting open areas, were consumed in lower proportion than their occurrence estimated from the trapped sample, whereas the larger Abrothrix longipilis and Oligoryzomys longicaudatus, which inhabited bushy habitats, were eaten in a greater proportion than their estimated abundance. It is suggested that distinctive morphological and behavioral characteristics among prey interacting with the owl hunting strategy, accounted for their differential vulnerability to predation.     

Potential Geographic Distribution of Hantavirus Reservoirs in Brazil

Hantavirus cardiopulmonary syndrome is an emerging zoonosis in Brazil. Human infections occur via inhalation of aerosolized viral particles from excreta of infected wild rodents. Necromys lasiurus and Oligoryzomys nigripes appear to be the main reservoirs of hantavirus in the Atlantic Forest and Cerrado biomes. We estimated and compared ecological niches of the two rodent species, and analyzed environmental factors influencing their occurrence, to understand the geography of hantavirus transmission. N. lasiurus showed a wide potential distribution in Brazil, in the Cerrado, Caatinga, and Atlantic Forest biomes. Highest climate suitability for O. nigripes was observed along the Brazilian Atlantic coast. Maximum temperature in the warmest months and annual precipitation were the variables that most influence the distributions of N. lasiurus and O. nigripes, respectively. Models based on occurrences of infected rodents estimated a broader area of risk for hantavirus transmission in southeastern and southern Brazil, coinciding with the distribution of human cases of hantavirus cardiopulmonary syndrome. We found no demonstrable environmental differences among occurrence sites for the rodents and for human cases of hantavirus. However, areas of northern and northeastern Brazil are also apparently suitable for the two species, without broad coincidence with human cases. Modeling of niches and distributions of rodent reservoirs indicates potential for transmission of hantavirus across virtually all of Brazil outside the Amazon Basin.     

Hantaviruses: molecular biology, evolution and pathogenesis

Hantaviruses are tri-segmented negative sense single stranded RNA viruses that belong to the family Bunyaviridae. In nature, hantaviruses are exclusively maintained in the populations of their specific rodent hosts. In their natural host species, hantaviruses usually develop a persistent infection with prolonged virus shedding in excreta. Humans become infected by inhaling virus contaminated aerosol. Unlike asymptomatic infection in rodents, hantaviruses cause two acute febrile diseases in humans: hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). The mortality rate varies from 0.1% to 40% depending on the virus involved. Hantaviruses are distributed world wide, with over 150,000 HFRS and HPS cases being registered annually. In this review we summarize current knowledge on hantavirus molecular biology, epidemiology, genetic diversity and co-evolution with rodent hosts. In addition, special attention was given in this review to describing clinical manifestation of HFRS and HPS, and advances in our current understanding of the host immune response, treatment, and prevention.     

A long term study of small mammal populations in a Brazilian agricultural landscape

Long-term monitoring of small mammal populations is very important to understand the variations in temporal abundance on a large time scale, which are related to ecological, economic and epidemiological phenomena. The aim of this study is to monitor the populations of the marsupials Didelphis aurita and Philander frenatus and the rodents Nectomys squamipes, Akodon cursor and Oligorysomys nigripes in a locality of typical Brazilian rural landscape, Sumidouro Municipality, Rio de Janeiro State, Brazil. A mark-recapture study was conducted during five years. We analyzed the population dynamics, the reproduction and age structure of these species. Both marsupials presented higher population sizes in the end of wet period and beginning of the dry period, which can be explained by the seasonal reproduction which begins in the middle of the dry period and ends in the last months of the wet period. N. squamipes reproduced throughout the year but mostly during rainy periods, due to the close association of this rodent to resources found in the water. Higher survivorship and recruitment rates were in the end of the wet season. The rodent A. cursor had an opportunist reproduction, resulting in high turnover rates. Survivorship increased with the effects of the dry periods. O. nigripes showed a clear annual pattern of population cycle with peaks during the dry season. The rodents did not show potential to present outbreaks and become agricultural pests. The annual population cycles of O. nigripes and the unique peak of A. cursor population during five years highlight attention to their importance as wild reservoirs of the hantavirus disease. Their ecological characteristics associated to their opportunistic behavior make these species prone to be good reservoirs of zoonoses.     

