Evaluation of habitat requirements of small rodents and effectiveness of an ecologically‐based management in a hantavirus‐endemic natural protected area in Argentina

Hantavirus pulmonary syndrome is a severe cardio pulmonary disease transmitted to humans by sylvan rodents found in natural and rural environments. Disease transmission is closely linked to the ecology of animal reservoirs and abiotic factors such as habitat characteristics, season or climatic conditions. The main goals of this research were: to determine the biotic and abiotic factors affecting richness and abundance of rodent species at different spatial scales, to evaluate different methodologies for studying population of small rodents, and to describe and analyze an ecologically‐based rodent management experience in a highly touristic area. A 4‐year study of small rodent ecology was conducted between April 2007 and August 2011 in the most relevant habitats of El Palmar National Park, Argentina. Management involved a wide range of control and prevention measures, including poisoning, culling and habitat modification. A total of 172 individuals of 5 species were captured with a trapping effort of 13 860 traps‐nights (1.24 individuals/100 traps‐nights). Five rodent species were captured, including 2 hantavirus‐host species, Oligoryzomys nigripes and Akodon azarae. Oligoryzomys nigripes, host of a hantavirus that is pathogenic in humans, was the most abundant species and the only one found in all the studied habitats. Our results are inconsistent with the dilution effect hypothesis. The present study demonstrates that sylvan rodent species, including the hantavirus‐host species, have distinct local habitat selection and temporal variation patterns in abundance, which may influence the risk of human exposure to hantavirus and may have practical implications for disease transmission as well as for reservoir management.     

Associations between leptospiral infection and seropositivity in rodents and environmental characteristics in Argentina

Our objective was to look for associations between leptospiral infection in rodents and selected environmental and rodent characteristics in Santa Fe, Argentina. Rodents (n = 214) were trapped alive from January 1998 to December 1999 in three environmental settings. Kidneys from 118 rodents were cultured and serum samples from 201 were processed by enzyme-linked immunosorbent assay (ELISA). Logistic regression was performed with ELISA seropositivity as the dependent variable and rodent characteristics were offered as independent variables. Overall prevalence of positive ELISA reactions was 42% (84/201). In urban areas, leptospiral isolations belonged to the Ballum serogroup; in natural corridors, they belonged to the Icterohaemorragiae serogroup. M. musculus (house mouse) was the most-frequently captured species and the predominant one in urban areas. Most isolates and seropositivity results were obtained on this species. Adults and subadults had higher seroprevalences than juvenile rodents. Oligoryzomys flavescens had higher seroprevalence than Akodon azarae, Mus musculus, Rattus rattus and Rattus norvegicus.     

Filling the gaps in the Argentinian distribution of orthohantavirus: First finding of Lechiguanas virus in rodents from Corrientes,Argentina

Hantavirus Pulmonary Syndrome (HPS) is an emerging infectious disease caused by orthohantaviruses in the Americas. In Argentina, since 1995, several reservoirs and virus variants have been described, but the northeastern and central endemic zones in the country include an area without human or rodent infections, despite sharing rodent species with areas with that disease. The aim of this study was to search for orthohantavirus in rodent communities that inhabit this area, which borders two endemic areas of HPS. Small rodents were captured in June of 2022 through a total effort of 644 trap nights distributed in five grids located in the Iberá National Park, Corrientes, Northeastern Argentina. All rodents were sexed, weighed, and the species was recorded. Blood samples were extracted to detect ANDV-specific immunoglobulin G (IgG), and to extract the RNA virus. Trimmed sequences were mapped against reference sequences from GenBank. We captured a total of 36 Oligoryzomys flavescens and 15 Oxymycterus rufus. We detected the O. flavescens species infected with Lechiguanas orthohantavirus in the camping area of the National Park. A nucleotide comparison with previously published sequences shows a 98.34% similarity to the virus obtained from a human case of HPS reported in the adjacent Misiones province. This study demonstrated, for the first time, that O. flavescens is a host of the Lechiguanas orthohantavirus in this zone and contributes to closing information gaps on the distribution of orthohantavirus in Argentina. Additionally, the high similarity with the hantavirus found in the human case of Misiones suggests that the reservoir in that province would also be O. flavescens (not previously confirmed). This information permits us to focus on the preventive measurements to protect the human population.     

Home range variability,spatial aggregation,and excursions of Akodon azarae and Oligoryzomys flavescens in Pampean agroecosystems

Rodents are reservoirs of various types of hantavirus, some of which are agents of hantavirus pulmonary syndrome in humans. Each hantavirus is associated with a single rodent host species but successive spill‐over events may eventually lead to host‐switching and new species’ becoming host of a given pathogen. This study aims to gain an understanding of the spatial ecology of two hantavirus‐host species, Akodon azarae, and Oligoryzomys flavescens, by identifying factors modulating their home range sizes and stability, and by evaluating intra‐ and interspecific spatial aggregation for these species and a third one—Oxymycterus rufus—living in sympatry. For this, eleven capture‐mark‐recapture surveys were carried out, spanning 22 months. We found that A. azarae males have larger and more mobile home ranges than females, independently of the season. Consequently, males could likely have a more relevant role in the transmission of hantavirus because of their greater exposure both to a higher number of contacts between individuals and viral contamination of the environment. Contrasting, O. flavescens individuals showed negligible displacements of their home range through time, which could limit the range of hantavirus spread in host populations. Since O. flavescens is host to Lechiguanas hantavirus (pathogenic to humans) this result encompasses epidemiological relevance, for it may imply the existence of local foci of infection. Additionally, individuals of both species performed excursions outside their home ranges. These events could enable hantavirus spread over distances beyond the normal range of movements and lead to new hantavirus outbreaks in formerly non‐infected rodent populations, favoring the persistence of the virus in nature.     

Effects of exposure to environmental chemicals during pregnancy on the development of the male and female reproductive axes

There is a large body of literature describing effects of environmental chemicals (ECs), many of them anthropogenic with endocrine-disrupting properties, on development in rodent laboratory species, some of which lead to impaired reproduction and adverse health. This literature joins extensive human epidemiological data and opportunistic wildlife findings on health effects of ECs. In contrast, the effect of endocrine disruption on foetal development and reproductive performance in domestic species is less extensively documented. This applies both to domestic farm and to companion species even though the former is critical to food production and the latter share our homes and many aspects of the modern developed human lifestyle. In domestic species, the nature of chemicals exposure in utero and their consequences for animal health and production are poorly understood. A complication in our understanding is that the pace of development, ontogeny and efficiency of foetal and maternal hepatic and placental activity differs between domestic species. In many ways, this reflects the difficulties in understanding human exposure and consequences of that exposure for the foetus and subsequent adult from epidemiological and largely rodent-based data. It is important that domestic species are included in research into endocrine disruption because of their (i) wide variety of exposure to such chemicals, (ii) greater similarity of many developmental processes to the human, (iii) economic importance and (iv) close similarities to developed world human lifestyle in companion species.     

Seasonal dynamics and hosts of Amblyomma triste (Acari: Ixodidae) in Argentina

The seasonal dynamics and host usage of Amblyomma triste in Argentina were analyzed. Adults of A. triste were present from early winter to mid-summer, with the peak of abundance from late winter to mid-spring (August to October). Larvae and nymphs were found from December to June, with the peak of abundance in summer. There were no differences among the biological parameters (pre-moult period of larvae and nymphs, pre-oviposition period of females, and minimum incubation period of eggs) of engorged ticks exposed to different photoperiod regimens at the laboratory, but the periods for each biological parameter obtained from ticks exposed in the field were significantly longer than those from the laboratory. Field results fit better with the data of seasonal distribution of each stage. Morphogenetic diapause was not detected, but complementary studies should test the presence of behavioral diapause. Rodents of the subfamily Sigmodontinae (Akodon azarae, Oligoryzomys flavescens, Oligoryzomys nigripes, Oxymycterus rufus and Scapteromys aquaticus) are the principal hosts for immature stages of A. triste, the caviid Cavia aperea could be another potential host for these stages, and birds are exceptional hosts for larvae and nymphs. Regarding hosts of adults in Argentina, domestic and wild large-sized mammals belonging to different orders (cattle, dog, horse, Blastocerus dichotomus and Hydrochoerus hydrochaeris) serve as hosts for adults of this tick species. In conclusion, A. triste has a life cycle of 1 year with adults feeding on large endemic and introduced mammals and immature stages using sigmodontine and caviid rodents as hosts.     