Landscape partitioning by nocturnal rodent assemblages in the Llanos de Ojuelos,in Mexico’s Central High Plateau

Aim The Llanos de Ojuelos in Mexico’s Central High Plateau supports unique Opuntia scrublands and the southernmost Chihuahuan grasslands. Although human activities have modified strongly its landscape and impacted its biodiversity at an unknown scale, such impacts are poorly known. We aimed at understanding how nocturnal rodent species distributed across the landscape and formed assemblages and on the role and integration of the different habitats at the landscape level. Location The study was carried out at 43 sites in a study area of approximately 3350 km² in the Llanos de Ojuelos. Methods During the Spring of 2008, we surveyed nocturnal rodents, through live‐trapping. We redefined habitat classes based on log‐linear multinomial regressions of rodent captures. Species rarefaction curves and true alpha, beta and gamma diversities were calculated for the different habitat classes. A map of the different habitats was constructed based on Landsat imagery. Results We captured 458 individuals of 20 rodent species. Multinomial regressions caused the merger of 11 a priori defined habitat classes into 7. Leguminous scrub and mixed nopaleras, both secondary habitats, had the highest alpha and gamma diversity values. Closed arboreal nopaleras and grasslands had the highest within‐habitat variability (¹D_β) and the lowest area coverage. Within‐habitat ¹D_β was larger than landscape ¹D_β, because of the great overlap in rodent assemblage composition between the habitats. Main conclusions There are no ‘typical’ rodent assemblages per habitat class, but they are organized loosely and have fuzzy borders. Rodent community organization was highly species‐centred. At the landscape level, secondary habitats have a profound effect on rodent diversity and should be included in management schemes for biological conservation. The most endangered habitats seem to be the closed arboreal nopaleras and grasslands. Any conservation efforts must consider their conservation and an increase in the size of remaining patches.     

Microhabitat characteristics of Akodon montensis,a reservoir for hantavirus,and hantaviral seroprevalence in an Atlantic forest site in eastern Paraguay

Hantaviruses may cause serious disease when transmitted to humans by their rodent hosts. Since their emergence in the Americas in 1993, there have been extensive efforts to understand the role of environmental factors on the presence of these viruses in their host rodent populations. HPS outbreaks have been linked to precipitation, but climatic factors alone have not been sufficient to predict the spatial‐temporal dynamics of the environment‐reservoir‐virus system. Using a series of mark‐recapture sampling sites located at the Mbaracayú Biosphere Reserve, an Atlantic Forest site in eastern Paraguay, we investigated the hypothesis that microhabitat might also influence the prevalence of Jaborá hantavirus within populations of its reservoir species, Akodon montensis. Seven trapping sessions were conducted during 2005‐2006 at four sites chosen to capture variable microhabitat conditions within the study site. Analysis of microhabitat preferences showed that A. montensis preferred areas with little forest overstory and denser vegetation cover on and near the ground. Moreover, there was a significant difference in the microhabitat occupied by antibody‐positive vs antibody‐negative rodents, indicating that microhabitats with greater overstory cover may promote transmission and maintenance of hantavirus in A. montensis.     

Road-related landscape elements as a habitat: A main asset for small mammals in an intensive farming landscape

Road construction creates new habitats for a variety of species. In intensive farming landscapes, road verges may be the only suitable habitat for rodents. However, little attention has been paid to other road-related landscape elements (RRLEs), such as excavation slopes or the central islands of roundabouts, and their importance in a rodent territory. This study investigated all types of RRLE in terms of rodent abundances and habitat quality. RRLEs were compared with the semi-natural elements of the studied landscape using a capture-mark-recapture protocol. Four species and 3154 individuals were captured over a period of four months. Relative abundance and habitat quality were higher in RRLEs than in semi-natural elements. Mapping of the landscape showed that 86% of crop fields are accessible to Microtus arvalis (and almost 100% for Apodemus sylvaticus) from road verges. Our results highlight the importance of road verges and all other RRLEs in the conservation of species diversity in intensive farming landscapes.     

Space Use and Social Mating System of the Hantavirus Host, <Emphasis Type="Italic">Oligoryzomys longicaudatus</Emphasis>

The long-tailed mouse, Oligoryzomys longicaudatus (Cricetidae: Sigmodontinae), is the major host of Andes hantavirus, the etiological agent of hantavirus pulmonary syndrome in the south of Argentina and Chile. Studying the ecology of this species is necessary to understand how Andes hantavirus is maintained in nature. In this study, we examine the home range size and intra- and intersexual overlap degree of male and female O. longicaudatus in order to elucidate the mating system of this species. To our knowledge, this research provides the first documentation, obtained from a specific design, of spacing and mating systems in this species in Argentina. The study was conducted seasonally from April (autumn) 2012 to October (spring) 2013 in a shrubland habitat of Cholila, Andean region, Argentina. We studied spacing patterns using 59 and 51 home ranges established by adult males and females, respectively, in two 3.24 ha capture-marked and recapture grids. Significant differences between sexes in home range size and overlap degree were found. Male home ranges were always larger than those of females. We observed exclusive space use both among males and females (13.15 ± 18.67, and 3.60 ± 3.43%, respectively). Considering only those males that get access to receptive females (40%), average intersexual overlap value was about 30.82 ± 19.73%. Sexual differences in home range sizes and the spatial avoidance between breeding males, that would reflect intrasexual competition for receptive females, allows us to propose a polygynous mating system for O. longicaudatus.     

Ecology of a typical West African Sudanian savannah rodent community

The small‐mammal community of a typical Sudanian savannah area of south‐eastern Senegal was studied by way of intensive sampling at the beginning (July) and at the end (November) of the rainy season. A total of 5931 trapnights and 200 pitfallnights yielded 767 small mammals, including 757 rodents of 12 species, as well as a few shrews and hedgehogs. Accumulation curve indicated that the rodent community was well sampled. Murine rodents were far more numerous than gerbilline rodents, and among them, Mastomys erythroleucus was the dominant species, being caught in high numbers in all habitats. Arvicanthis niloticus and Praomys daltoni were also abundant, followed by Mastomys natalensis and Gerbilliscus guineae. Abundances were high at the beginning of the rainy season when reproductive activity was low in all species. At the end of the rainy season, murine rodents were actively involved in reproduction, while gerbilline rodents were at their lowest density. Significant changes in relative abundance among habitats (including human dwellings) were observed between periods in some species, suggesting seasonal trends in habitat preferences. This may help species coexistence in this species‐rich rodent community, in an area likely to be submitted to significant habitat alterations in the years to come.     

Occurrence rates of wild rodent hosts and chigger mites and the infection rate of Orientia tsutsugamushi in the central region of South Korea from 2015 to 2018

Outbreaks of vector‐borne diseases are dramatically increasing because of climate change, consequently increasing the importance of surveillance of endemic disease vectors. In this study, we surveyed chigger mites, vectors for Orientia tsutsugamushi—the bacteria that causes Tsutsugamushi disease—, and their rodent hosts in Gimcheon, central South Korea, in 2015–2018. A total of 225 rodents were collected, with trap rate and percentage of rodents infected by chigger mites of 9.8 and 72.4%, respectively. Six species of rodents from five genera were collected, the most common rodent being Apodemus agrarius (n = 153, infection rate = 90.8%). The highest number of rodents was collected in spring (trap rate = 10.3), but the rate of infected rodents was higher in fall (81.5%) than in spring (61.3%). Trap rate was highest for bank near waterway (17.9), but the chigger index (CI) was highest in hill (224.1). A total of 20,534 (CI 126.0) chigger mite individuals from 10 species and three genera were found on the collected rodents. The most common species was Leptotrombidium pallidum (n = 7,982, 83.6%, CI 49.0), followed by L. palpale and L. scutellare. Chigger mites were most frequent at banks near waterway (n = 11,093, CI 152.0) and hill (n = 2,017, CI 224.1). To detect O. tsutsugamushi in chigger mites, 450 pools of chigger mites (n = 10,991) were analyzed; 24 pools were positive—23 of A. agrarius, the most frequently collected species in South Korea, 1 of Micromys minutus—and the minimum positive rate (MPR) was 0.22. The detected strain types included Boryong (dominant in all years, seasons, and habitats), Jecheon, 07–489, and IIOC1202.     

洞庭湖洲滩及滨湖区鼠类分布格局及其多样性

为全面了解洞庭湖洲滩及滨湖区鼠类分布格局,统计自2003—2013年该湖区15个调查点5种不同生境的鼠类群落调查数据,并对鼠类群落的物种多样性进行分析。结果表明:2003—2013年洞庭湖区捕获鼠类有10种,主要优势种为黑线姬鼠(Apodemus agrarius)和东方田鼠(Microtus fortis);不同生境下的优势种不同,东方田鼠为湖滩生境优势种,黑线姬鼠是滨湖农田和退田还湖洲滩生境优势种,针毛鼠(Niviventer fulvescens)和社鼠(Niviventer confucianus)为滨湖丘岗林地优势种,小家鼠(Mus musculus)及黄胸鼠(Rattus tanzumi)则多出现在农房生境;不同生境的鼠类群落物种多样性不同,滨湖丘岗林地生境受人类活动或洪水干扰程度最低,因此,优势集中性指数最低,而物种多样性Shannon-Wiener指数在干扰较少的滨湖丘岗林地生境物种多样性指数最高。尽管湖滩生境受三峡工程的影响,物种数大量增加,但由于仍受汛期洪涝的干扰,依然具有优势种突出的特征。研究表明,人类社会活动或洪涝等干扰因素降低了鼠类群落物种多样性,致使优势种突出,形成只利于少数几个种群栖息的环境,最终导致种群大暴发。     