New data about home range and movements of Oligoryzomys flavescens (Rodentia: Cricetidae) help to understand the spread and transmission of Andes virus that causes Hantavirus Pulmonary Syndrome

Hantavirus pulmonary syndrome is an emerging infectious disease caused by viruses of the genus Orthohantavirus. The rodent Oligoryzomys flavescens is distributed along four countries of South America. In Argentina, O. flavescens acts as a reservoir of three genotypes of ANDV orthohantavirus. The aims of this work were to estimate home range size and movements—with spool‐and‐line and radiotelemetry—of infected and non‐infected O. flavescens in order to understand the spread and transmission of the virus. O. flavescens use a wide area to satisfice its requirements, reaching a home range of 1.82 ha during spring. Orthohantavirus infection did not change the behaviour of individuals. We observed a great overlapping in the home range of infected and non‐infected individuals resulting in a high probability of virus dispersion on rodent population. These results show that human health risks could be high on island environments and knowledge about the movement ecology of O. flavescens provides useful information on prevention.     

典型草原鼠类群落结构研究

2007～2011年在锡林郭勒典型草原示范区(东乌珠穆沁旗恩和宝力格苏木)和对照区(锡林浩特市阿尔善宝力格苏木),对鼠类数量变动进行了监测。结果表明:对照区鼠类群落鼠种数多于示范区;对照区不同年份占群落捕获量比例较大的鼠种不同,而示范区大部分年份占群落捕获量比例较大的鼠种为黑线毛足鼠;对照区易形成危害的布氏田鼠数量2007年较高的时候,示范区相对低,仅在2007年9月出现,且该月布氏田鼠和黑线毛足鼠数量较为接近;对照区优势鼠种为布氏田鼠,示范区优势鼠种为黑线毛足鼠和长爪沙鼠;对照区短耳仓鼠和草原鼠兔呈极显著正相关,示范区布氏田鼠与五趾跳鼠呈极显著正相关;对照区5年中多样性指数、均匀性指数、丰富度指数各年变化的大小顺序一致,且均与优势度指数各年变化的大小顺序相反,而示范区5年中多样性指数分别与均匀性指数和丰富度指数各年变化的大小顺序不一致,且仅多样性指数与优势度指数各年变化的大小顺序相反。     

碌曲县啮齿动物种类组成

2008-2011年,在实施“碌曲县草原鼠害综合防治——县级示范点建设”项目的过程中,对该县啮齿动物种类组成与分布情况进行了调查研究。已查明在碌曲县共有38种啮齿类动物,隶属于6科7亚科19属。碌曲县土地面积仅占甘南州土地面积的13.18%,但啮齿动物种数却占全州啮齿动物种数的74.51%,表明碌曲县的生境条件和鼠种类组成在甘南州具有一定的代表性。以草原啮齿动物（60.53%）和森林啮齿动物（26.32%）为主体是碌曲县啮齿动物种类组成的基本特征。     

川西北高原鼠荒地危害程度分级及适应性管理对策

高原鼠兔和高原鼢鼠是青藏高原特有的食草型小动物,其啃食、掘洞、刈割、贮草行为对高寒草甸生态系统既具有破坏损伤系统的负面效应,也有利于维持和稳定系统的正面效应,这种益害转化完全取决于不同时间和空间尺度上的害鼠种群及其数量。通过对川西北的阿坝州、甘孜州和青海省果洛州的42个高寒草地样地的鼠类种群密度调查和已有文献的采集分析,明确了草原害鼠在高寒草地生态系统中的角色和作用,定义了鼠荒地的概念,对鼠荒地危害程度划分为轻度、中度、重度和极度4个等级;依据指标因子重要性排序,分级指标包含害鼠种群、植物群落和土壤养分3个主因子群;总洞穴数量、有效洞口数等11个单项因子;并对不同危害程度的鼠荒地提出了封育自然修复、人为干预修复、半人工草地改建和人工草地重建4种草原鼠害适应性管理策略,对于高寒草地生态系统草原害鼠适应性管理和害鼠灭除后二次发生防控具有指导意义。     

基于MapGIS平台的阿拉善荒漠区啮齿动物群落专家系统中推理机的研究与实现

本研究在前期研发阿拉善荒漠区啮齿动物群落专家系统的基础上，对开垦、轮牧和过牧3种不同类型生境中啮齿动物优势种子午沙鼠(Meriones meridianus)、三趾跳鼠(Dipus sagitta)和小毛足鼠(Phodopus roborovskii)相对数量与8个不同植物因子动态关系进行定量非线性分析，借助MapGIS平台，利用3种优势啮齿动物种群相对数量与8个不同植物因子组成的数据库系统、3种优势啮齿动物种的图像信息组成的知识库系统、3种不同生境下19种不同生态模型组成的模型库系统，构成啮齿动物群落中种群相对数量与植物因子动态关系的推理机，通过程序设计语言VB (Visual Basic)进行MapGIS二次开发，在专家系统中予以设计并实现。     

Experimental evidence of host specificity of Bartonella infection in rodents

A large number of Bartonella species and genetic variants were compared for their ability to cause bacteremia in different rodent species: the cotton rat (Sigmodon hispidus), white-footed mouse (Peromyscus leucopus), BALB/c mouse and Wistar rat. Experimental data supported field observations that host specificity can occur among certain Bartonella species and rodent species. Bacteremia could only be readily produced in cotton rats or white-footed mice if the strains used for inoculation were originally obtained from the same species or from a phylogenetically close species. A few Bartonella colonies could be observed in the blood of some BALB/c mice by 7 days after inoculation, but no evidence of the persistence of the infection was found. Host specificity suggests the possibility of a long co-speciation of Bartonella species with their rodent hosts. Host–parasite relationships measured by the duration and level of bacteremia and the minimal infectious dose may serve as additional criteria for classification of Bartonella isolates obtained from natural environments.     

PCR-based diagnosis for detection of Leishmania in skin and blood of rodents from an endemic area of cutaneous and visceral leishmaniasis in Brazil

The technique of polymerase chain reaction (PCR) associated to hybridization was used to screen 123 samples collected from wild and synanthropic rodents captured in a cutaneous and visceral leishmaniasis endemic area in the State of Minas Gerais, Brazil. The detection of Leishmania spp in naturally infected rodents is of fundamental importance for incriminating them as possible reservoir hosts of the diseases in Minas Gerais. A total of 62 specimens belonging to wild (Thrichomys apereoides, Oryzomys subflavus, Galea spixii, Bolomys lasiurus and Wiedomys pyrrhorhinos) and synanthropic (R. rattus) rodent species were captured in different ecotopes. Blood and skin samples were submitted for PCR analyses followed by molecular hybridization with specific probes for the three Leishmania-species complexes. Fifteen samples were found positive after PCR-hybridization and identified as follows: nine belonging to the L. mexicana complex, three to the L. braziliensis complex and three to the L. donovani complex. Positive PCR results were found in 11 out of the 61 (18%) blood samples and in four out of the 62 (6.4%) skin fragments screened. R. rattus and T. apereoides were the most abundant species in the area also presenting high prevalence of natural infection. The presence of parasite DNA belonging to L. braziliensis, L. mexicana and L. donovani complexes was confirmed in several individuals of a rodent species, R. rattus. This work is the first report of the detection of L. (L.) chagasi in a naturally infected T. apereoides. The utility of filter paper as a substrate for PCR analyses and the efficacy of the procedure associated to the hybridization is emphasized.     

甘肃草原鼠害区划研究

甘肃草原啮齿类动物区系由68种组成,占全省啮齿动物总种数的75.6%,其中,大多数种的种群密度不超过经济损害水平,有一定的生态学价值;有18～26种的种群密度几乎经常维持在经济损害水平以上,是不同草原类型的优势种害鼠。草原鼠害区划工作应遵循历史发展、生态适应和生产实践的原则。以草原啮齿动物区系组成、地带性生物气候和地带性植被为指标将甘肃草原鼠害划分为5个区;以具有一定优势的地带性草原类型,具有代表性鼠类分布型和优势种害鼠为指标,将甘肃草原鼠害划分为13个草原鼠害亚区。     

Transmission ecology of rodent‐borne diseases: New frontiers

Rodents are recognized reservoir hosts for many human zoonotic pathogens. The current trends resulting from anthropocene defaunation suggest that in the future they, along with other small mammals, are likely to become the dominant mammals in almost all human‐modified environments. Recent intricate studies on bat‐borne emerging diseases have highlighted that many gaps exist in our understanding of the zoonotic transmission of rodent‐borne pathogens. This has emphasized the need for scientists interested in rodent‐borne diseases to integrate rodent ecology into their analysis of rodent‐borne pathogen transmission in order to identify in more detail the mechanisms of spillover and chains of transmission. Further studies are required to better understand the true impact of rodent abundance and the importance of pathogen sharing and circulation in multi‐host– multi‐pathogen communities. We also need to explore in more depth the roles of generalist and abundant species as the potential links between pathogen‐sharing, co‐infections and disease transmission.     