Species composition,abundance and habitat association of rodents and insectivores from Chilalo–Galama Mountain range,Arsi, Ethiopia

A study on the ecology of rodents and insectivores on Mount Chilalo and the Galama Mountain range was conducted during August, 2007–April, 2008. Study grids were marked in nine randomly selected habitats. Sherman live traps and snap traps were used to capture the small mammals. A total of 2525 (including recaptures) individual rodents and insectivores were captured in 5488 (Sherman) and 1590 (snap) trap‐nights. Among the live‐trapped animals, 2037 (96.2%) and 80 (3.8%) were rodents and insectivores, respectively, that comprised 17 species. These were as follows: Arvicanthis abyssinicus, Arvicanthis blicki, Arvicanthis dembeensis, Lophuromys flavopunctatus, Lophuromys melanonyx, Mastomys natalensis, Mus mahomet, Otomys typus, Rattus rattus, Stenocephalemys albipes, Stenocephalemys albocaudata, Stenocephalemys griseicauda, Crocidura glassi, Crocidura flavescens and Crocidura thalia. Tachyoryctes splendens and Hystrix cristata were sighted but not captured. Endemics to Ethiopia constituted 60% of the trapped small mammals. Lophuromys flavopunctatus was the most abundant and widely distributed rodent species, while M. mahomet was the least. The altitudes between 3301 and 3400 m asl had the highest species composition and abundance although it is second in number of catches per trap‐nights. The majority of rodents and insectivores were associated with montane forest habitat, whereas the least were in the shrubland. Anthropogenic effects were witnessed affecting the distribution of small mammals.     

贺兰山西坡啮齿动物生境选择及种间关系

为明确对贺兰山西坡啮齿动物生境选择起关键作用的主要环境因子,探讨各鼠种之间的相互作用如何影响鼠种的生境选择,选取地理因子（海拔、坡度、坡向）、植被因子（植被盖度、植被高度、灌木/乔木高度）和其他因子（距水源距离、距道路距离、距灌木/乔木距离）等9种生境因子,利用资源选择函数模型和logistic回归模型对啮齿动物生境选择和种间关系进行分析。结果表明,在贺兰山西坡,捕获数量最多的6种啮齿动物对的生境选择存在差异,大林姬鼠（Apodemus peninsulae）偏好高海拔、多灌木（乔木）的生境;子午沙鼠（Meriones meridianus）偏好海拔较低的半荒漠稀疏生境,对道路和人为干扰不回避;灰仓鼠（Cricetulus migratorius）偏好距水源较远、多灌木（乔木）、距道路较近的生境;阿拉善黄鼠（Spermophilus alaschanicus）偏好低海拔、植被丰富的生境;短尾仓鼠（Cricetulus eversmanni）偏好高海拔、距道路较近的生境;社鼠（Niviventer niviventer）偏好海拔较高、坡度较大、距水源较远的生境。鼠种间的相互关系主要呈现回避或随机关系。研究结果有助于了解啮齿动物分布的变化及种群动态规律,可为贺兰山生物资源保护,区域性鼠害的预测、预报和综合治理提供基础资料和科学依据。     

Bayou virus detected in non‐oryzomyine rodent hosts: an assessment of habitat composition,reservoir community structure,and marsh rice rat social dynamics

In the United States, Bayou virus (BAYV) ranks second only to Sin Nombre virus (SNV) in terms of hantavirus pulmonary syndrome (HPS) incidents, having been confirmed in cases from Texas and Louisiana since its discovery in 1994. This study on BAYV infection among sympatric, non‐oryzomyine rodents (“spillover”) in Freeport, TX, is the first to link patterns of hantavirus interspecific spillover with the spatiotemporal ecology of the primary host (marsh rice rat, Oryzomys palustris). Mark‐recapture and/or harvest methods were employed from March 2002 through May 2004 in two macrohabitat types. Rodent blood samples were screened for the presence of IgG antibody to BAYV antigen by IFA after which Ab‐positive blood, saliva, and urine were analyzed for the presence of viral RNA by nested RT‐PCR. From 727 non‐oryzomyine captures, five seropositive (but not viral RNA positive) individuals were detected: one each of Baiomys taylori, Peromyscus leucopus, and Reithrodontomys fulvescens; and two Sigmodon hispidus. Spillover hosts were not associated with macrohabitat where O. palustris abundance, density, or seroprevalence was highest. Rather, spillover occurred in the macrohabitat indicative of greater overall disturbance (as indicated by grazing and exotic plant diversity) and overall biodiversity. Spillover occurred during periods of high seroprevalence detected elsewhere within the study region. Spillover locations differed significantly from all other capture locations in terms of percent water, shrub, and grass cover. Although greater habitat and mammal diversity of old‐fields may serve to reduce seroprevalence levels by tempering intraspecific contacts between rice rats, greater diversity also may create an ecologically opportunistic setting for BAYV spillover. Impacts of varying levels of disturbance and biodiversity on transmission dynamics represent a vastly uncharacterized component of the evolutionary ecology of hantaviruses.     

Transmission study of Andes hantavirus infection in wild sigmodontine rodents

Our study was designed to contribute to an understanding of the timing and conditions under which transmission of Andes hantavirus in Oligoryzomys longicaudatus reservoir populations takes place. Mice were caged in test habitats consisting of steel drums containing holding cages, where seronegative rodents were exposed to wild seropositive individuals by freely sharing the same cage or being separated by a wire mesh. Tests were also performed for potential viral transmission to mice from excrement-tainted bedding in the cages. Andes virus transmitted efficiently; from 130 attempts with direct contact, 12.3% resulted in virus transmission. However, if we consider only those rodents that proved to be infectious, from 93 attempts we obtained 16 infected animals (17.2%). Twelve of them resulted from intraspecies O. longicaudatus encounters where male mice were differentially affected and 4 resulted from O. longicaudatus to Abrothrix olivaceus. Experiments using Abrothrix longipilis as receptors were not successful. Transmission was not observed between wire mesh-separated animals, and mice were not infected from excrement-tainted bedding. Bites seemed not to be a requisite for oral transmission. Genomic viral RNA was amplified in two out of three saliva samples from seropositive rodents, but it was not detected in urine samples obtained by vesicle puncture from two other infected rodents. Immunohistochemistry, using antibodies against Andes (AND) hantavirus proteins, revealed strong reactions in the lung and salivary glands, supporting the possibility of oral transmission. Our study suggests that AND hantavirus may be principally transmitted via saliva or saliva aerosols rather than via feces and urine.     

Seed bank dynamics of the desert cactus Opuntia rastrera in two habitats from the Chihuahuan Desert

In desert environments the main input to the seed bank of many succulents is the seed rain through zoochory while high levels of granivory by rodents, birds and ants are the main cause of subsequent losses. In the patchy environment of arid lands the characteristics of both processes may vary between habitats causing differences in the recruitment of new genets. To test this hypothesis we used populations of the desert cactus Opuntia rastrera which has different recruitment rates in the two adjacent habitats where it grows. In Opuntia-dominated scrublands (nopaleras, density ca. 4,000 plants/ha) 1 seedling out of 7,000,000 seeds establish, whereas in grasslands (density ca. 100 plants/ha) this ratio is 1:20,000. From 1996 until 1998 the seed rain, seed removal by granivores and seed abundance in the soil were monitored in both habitats. Results showed striking differences in the dynamics of the seed bank of both habitats. Seed rain was 8.5 times bigger in nopaleras than in grasslands. In nopaleras most seeds were removed by rodents while the quantities of seeds removed by rodents, birds and ants in grasslands were similar. One year after dispersal (the time necessary to break seed dormancy) only 6% of original nopalera seeds and 12% of grassland seeds remained. After germination trials only 1% (ca. 15,000 seeds/ha) and 2% (ca. 2,500 seeds/ha) respectively were viable. These differences in the effective seed bank (6 times bigger in nopaleras) can not explain the differences in genet recruitment (which is several orders of magnitude bigger in grasslands). Apparently the between habitat difference in nurse plant availability and in rodent density (which inflict a strong hervibory upon seedlings) can explain the differences in genet recruitment. It is speculated that this between habitat difference in genet recruitment suggests that the species evolved in less extreme environments (e.g. grasslands) than desert scrublands which, in turn, are colonised due to the singular ability of O. rastrera for vegetative propagation. This revised version was published online in August 2006 with corrections to the Cover Date.