基于PDA的草原鼠害数据采集系统的开发

为提高草原鼠害监测的规范性、数据采集效率和数据传输的实时性,本文分析了当前数据采集的特点,以C#为开发工具,将PDA、GPS、XML等技术综合集成进行基于PDA的草原鼠害数据采集系统的研发,开发出空间采集法、定点采集法、定面积捕尽法和铗日采集法等应用工具软件,实现了草原害鼠数据采集的半自动化,改变了传统野外数据采集方式,提高了工作效率。     

中新天津生态城夏季啮齿类的空间生态位

2008年夏季对中新天津生态城的啮齿动物进行调查,采用Shannon-Wiener生态位宽度指数和Pianka生态位重叠指数对啮齿动物空间生态位进行了研究。结果表明,在捕获的5种啮齿动物中,小家鼠和黑线姬鼠的空间生态位宽度指数最高,分别为0.97和0.78;褐家鼠(Bi=0.58)和黑线仓鼠(Bi=0.51)次之;大仓鼠(Bi=0.36)最低。除了黑线姬鼠与其他4种啮齿动物两两之间空间生态位重叠指数均较小(C_P<0.50)外,其他4种啮齿动物两两之间均较高(C_P>0.50)。黑线仓鼠与褐家鼠空间生态位几乎完全重叠(C_P=0.99),在10对啮齿动物中,共有7对之间的空间生态位重叠指数大于0.70。由此可见,生态城啮齿动物之间存在资源竞争,主要原因是生态城是典型的盐碱湿地,可利用资源不丰富,使得动物分布相对集中,增加种间竞争。     

Modelling relative abundance of Oligoryzomys flavescens,an Orthohantavirus reservoir,in an endemic hantavirus pulmonary syndrome zone

Hantavirus pulmonary syndrome (HPS) is a zoonotic emerging infectious disease caused by New World orthohantaviruses (family Hantaviridae) hosted by rodents of the family Cricetidae. In Argentina, one of its main hosts is the sigmodontine rodent Oligoryzomys flavescens, a widely distributed mouse of the Pampas, Delta and Espinal ecoregions of central-east Argentina. Because the abundance of the reservoir and its proportion in the rodent community affects both virus prevalence and human exposure risk, its estimation throughout its known geographical distribution is of key importance for the design of public health strategies to prevent HPS. The aim of this study was therefore to model the relative abundance of O. flavescens in most of the Pampas ecoregion within Buenos Aires Province, Argentina, where hantavirus pulmonary syndrome is endemic. To do this we used owl-pellet samples collected between 2006 and 2008 from 51 sites distributed throughout most of Buenos Aires province. Mammalian prey in each pellet was identified to the lowest possible taxonomic level by examination of the skulls, dentaries and molars. We modelled the frequency of O. flavescens found in each sample as a function of climatic, environmental, and topographic data of each site. The two best models were applied to a Geo referential Information System to build maps of estimated frequency (as a proxy of relative abundance) within Buenos Aires province. Estimated relative abundance of O. flavescens in Buenos Aires province was significantly associated with annual mean temperature, annual precipitation and presence of freshwater bodies, and varied among sub-regions, with the Inland and Rolling Pampas being the regions with highest frequencies. Knowing in which areas O. flavescens abundance is expected to be higher can be used to concentrate limited sanitary efforts in those areas that are most needed in order to reduce transmission and increase detection.     

Suitability of day‐old chicks as food for captive snakes

Snakes are increasingly kept by private hobbyists and their numbers in the pet trade are increasing. Since suitable diets are essential for the health, welfare and maintenance of captive animals, objective research is required to improve and evaluate current feeding practices. Unfortunately, the husbandry of reptiles is frequently led by tradition, resulting in methods which are not evidence based. One such occurrence is the widespread belief that day‐old chicks (DOCs) are unsuitable as food for captive snakes. Since this assumption has not been systematically assessed, herein I review the evidence in order to provide a more informed basis from which to evaluate the suitability of chicks in relation to rodent prey. Commonly expressed nutritional, ecological and husbandry‐related concerns are examined using compilations of previously published data, new data, prior experience and nutrient compositions obtained from the Zootrition? database. Day‐old chicks were compared with two rodent species (mice and rats) since these are the most commonly used alternative prey item. Rodents were clearly the better option only in their ‘naturalness’, in that mammalian prey species are more frequently represented in natural diets than birds. I conclude that DOCs are a suitable prey item for snakes in captive collections since the available data provide no firm evidence for their avoidance, contrary to popular belief. Many gaps in our knowledge remain that would assist further discussion of this issue, and these are highlighted within. It is pertinent that although these data indicate that DOCs are a viable alternative to rodent prey for captive snakes, they do not necessarily indicate its superiority. In most instances, rodents and DOCs may be regarded as practically equivalent and interchangeable. It is therefore the individual keeper’s preference as to which to use, informed in particular circumstances by the information presented herein.